# EnsembleVoteClassifier

Implementation of a majority voting EnsembleVoteClassifier for classification.

from mlxtend.classifier import EnsembleVoteClassifier

# Overview

The EnsembleVoteClassifier is a meta-classifier for combining similar or conceptually different machine learning classifiers for classification via majority or plurality voting. (For simplicity, we will refer to both majority and plurality voting as majority voting.)

The EnsembleVoteClassifier implements "hard" and "soft" voting. In hard voting, we predict the final class label as the class label that has been predicted most frequently by the classification models. In soft voting, we predict the class labels by averaging the class-probabilities (only recommended if the classifiers are well-calibrated).

Note

If you are interested in using the EnsembleVoteClassifier, please note that it is now also available through scikit learn (>0.17) as VotingClassifier.

### Majority Voting / Hard Voting

Hard voting is the simplest case of majority voting. Here, we predict the class label $\hat{y}$ via majority (plurality) voting of each classifier $C_j$:

Assuming that we combine three classifiers that classify a training sample as follows:

• classifier 1 -> class 0
• classifier 2 -> class 0
• classifier 3 -> class 1

Via majority vote, we would we would classify the sample as "class 0."

### Weighted Majority Vote

In addition to the simple majority vote (hard voting) as described in the previous section, we can compute a weighted majority vote by associating a weight $w_j$ with classifier $C_j$:

where $\chi_A$ is the characteristic function $[C_j(\mathbf{x}) = i \; \in A]$, and $A$ is the set of unique class labels.

Continuing with the example from the previous section

• classifier 1 -> class 0
• classifier 2 -> class 0
• classifier 3 -> class 1

assigning the weights {0.2, 0.2, 0.6} would yield a prediction $\hat{y} = 1$:

### Soft Voting

In soft voting, we predict the class labels based on the predicted probabilities $p$ for classifier -- this approach is only recommended if the classifiers are well-calibrated.

where $w_j$ is the weight that can be assigned to the $j$th classifier.

Assuming the example in the previous section was a binary classification task with class labels $i \in \{0, 1\}$, our ensemble could make the following prediction:

• $C_1(\mathbf{x}) \rightarrow [0.9, 0.1]$
• $C_2(\mathbf{x}) \rightarrow [0.8, 0.2]$
• $C_3(\mathbf{x}) \rightarrow [0.4, 0.6]$

Using uniform weights, we compute the average probabilities:

However, assigning the weights {0.1, 0.1, 0.8} would yield a prediction $\hat{y} = 1$:

## Example 1 - Classifying Iris Flowers Using Different Classification Models

from sklearn import datasets

X, y = iris.data[:, 1:3], iris.target

from sklearn import model_selection
from sklearn.linear_model import LogisticRegression
from sklearn.naive_bayes import GaussianNB
from sklearn.ensemble import RandomForestClassifier
import numpy as np

clf1 = LogisticRegression(random_state=1)
clf2 = RandomForestClassifier(random_state=1)
clf3 = GaussianNB()

print('5-fold cross validation:\n')

labels = ['Logistic Regression', 'Random Forest', 'Naive Bayes']

for clf, label in zip([clf1, clf2, clf3], labels):

scores = model_selection.cross_val_score(clf, X, y,
cv=5,
scoring='accuracy')
print("Accuracy: %0.2f (+/- %0.2f) [%s]"
% (scores.mean(), scores.std(), label))

5-fold cross validation:

Accuracy: 0.95 (+/- 0.04) [Logistic Regression]
Accuracy: 0.94 (+/- 0.04) [Random Forest]
Accuracy: 0.91 (+/- 0.04) [Naive Bayes]

from mlxtend.classifier import EnsembleVoteClassifier

eclf = EnsembleVoteClassifier(clfs=[clf1, clf2, clf3], weights=[1,1,1])

labels = ['Logistic Regression', 'Random Forest', 'Naive Bayes', 'Ensemble']
for clf, label in zip([clf1, clf2, clf3, eclf], labels):

scores = model_selection.cross_val_score(clf, X, y,
cv=5,
scoring='accuracy')
print("Accuracy: %0.2f (+/- %0.2f) [%s]"
% (scores.mean(), scores.std(), label))

Accuracy: 0.95 (+/- 0.04) [Logistic Regression]
Accuracy: 0.94 (+/- 0.04) [Random Forest]
Accuracy: 0.91 (+/- 0.04) [Naive Bayes]
Accuracy: 0.95 (+/- 0.04) [Ensemble]


#### Plotting Decision Regions

import matplotlib.pyplot as plt
from mlxtend.plotting import plot_decision_regions
import matplotlib.gridspec as gridspec
import itertools

gs = gridspec.GridSpec(2, 2)

fig = plt.figure(figsize=(10,8))

labels = ['Logistic Regression', 'Random Forest', 'Naive Bayes', 'Ensemble']
for clf, lab, grd in zip([clf1, clf2, clf3, eclf],
labels,
itertools.product([0, 1], repeat=2)):

clf.fit(X, y)
ax = plt.subplot(gs[grd[0], grd[1]])
fig = plot_decision_regions(X=X, y=y, clf=clf)
plt.title(lab)

/Users/kani/Documents/KatrinaLand/mlxtend/mlxtend/plotting/decision_regions.py:249: MatplotlibDeprecationWarning: Passing unsupported keyword arguments to axis() will raise a TypeError in 3.3.
ax.axis(xmin=xx.min(), xmax=xx.max(), y_min=yy.min(), y_max=yy.max())
/Users/kani/Documents/KatrinaLand/mlxtend/mlxtend/plotting/decision_regions.py:249: MatplotlibDeprecationWarning: Passing unsupported keyword arguments to axis() will raise a TypeError in 3.3.
ax.axis(xmin=xx.min(), xmax=xx.max(), y_min=yy.min(), y_max=yy.max())
/Users/kani/Documents/KatrinaLand/mlxtend/mlxtend/plotting/decision_regions.py:249: MatplotlibDeprecationWarning: Passing unsupported keyword arguments to axis() will raise a TypeError in 3.3.
ax.axis(xmin=xx.min(), xmax=xx.max(), y_min=yy.min(), y_max=yy.max())
/Users/kani/Documents/KatrinaLand/mlxtend/mlxtend/plotting/decision_regions.py:249: MatplotlibDeprecationWarning: Passing unsupported keyword arguments to axis() will raise a TypeError in 3.3.
ax.axis(xmin=xx.min(), xmax=xx.max(), y_min=yy.min(), y_max=yy.max())


from sklearn import datasets

X, y = iris.data[:, 1:3], iris.target

from sklearn.model_selection import GridSearchCV
from sklearn.linear_model import LogisticRegression
from sklearn.naive_bayes import GaussianNB
from sklearn.ensemble import RandomForestClassifier
from mlxtend.classifier import EnsembleVoteClassifier

clf1 = LogisticRegression(random_state=1)
clf2 = RandomForestClassifier(random_state=1)
clf3 = GaussianNB()
eclf = EnsembleVoteClassifier(clfs=[clf1, clf2, clf3], voting='soft')

params = {'logisticregression__C': [1.0, 100.0],
'randomforestclassifier__n_estimators': [20, 200],}

grid = GridSearchCV(estimator=eclf, param_grid=params, cv=5)
grid.fit(iris.data, iris.target)

cv_keys = ('mean_test_score', 'std_test_score', 'params')

for r, _ in enumerate(grid.cv_results_['mean_test_score']):
print("%0.3f +/- %0.2f %r"
% (grid.cv_results_[cv_keys[0]][r],
grid.cv_results_[cv_keys[1]][r] / 2.0,
grid.cv_results_[cv_keys[2]][r]))

/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)

0.953 +/- 0.01 {'logisticregression__C': 1.0, 'randomforestclassifier__n_estimators': 20}
0.960 +/- 0.01 {'logisticregression__C': 1.0, 'randomforestclassifier__n_estimators': 200}
0.960 +/- 0.01 {'logisticregression__C': 100.0, 'randomforestclassifier__n_estimators': 20}
0.960 +/- 0.01 {'logisticregression__C': 100.0, 'randomforestclassifier__n_estimators': 200}


Note: If the EnsembleClassifier is initialized with multiple similar estimator objects, the estimator names are modified with consecutive integer indices, for example:

clf1 = LogisticRegression(random_state=1)
clf2 = RandomForestClassifier(random_state=1)
eclf = EnsembleVoteClassifier(clfs=[clf1, clf1, clf2],
voting='soft')

params = {'logisticregression-1__C': [1.0, 100.0],
'logisticregression-2__C': [1.0, 100.0],
'randomforestclassifier__n_estimators': [20, 200],}

grid = GridSearchCV(estimator=eclf, param_grid=params, cv=5)
grid = grid.fit(iris.data, iris.target)

/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)


Note

The EnsembleVoteClass also enables grid search over the clfs argument. However, due to the current implementation of GridSearchCV in scikit-learn, it is not possible to search over both, differenct classifiers and classifier parameters at the same time. For instance, while the following parameter dictionary works

params = {'randomforestclassifier__n_estimators': [1, 100],
'clfs': [(clf1, clf1, clf1), (clf2, clf3)]}


it will use the instance settings of clf1, clf2, and clf3 and not overwrite it with the 'n_estimators' settings from 'randomforestclassifier__n_estimators': [1, 100].

## Example 3 - Majority voting with classifiers trained on different feature subsets

Feature selection algorithms implemented in scikit-learn as well as the SequentialFeatureSelector implement a transform method that passes the reduced feature subset to the next item in a Pipeline.

For example, the method

def transform(self, X):
return X[:, self.k_feature_idx_]


returns the best feature columns, k_feature_idx_, given a dataset X.

Thus, we simply need to construct a Pipeline consisting of the feature selector and the classifier in order to select different feature subsets for different algorithms. During fitting, the optimal feature subsets are automatically determined via the GridSearchCV object, and by calling predict, the fitted feature selector in the pipeline only passes these columns along, which resulted in the best performance for the respective classifier.

from sklearn import datasets

X, y = iris.data[:, :], iris.target

from sklearn.model_selection import GridSearchCV
from sklearn.linear_model import LogisticRegression
from sklearn.naive_bayes import GaussianNB
from sklearn.ensemble import RandomForestClassifier
from mlxtend.classifier import EnsembleVoteClassifier
from sklearn.pipeline import Pipeline
from mlxtend.feature_selection import SequentialFeatureSelector

clf1 = LogisticRegression(random_state=1)
clf2 = RandomForestClassifier(random_state=1)
clf3 = GaussianNB()

# Creating a feature-selection-classifier pipeline

sfs1 = SequentialFeatureSelector(clf1,
k_features=4,
forward=True,
floating=False,
scoring='accuracy',
verbose=0,
cv=0)

clf1_pipe = Pipeline([('sfs', sfs1),
('logreg', clf1)])

eclf = EnsembleVoteClassifier(clfs=[clf1_pipe, clf2, clf3],
voting='soft')

params = {'pipeline__sfs__k_features': [1, 2, 3],
'pipeline__logreg__C': [1.0, 100.0],
'randomforestclassifier__n_estimators': [20, 200]}

grid = GridSearchCV(estimator=eclf, param_grid=params, cv=5)
grid.fit(iris.data, iris.target)

cv_keys = ('mean_test_score', 'std_test_score', 'params')

for r, _ in enumerate(grid.cv_results_['mean_test_score']):
print("%0.3f +/- %0.2f %r"
% (grid.cv_results_[cv_keys[0]][r],
grid.cv_results_[cv_keys[1]][r] / 2.0,
grid.cv_results_[cv_keys[2]][r]))

/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)
/Users/kani/Documents/KatrinaLand/mlxtend/venv/lib/python3.7/site-packages/sklearn/linear_model/_logistic.py:940: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)

0.947 +/- 0.02 {'pipeline__logreg__C': 1.0, 'pipeline__sfs__k_features': 1, 'randomforestclassifier__n_estimators': 20}
0.947 +/- 0.02 {'pipeline__logreg__C': 1.0, 'pipeline__sfs__k_features': 1, 'randomforestclassifier__n_estimators': 200}
0.947 +/- 0.02 {'pipeline__logreg__C': 1.0, 'pipeline__sfs__k_features': 2, 'randomforestclassifier__n_estimators': 20}
0.960 +/- 0.01 {'pipeline__logreg__C': 1.0, 'pipeline__sfs__k_features': 2, 'randomforestclassifier__n_estimators': 200}
0.953 +/- 0.01 {'pipeline__logreg__C': 1.0, 'pipeline__sfs__k_features': 3, 'randomforestclassifier__n_estimators': 20}
0.960 +/- 0.01 {'pipeline__logreg__C': 1.0, 'pipeline__sfs__k_features': 3, 'randomforestclassifier__n_estimators': 200}
0.953 +/- 0.01 {'pipeline__logreg__C': 100.0, 'pipeline__sfs__k_features': 1, 'randomforestclassifier__n_estimators': 20}
0.953 +/- 0.01 {'pipeline__logreg__C': 100.0, 'pipeline__sfs__k_features': 1, 'randomforestclassifier__n_estimators': 200}
0.960 +/- 0.01 {'pipeline__logreg__C': 100.0, 'pipeline__sfs__k_features': 2, 'randomforestclassifier__n_estimators': 20}
0.960 +/- 0.01 {'pipeline__logreg__C': 100.0, 'pipeline__sfs__k_features': 2, 'randomforestclassifier__n_estimators': 200}
0.960 +/- 0.01 {'pipeline__logreg__C': 100.0, 'pipeline__sfs__k_features': 3, 'randomforestclassifier__n_estimators': 20}
0.960 +/- 0.01 {'pipeline__logreg__C': 100.0, 'pipeline__sfs__k_features': 3, 'randomforestclassifier__n_estimators': 200}


The best parameters determined via GridSearch are:

grid.best_params_

{'pipeline__logreg__C': 1.0,
'pipeline__sfs__k_features': 2,
'randomforestclassifier__n_estimators': 200}


Now, we assign these parameters to the ensemble voting classifier, fit the models on the complete training set, and perform a prediction on 3 samples from the Iris dataset.

eclf = eclf.set_params(**grid.best_params_)
eclf.fit(X, y).predict(X[[1, 51, 149]])

array([0, 1, 2])


#### Manual Approach

Alternatively, we can select different columns "manually" using the ColumnSelector object. In this example, we select only the first (sepal length) and third (petal length) column for the logistic regression classifier (clf1).

from mlxtend.feature_selection import ColumnSelector

col_sel = ColumnSelector(cols=[0, 2])

clf1_pipe = Pipeline([('sel', col_sel),
('logreg', clf1)])

eclf = EnsembleVoteClassifier(clfs=[clf1_pipe, clf2, clf3],
voting='soft')
eclf.fit(X, y).predict(X[[1, 51, 149]])

array([0, 1, 2])


Furthermore, we can fit the SequentialFeatureSelector separately, outside the grid search hyperparameter optimization pipeline. Here, we determine the best features first, and then we construct a pipeline using these "fixed," best features as seed for the ColumnSelector:

sfs1 = SequentialFeatureSelector(clf1,
k_features=2,
forward=True,
floating=False,
scoring='accuracy',
verbose=1,
cv=0)

sfs1.fit(X, y)

print('Best features', sfs1.k_feature_idx_)

col_sel = ColumnSelector(cols=sfs1.k_feature_idx_)

clf1_pipe = Pipeline([('sel', col_sel),
('logreg', clf1)])

[Parallel(n_jobs=1)]: Using backend SequentialBackend with 1 concurrent workers.
[Parallel(n_jobs=1)]: Done   4 out of   4 | elapsed:    0.0s finished
Features: 1/2[Parallel(n_jobs=1)]: Using backend SequentialBackend with 1 concurrent workers.
[Parallel(n_jobs=1)]: Done   3 out of   3 | elapsed:    0.0s finished
Features: 2/2

Best features (2, 3)

eclf = EnsembleVoteClassifier(clfs=[clf1_pipe, clf2, clf3],
voting='soft')
eclf.fit(X, y).predict(X[[1, 51, 149]])

array([0, 1, 2])


## Example 5 - Using Pre-fitted Classifiers

from sklearn import datasets

X, y = iris.data[:, 1:3], iris.target


Assume that we previously fitted our classifiers:

from sklearn import model_selection
from sklearn.linear_model import LogisticRegression
from sklearn.naive_bayes import GaussianNB
from sklearn.ensemble import RandomForestClassifier
import numpy as np

clf1 = LogisticRegression(random_state=1)
clf2 = RandomForestClassifier(random_state=1)
clf3 = GaussianNB()

for clf in (clf1, clf2, clf3):
clf.fit(X, y)


By setting fit_base_estimators=False, it will enforce use_clones to be False and the EnsembleVoteClassifier will not re-fit these classifers to save computational time:

from mlxtend.classifier import EnsembleVoteClassifier
import copy
eclf = EnsembleVoteClassifier(clfs=[clf1, clf2, clf3], weights=[1,1,1], fit_base_estimators=False)

labels = ['Logistic Regression', 'Random Forest', 'Naive Bayes', 'Ensemble']

eclf.fit(X, y)

print('accuracy:', np.mean(y == eclf.predict(X)))

Warning: enforce use_clones to be False
accuracy: 0.96


However, please note that fit_base_estimators=False is incompatible to any form of cross-validation that is done in e.g., model_selection.cross_val_score or model_selection.GridSearchCV, etc., since it would require the classifiers to be refit to the training folds. Thus, only use fit_base_estimators=False if you want to make a prediction directly without cross-validation.

## Example 6 - Ensembles of Classifiers that Operate on Different Feature Subsets

If desired, the different classifiers can be fit to different subsets of features in the training dataset. The following example illustrates how this can be done on a technical level using scikit-learn pipelines and the ColumnSelector:

from sklearn.datasets import load_iris
from mlxtend.classifier import EnsembleVoteClassifier
from mlxtend.feature_selection import ColumnSelector
from sklearn.pipeline import make_pipeline
from sklearn.linear_model import LogisticRegression

X = iris.data
y = iris.target

pipe1 = make_pipeline(ColumnSelector(cols=(0, 2)),
LogisticRegression())
pipe2 = make_pipeline(ColumnSelector(cols=(1, 2, 3)),
LogisticRegression())

eclf = EnsembleVoteClassifier(clfs=[pipe1, pipe2])

eclf.fit(X, y)

EnsembleVoteClassifier(clfs=[Pipeline(memory=None,
steps=[('columnselector',
ColumnSelector(cols=(0, 2),
drop_axis=False)),
('logisticregression',
LogisticRegression(C=1.0,
class_weight=None,
dual=False,
fit_intercept=True,
intercept_scaling=1,
l1_ratio=None,
max_iter=100,
multi_class='auto',
n_jobs=None,
penalty='l2',
random_state=None,
solver='lbfgs',
tol=0.0001,
v...
('logisticregression',
LogisticRegression(C=1.0,
class_weight=None,
dual=False,
fit_intercept=True,
intercept_scaling=1,
l1_ratio=None,
max_iter=100,
multi_class='auto',
n_jobs=None,
penalty='l2',
random_state=None,
solver='lbfgs',
tol=0.0001,
verbose=0,
warm_start=False))],
verbose=False)],
fit_base_estimators=True, use_clones=True, verbose=0,
voting='hard', weights=None)


## Example 7 - A Note about Scikit-Learn SVMs and Soft Voting

This section provides some additional technical insights in how probabilities are used when voting='soft'.

Note that scikit-learn estimates the probabilities for SVMs (more info here: http://scikit-learn.org/stable/modules/svm.html#scores-probabilities) in a way that these may not be consistent with the class labels that the SVM predicts. This is an extreme example, but let's say we have a dataset with 3 class labels, 0, 1, and 2. For a given training example, the SVM classifier may predict class 2. However, the class-membership probabilities may look as follows:

• class 0: 99%
• class 1: 0.5%
• class 2: 0.5%

A practical example of this scenario is shown below:

import numpy as np
from mlxtend.classifier import EnsembleVoteClassifier
from sklearn.svm import SVC

X, y = iris.data, iris.target

clf2 = SVC(probability=True, random_state=4)
clf2.fit(X, y)
eclf = EnsembleVoteClassifier(clfs=[clf2], voting='soft', fit_base_estimators=False)
eclf.fit(X, y)

for svm_class, e_class, svm_prob, e_prob, in zip(clf2.predict(X),
eclf.predict(X),
clf2.predict_proba(X),
eclf.predict_proba(X)):
if svm_class != e_class:
print('============')
print('Probas from SVM            :', svm_prob)
print('Class from SVM             :', svm_class)
print('Probas from SVM in Ensemble:', e_prob)
print('Class from SVM in Ensemble :', e_class)
print('============')

Warning: enforce use_clones to be False
============
Probas from SVM            : [0.00910384 0.47821605 0.51268012]
Class from SVM             : 1
Probas from SVM in Ensemble: [0.00910384 0.47821605 0.51268012]
Class from SVM in Ensemble : 2
============


Based on the probabilities, we would expect the SVM to predict class 2, because it has the highest probability. Since the EnsembleVoteClassifier uses the argmax function internally if voting='soft', it would indeed predict class 2 in this case even if the ensemble consists of only one SVM model.

Note that in practice, this minor technical detail does not need to concern you, but it is useful to keep it in mind in case you are wondering about results from a 1-model SVM ensemble compared to that SVM alone -- this is not a bug.