Plotting Decision Regions

A function for plotting decision regions of classifiers in 1 or 2 dimensions.

from mlxtend.plotting import plot_decision_regions

References

Example 1 - Decision regions in 2D

from mlxtend.plotting import plot_decision_regions
import matplotlib.pyplot as plt
from sklearn import datasets
from sklearn.svm import SVC

# Loading some example data
iris = datasets.load_iris()
X = iris.data[:, [0, 2]]
y = iris.target

# Training a classifier
svm = SVC(C=0.5, kernel='linear')
svm.fit(X, y)


# Plotting decision regions
plot_decision_regions(X, y, clf=svm, legend=2)

# Adding axes annotations
plt.xlabel('sepal length [cm]')
plt.ylabel('petal length [cm]')
plt.title('SVM on Iris')
plt.show()

png

Example 2 - Decision regions in 1D

from mlxtend.plotting import plot_decision_regions
import matplotlib.pyplot as plt
from sklearn import datasets
from sklearn.svm import SVC

# Loading some example data
iris = datasets.load_iris()
X = iris.data[:, 2]
X = X[:, None]
y = iris.target

# Training a classifier
svm = SVC(C=0.5, kernel='linear')
svm.fit(X, y)

# Plotting decision regions
plot_decision_regions(X, y, clf=svm, legend=2)

# Adding axes annotations
plt.xlabel('sepal length [cm]')
plt.title('SVM on Iris')

plt.show()

png

Example 3 - Decision Region Grids

from sklearn.linear_model import LogisticRegression
from sklearn.naive_bayes import GaussianNB 
from sklearn.ensemble import RandomForestClassifier
from sklearn.svm import SVC
from sklearn import datasets
import numpy as np

# Initializing Classifiers
clf1 = LogisticRegression(random_state=1,
                          solver='newton-cg',
                          multi_class='multinomial')
clf2 = RandomForestClassifier(random_state=1, n_estimators=100)
clf3 = GaussianNB()
clf4 = SVC(gamma='auto')

# Loading some example data
iris = datasets.load_iris()
X = iris.data[:, [0,2]]
y = iris.target

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', 'SVM']
for clf, lab, grd in zip([clf1, clf2, clf3, clf4],
                         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, legend=2)
    plt.title(lab)

plt.show()

png

Example 4 - Highlighting Test Data Points

from mlxtend.plotting import plot_decision_regions
from mlxtend.preprocessing import shuffle_arrays_unison
import matplotlib.pyplot as plt
from sklearn import datasets
from sklearn.svm import SVC


# Loading some example data
iris = datasets.load_iris()
X, y = iris.data[:, [0,2]], iris.target
X, y = shuffle_arrays_unison(arrays=[X, y], random_seed=3)

X_train, y_train = X[:100], y[:100]
X_test, y_test = X[100:], y[100:]

# Training a classifier
svm = SVC(C=0.5, kernel='linear')
svm.fit(X_train, y_train)

# Plotting decision regions
plot_decision_regions(X, y, clf=svm, legend=2, 
                      X_highlight=X_test)

# Adding axes annotations
plt.xlabel('sepal length [cm]')
plt.ylabel('petal length [cm]')
plt.title('SVM on Iris')
plt.show()

png

Example 5 - Evaluating Classifier Behavior on Non-Linear Problems

from sklearn.linear_model import LogisticRegression
from sklearn.naive_bayes import GaussianNB 
from sklearn.ensemble import RandomForestClassifier
from sklearn.svm import SVC

# Initializing Classifiers
clf1 = LogisticRegression(random_state=1, solver='lbfgs')
clf2 = RandomForestClassifier(n_estimators=100, 
                              random_state=1)
clf3 = GaussianNB()
clf4 = SVC(gamma='auto')

# Loading Plotting Utilities
import matplotlib.pyplot as plt
import matplotlib.gridspec as gridspec
import itertools
from mlxtend.plotting import plot_decision_regions
import numpy as np

XOR

xx, yy = np.meshgrid(np.linspace(-3, 3, 50),
                     np.linspace(-3, 3, 50))
rng = np.random.RandomState(0)
X = rng.randn(300, 2)
y = np.array(np.logical_xor(X[:, 0] > 0, X[:, 1] > 0), 
             dtype=int)

gs = gridspec.GridSpec(2, 2)

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

labels = ['Logistic Regression', 'Random Forest', 'Naive Bayes', 'SVM']
for clf, lab, grd in zip([clf1, clf2, clf3, clf4],
                         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, legend=2)
    plt.title(lab)

plt.show()

png

Half-Moons

from sklearn.datasets import make_moons
X, y = make_moons(n_samples=100, random_state=123)

gs = gridspec.GridSpec(2, 2)

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

labels = ['Logistic Regression', 'Random Forest', 'Naive Bayes', 'SVM']
for clf, lab, grd in zip([clf1, clf2, clf3, clf4],
                         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, legend=2)
    plt.title(lab)

plt.show()

png

Concentric Circles

from sklearn.datasets import make_circles
X, y = make_circles(n_samples=1000, random_state=123, noise=0.1, factor=0.2)

gs = gridspec.GridSpec(2, 2)

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

labels = ['Logistic Regression', 'Random Forest', 'Naive Bayes', 'SVM']
for clf, lab, grd in zip([clf1, clf2, clf3, clf4],
                         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, legend=2)
    plt.title(lab)

plt.show()

png

Example 6 - Working with existing axes objects using subplots

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

from sklearn.linear_model import LogisticRegression
from sklearn.naive_bayes import GaussianNB 
from sklearn import datasets
import numpy as np

# Loading some example data
iris = datasets.load_iris()
X = iris.data[:, 2]
X = X[:, None]
y = iris.target

# Initializing and fitting classifiers
clf1 = LogisticRegression(random_state=1,
                          solver='lbfgs',
                          multi_class='multinomial')
clf2 = GaussianNB()
clf1.fit(X, y)
clf2.fit(X, y)

fig, axes = plt.subplots(1, 2, figsize=(10, 3))

fig = plot_decision_regions(X=X, y=y, clf=clf1, ax=axes[0], legend=2)
fig = plot_decision_regions(X=X, y=y, clf=clf2, ax=axes[1], legend=1)

plt.show()

png

Example 7 - Decision regions with more than two training features

from mlxtend.plotting import plot_decision_regions
import matplotlib.pyplot as plt
from sklearn import datasets
from sklearn.svm import SVC

# Loading some example data
X, y = datasets.make_blobs(n_samples=600, n_features=3,
                           centers=[[2, 2, -2],[-2, -2, 2]],
                           cluster_std=[2, 2], random_state=2)

# Training a classifier
svm = SVC(gamma='auto')
svm.fit(X, y)

# Plotting decision regions
fig, ax = plt.subplots()
# Decision region for feature 3 = 1.5
value = 1.5
# Plot training sample with feature 3 = 1.5 +/- 0.75
width = 0.75
plot_decision_regions(X, y, clf=svm,
                      filler_feature_values={2: value},
                      filler_feature_ranges={2: width},
                      legend=2, ax=ax)
ax.set_xlabel('Feature 1')
ax.set_ylabel('Feature 2')
ax.set_title('Feature 3 = {}'.format(value))

# Adding axes annotations
fig.suptitle('SVM on make_blobs')
plt.show()

png

Example 8 - Grid of decision region slices

from mlxtend.plotting import plot_decision_regions
import matplotlib.pyplot as plt
from sklearn import datasets
from sklearn.svm import SVC

# Loading some example data
X, y = datasets.make_blobs(n_samples=500, n_features=3, centers=[[2, 2, -2],[-2, -2, 2]],
                           cluster_std=[2, 2], random_state=2)

# Training a classifier
svm = SVC(gamma='auto')
svm.fit(X, y)

# Plotting decision regions
fig, axarr = plt.subplots(2, 2, figsize=(10,8), sharex=True, sharey=True)
values = [-4.0, -1.0, 1.0, 4.0]
width = 0.75
for value, ax in zip(values, axarr.flat):
    plot_decision_regions(X, y, clf=svm,
                          filler_feature_values={2: value},
                          filler_feature_ranges={2: width},
                          legend=2, ax=ax)
    ax.set_xlabel('Feature 1')
    ax.set_ylabel('Feature 2')
    ax.set_title('Feature 3 = {}'.format(value))

# Adding axes annotations
fig.suptitle('SVM on make_blobs')
plt.show()

png

Example 9 - Customizing the plotting style

from mlxtend.plotting import plot_decision_regions
from mlxtend.preprocessing import shuffle_arrays_unison
import matplotlib.pyplot as plt
from sklearn import datasets
from sklearn.svm import SVC

# Loading some example data
iris = datasets.load_iris()
X = iris.data[:, [0, 2]]
y = iris.target
X, y = shuffle_arrays_unison(arrays=[X, y], random_seed=3)
X_train, y_train = X[:100], y[:100]
X_test, y_test = X[100:], y[100:]

# Training a classifier
svm = SVC(C=0.5, kernel='linear')
svm.fit(X_train, y_train)

# Specify keyword arguments to be passed to underlying plotting functions
scatter_kwargs = {'s': 120, 'edgecolor': None, 'alpha': 0.7}
contourf_kwargs = {'alpha': 0.2}
scatter_highlight_kwargs = {'s': 120, 'label': 'Test data', 'alpha': 0.7}
# Plotting decision regions
plot_decision_regions(X, y, clf=svm, legend=2,
                      X_highlight=X_test,
                      scatter_kwargs=scatter_kwargs,
                      contourf_kwargs=contourf_kwargs,
                      scatter_highlight_kwargs=scatter_highlight_kwargs)

# Adding axes annotations
plt.xlabel('sepal length [cm]')
plt.ylabel('petal length [cm]')
plt.title('SVM on Iris')
plt.show()

png

Example 10 - Providing your own legend labels

Custom legend labels can be provided by returning the axis object(s) from the plot_decision_region function and then getting the handles and labels of the legend. Custom handles (i.e., labels) can then be provided via ax.legend

ax = plot_decision_regions(X, y, clf=svm, legend=0)

handles, labels = ax.get_legend_handles_labels()
ax.legend(handles, 
          ['class 0', 'class 1', 'class 2'], 
           framealpha=0.3, scatterpoints=1)

An example is shown below.

from mlxtend.plotting import plot_decision_regions
import matplotlib.pyplot as plt
from sklearn import datasets
from sklearn.svm import SVC

# Loading some example data
iris = datasets.load_iris()
X = iris.data[:, [0, 2]]
y = iris.target

# Training a classifier
svm = SVC(C=0.5, kernel='linear')
svm.fit(X, y)


# Plotting decision regions
ax = plot_decision_regions(X, y, clf=svm, legend=0)

# Adding axes annotations
plt.xlabel('sepal length [cm]')
plt.ylabel('petal length [cm]')
plt.title('SVM on Iris')

handles, labels = ax.get_legend_handles_labels()
ax.legend(handles, 
          ['class square', 'class triangle', 'class circle'], 
           framealpha=0.3, scatterpoints=1)

plt.show()

png

API

plot_decision_regions(X, y, clf, feature_index=None, filler_feature_values=None, filler_feature_ranges=None, ax=None, X_highlight=None, res=None, legend=1, hide_spines=True, markers='s^oxv<>', colors='#1f77b4,#ff7f0e,#3ca02c,#d62728,#9467bd,#8c564b,#e377c2,#7f7f7f,#bcbd22,#17becf', scatter_kwargs=None, contourf_kwargs=None, scatter_highlight_kwargs=None)

Plot decision regions of a classifier.

Please note that this functions assumes that class labels are labeled consecutively, e.g,. 0, 1, 2, 3, 4, and 5. If you have class labels with integer labels > 4, you may want to provide additional colors and/or markers as colors and markers arguments. See http://matplotlib.org/examples/color/named_colors.html for more information.

Parameters

X : array-like, shape = [n_samples, n_features]

Feature Matrix.
y : array-like, shape = [n_samples]

True class labels.
clf : Classifier object.

Must have a .predict method.
feature_index : array-like (default: (0,) for 1D, (0, 1) otherwise)

Feature indices to use for plotting. The first index in feature_index will be on the x-axis, the second index will be on the y-axis.
filler_feature_values : dict (default: None)

Only needed for number features > 2. Dictionary of feature index-value pairs for the features not being plotted.
filler_feature_ranges : dict (default: None)

Only needed for number features > 2. Dictionary of feature index-value pairs for the features not being plotted. Will use the ranges provided to select training samples for plotting.
ax : matplotlib.axes.Axes (default: None)

An existing matplotlib Axes. Creates one if ax=None.
X_highlight : array-like, shape = [n_samples, n_features] (default: None)

An array with data points that are used to highlight samples in X.
res : float or array-like, shape = (2,) (default: None)

This parameter was used to define the grid width, but it has been deprecated in favor of determining the number of points given the figure DPI and size automatically for optimal results and computational efficiency. To increase the resolution, it's is recommended to use to provide a dpi argument via matplotlib, e.g.,plt.figure(dpi=600)`.
hide_spines : bool (default: True)

Hide axis spines if True.
legend : int (default: 1)

Integer to specify the legend location. No legend if legend is 0.
markers : str (default: 's^oxv<>')

Scatterplot markers.
colors : str (default: 'red,blue,limegreen,gray,cyan')

Comma separated list of colors.
scatter_kwargs : dict (default: None)

Keyword arguments for underlying matplotlib scatter function.
contourf_kwargs : dict (default: None)

Keyword arguments for underlying matplotlib contourf function.
scatter_highlight_kwargs : dict (default: None)

Keyword arguments for underlying matplotlib scatter function.

Returns

ax : matplotlib.axes.Axes object

Examples

For usage examples, please see http://rasbt.github.io/mlxtend/user_guide/plotting/plot_decision_regions/