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Multinomial and One-vs-Rest Logistic Regression in Scikit-learn

Plot decision surface of multinomial and One-vs-Rest Logistic Regression. The hyperplanes corresponding to the three One-vs-Rest (OVR) classifiers are represented by the dashed lines.

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Version

In [1]:
import sklearn
sklearn.__version__
Out[1]:
'0.18.1'

Imports

This tutorial imports make_blobs and LogisticRegression.

In [2]:
print(__doc__)

import plotly.plotly as py
import plotly.graph_objs as go
from plotly import tools

import numpy as np
import matplotlib.pyplot as plt
from sklearn.datasets import make_blobs
from sklearn.linear_model import LogisticRegression
Automatically created module for IPython interactive environment

Calculations

In [3]:
# make 3-class dataset for classification
centers = [[-5, 0], [0, 1.5], [5, -1]]
X, y = make_blobs(n_samples=1000, centers=centers, random_state=40)
transformation = [[0.4, 0.2], [-0.4, 1.2]]
X = np.dot(X, transformation)
fignum = 1
colors = ['blue', 'red', 'yellow']

Plot Results

In [4]:
def matplotlib_to_plotly(cmap, pl_entries):
    h = 1.0/(pl_entries-1)
    pl_colorscale = []
    
    for k in range(pl_entries):
        C = map(np.uint8, np.array(cmap(k*h)[:3])*255)
        pl_colorscale.append([k*h, 'rgb'+str((C[0], C[1], C[2]))])
        
    return pl_colorscale

cmap = matplotlib_to_plotly(plt.cm.Paired, 4)
In [5]:
fig = tools.make_subplots(rows=1, cols=2,
                          print_grid=False,
                          subplot_titles=('Decision surface of LogisticRegression (multinomial)',
                                          'Decision surface of LogisticRegression (ovr)'))

for multi_class in ('multinomial', 'ovr'):
    clf = LogisticRegression(solver='sag', max_iter=100, random_state=42,
                             multi_class=multi_class).fit(X, y)

    # print the training scores
    print("training score : %.3f (%s)" % (clf.score(X, y), multi_class))

    # create a mesh to plot in
    h = .02  # step size in the mesh
    x_min, x_max = X[:, 0].min() - 1, X[:, 0].max() + 1
    y_min, y_max = X[:, 1].min() - 1, X[:, 1].max() + 1
    x_ = np.arange(x_min, x_max, h)
    y_ =  np.arange(y_min, y_max, h)
    xx, yy = np.meshgrid(x_, y_)

    # Plot the decision boundary. For that, we will assign a color to each
    # point in the mesh [x_min, x_max]x[y_min, y_max].
    Z = clf.predict(np.c_[xx.ravel(), yy.ravel()])
    # Put the result into a color plot
    Z = Z.reshape(xx.shape)
    
    trace = go.Contour(x=x_, y=y_, z=Z, 
                       colorscale=cmap, showscale=False)
    fig.append_trace(trace, 1, fignum)
    
    # Plot also the training points
   
    for i, color in zip(clf.classes_, colors):
        idx = np.where(y == i)
        trace = go.Scatter(x=X[idx, 0][0], y=X[idx, 1][0],
                           mode='markers',
                           marker=dict(color=color,
                                       line=dict(color='black', width=1))
                          )
        fig.append_trace(trace, 1, fignum)

    # Plot the three one-against-all classifiers
    coef = clf.coef_
    intercept = clf.intercept_

    def plot_hyperplane(c, color):
        def line(x0):
            return (-(x0 * coef[c, 0]) - intercept[c]) / coef[c, 1]
        trace = go.Scatter(x=[x_min, x_max], y=[line(x_min), line(x_max)],
                           mode='lines', 
                           line=dict(color=color, dash='dash'))
        return trace

    for i, color in zip(clf.classes_, colors):
        trace = plot_hyperplane(i, color)
        fig.append_trace(trace, 1, fignum)
        
    fignum += 1
training score : 0.995 (multinomial)
training score : 0.976 (ovr)
In [6]:
fig['layout']['xaxis1'].update(range=[min(x_), max(x_)])
fig['layout']['xaxis2'].update(range=[min(x_), max(x_)])
fig['layout']['yaxis1'].update(range=[min(y_), max(y_)])
fig['layout']['yaxis2'].update(range=[min(y_), max(y_)])
fig['layout'].update(showlegend=False)

py.iplot(fig)
Out[6]:

License

Authors:

    Tom Dupre la Tour <tom.dupre-la-tour@m4x.org>

License:

    BSD 3 clause
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