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Logistic Regression 3-Class Classifier in Scikit-learn

Show below is a logistic-regression classifiers decision boundaries on the iris dataset. The datapoints are colored according to their labels.

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Version

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

Imports

In [2]:
import plotly.plotly as py
import plotly.graph_objs as go

import numpy as np
import matplotlib.pyplot as plt
from sklearn import linear_model, datasets

Calculaions

Import some data to play with

In [3]:
iris = datasets.load_iris()
X = iris.data[:, :2]  # we only take the first two features.
Y = iris.target

h = .02  # step size in the mesh

logreg = linear_model.LogisticRegression(C=1e5)

we create an instance of Neighbours Classifier and fit the data.

In [4]:
logreg.fit(X, Y)
Out[4]:
LogisticRegression(C=100000.0, class_weight=None, dual=False,
          fit_intercept=True, intercept_scaling=1, max_iter=100,
          multi_class='ovr', n_jobs=1, penalty='l2', random_state=None,
          solver='liblinear', tol=0.0001, verbose=0, warm_start=False)

Plot the decision boundary.

In [5]:
# For that, we will assign a color to each
# point in the mesh [x_min, x_max]x[y_min, y_max].
x_min, x_max = X[:, 0].min() - .5, X[:, 0].max() + .5
y_min, y_max = X[:, 1].min() - .5, X[:, 1].max() + .5
x_ = np.arange(x_min, x_max, h)
y_ = np.arange(y_min, y_max, h)
xx, yy = np.meshgrid(x_, y_)
Z = logreg.predict(np.c_[xx.ravel(), yy.ravel()])

Put the result into a color plot

In [6]:
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 [7]:
Z = Z.reshape(xx.shape)

trace = go.Heatmap(x=x_, y=y_, z=Z,
                   colorscale=cmap,
                   showscale=False,
                  )

Plot the training points

In [8]:
trace1 = go.Scatter(x=X[:, 0], y=X[:, 1],
                    mode='markers',
                    marker=dict(color=X[:, 0],
                                colorscale=cmap,
                                showscale=False,
                                line=dict(color='black', width=1))
                   )
In [9]:
layout = go.Layout(xaxis=dict(title='Sepal length', ticks='',
                              showticklabels=False),
                   yaxis=dict(title='Sepal width', ticks='',
                              showticklabels=False)
                  )

fig = go.Figure(data=[trace, trace1], layout=layout)
In [10]:
py.iplot(fig)
Out[10]:

License

Code source:

        Gaƫl Varoquaux

Modified for documentation by Jaques Grobler

License:

        BSD 3 clause
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