Plotting SVM predictions using matplotlib and sklearn

svmflag.py

import numpy as np
import pylab as pl
import pandas as pd

from sklearn import svm
from sklearn import linear_model
from sklearn import tree

from sklearn.metrics import confusion_matrix

x_min, x_max = 0, 15
y_min, y_max = 0, 10
step = .1
# to plot the boundary, we're going to create a matrix of every possible point
# then label each point as a wolf or cow using our classifier
xx, yy = np.meshgrid(np.arange(x_min, x_max, step), np.arange(y_min, y_max, step))

df = pd.DataFrame(data={'x': xx.ravel(), 'y': yy.ravel()})

df['color_gauge'] = (df.x-7.5)**2 + (df.y-5)**2
df['color'] = df.color_gauge.apply(lambda x: "red" if x <= 15 else "green")
df['color_as_int'] = df.color.apply(lambda x: 0 if x=="red" else 1)

print "Points on flag:"
print df.groupby('color').size()
print

figure = 1

# plot a figure for the entire dataset
for color in df.color.unique():
    idx = df.color==color
    pl.subplot(2, 2, figure)
    pl.scatter(df[idx].x, df[idx].y, color=color)
    pl.title('Actual')


train_idx = df.x < 10

train = df[train_idx]
test = df[-train_idx]


print "Training Set Size: %d" % len(train)
print "Test Set Size: %d" % len(test)

# train using the x and y position coordiantes
cols = ["x", "y"]

clfs = {
    "SVM": svm.SVC(degree=0.5),
    "Logistic" : linear_model.LogisticRegression(),
    "Decision Tree": tree.DecisionTreeClassifier()
}


# racehorse different classifiers and plot the results
for clf_name, clf in clfs.iteritems():
    figure += 1

    # train the classifier
    clf.fit(train[cols], train.color_as_int)

    # get the predicted values from the test set
    test['predicted_color_as_int'] = clf.predict(test[cols])
    test['pred_color'] = test.predicted_color_as_int.apply(lambda x: "red" if x==0 else "green")
    
    # create a new subplot on the plot
    pl.subplot(2, 2, figure)
    # plot each predicted color
    for color in test.pred_color.unique():
        # plot only rows where pred_color is equal to color
        idx = test.pred_color==color
        pl.scatter(test[idx].x, test[idx].y, color=color)

    # plot the training set as well
    for color in train.color.unique():
        idx = train.color==color
        pl.scatter(train[idx].x, train[idx].y, color=color)

    # add a dotted line to show the boundary between the training and test set
    # (everything to the right of the line is in the test set)
    #this plots a vertical line
    train_line_y = np.linspace(y_min, y_max) #evenly spaced array from 0 to 10
    train_line_x = np.repeat(10, len(train_line_y)) #repeat 10 (threshold for traininset) n times
    # add a black, dotted line to the subplot
    pl.plot(train_line_x, train_line_y, 'k--', color="black")
    
    pl.title(clf_name)

    print "Confusion Matrix for %s:" % clf_name
    print confusion_matrix(test.color, test.pred_color)
pl.show()