Random Forest with scikit-learn

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Random Forest Classfier

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Random Forest Classfier is one of the ensemble method machine learning algorithm. It's a variance of decision tree. It uses different subset and different selection of features and using weighted regression(by voting).

This is the snapshot which I taken from mathematicalmonk's youtube video. You can find the url link of the video at the bottom of this page.

So suppose we have training examples, and we call that set of training examples contains X(set of features) and Y(the value which we are trying to predict) and we assign that to variable of D.

Here we choose B, as the number of estimators that we defined. What I mean is we set B-count of how many we want to keep random sampling from our fullset of D over and over again. Then we're taking bootstrapt sample, taking random sample from D, and assign it to variable Di.

Using Di to construct node tree of Ti, here the tree is what I refer as decision tree. At each node, we pick, again, random features. Then we perform features split, just on the features picked earlier, as we do in decision tree.

Now the benefit of Random Forest, is that because we randomly select samples (this is why Random Forest is called bagging), and randomly select features, we have bunch of trees, depending of B, and each of those is a predictive model of learning algorithm. This is what we called ensemble learning algorithm. Next of all given x in the future, y will be decided by taking vote from all the tree that we have. Because Random Forest is ensemble learning, it have some nice overfitting controlling, because we're taking vote from our group of learning algorithms, not just one learning algorithm, which prone to overfitting.

In [17]:
%pylab inline
Populating the interactive namespace from numpy and matplotlib
In [16]:
%load your_algorithm.py
In [18]:
#!/usr/bin/python

import matplotlib.pyplot as plt
from prep_terrain_data import makeTerrainData
from class_vis import prettyPicture

features_train, labels_train, features_test, labels_test = makeTerrainData()


### the training data (features_train, labels_train) have both "fast" and "slow" points mixed
### in together--separate them so we can give them different colors in the scatterplot,
### and visually identify them
grade_fast = [features_train[ii][0] for ii in range(0, len(features_train)) if labels_train[ii]==0]
bumpy_fast = [features_train[ii][1] for ii in range(0, len(features_train)) if labels_train[ii]==0]
grade_slow = [features_train[ii][0] for ii in range(0, len(features_train)) if labels_train[ii]==1]
bumpy_slow = [features_train[ii][1] for ii in range(0, len(features_train)) if labels_train[ii]==1]


#### initial visualization
plt.xlim(0.0, 1.0)
plt.ylim(0.0, 1.0)
plt.scatter(bumpy_fast, grade_fast, color = "b", label="fast")
plt.scatter(grade_slow, bumpy_slow, color = "r", label="slow")
plt.legend()
plt.xlabel("bumpiness")
plt.ylabel("grade")
plt.show()
#################################################################################


### your code here!  name your classifier object clf if you want the 
### visualization code (prettyPicture) to show you the decision boundary

try:
    prettyPicture(clf, features_test, labels_test)
except NameError:
    pass
In [19]:
from sklearn.ensemble import RandomForestClassifier
In [20]:
clf = RandomForestClassifier(min_samples_split=50)
In [21]:
clf.fit(features_train,labels_train)
Out[21]:
RandomForestClassifier(bootstrap=True, compute_importances=None,
            criterion='gini', max_depth=None, max_features='auto',
            max_leaf_nodes=None, min_density=None, min_samples_leaf=1,
            min_samples_split=50, n_estimators=10, n_jobs=1,
            oob_score=False, random_state=None, verbose=0)
In [22]:
clf.score(features_test,labels_test)
Out[22]:
0.92400000000000004
In [23]:
prettyPicture(clf,features_test,labels_test)
In [ ]: