public class ChiSqSelector
Creates a ChiSquared feature selector.
param: numTopFeatures number of features that selector will select
(ordered by statistic value descending)
Note that if the number of features is less than numTopFeatures,
then this will select all features.
data - an RDD[LabeledPoint] containing the labeled dataset with categorical features.
Real-valued features will be treated as categorical for each distinct value.
Apply feature discretizer before using this function.