Find the best split threshold 'thres' that divides feature/variable 'xj' into low (<= 'thesh') and high (> 'thres') values such that weighted entropy is minimized.
Find the best split threshold 'thres' that divides feature/variable 'xj' into low (<= 'thesh') and high (> 'thres') values such that weighted entropy is minimized.
Value parameters
idx_
the index positions within x (if null, use all index positions)