feat: adds train/test split function; fixes bug in random forest

src/tree/decision_tree_classifier.rs

@@ -67,6 +67,7 @@ use std::default::Default;
 use std::fmt::Debug;
 use std::marker::PhantomData;
 
+use rand::seq::SliceRandom;
 use serde::{Deserialize, Serialize};
 
 use crate::algorithm::sort::quick_sort::QuickArgSort;
@@ -431,6 +432,10 @@ impl<T: RealNumber> DecisionTreeClassifier<T> {
             variables[i] = i;
         }
 
+        if mtry < n_attr {
+            variables.shuffle(&mut rand::thread_rng());
+        }
+
         for j in 0..mtry {
             self.find_best_split(
                 visitor,