Complete grid search params (#166)

* grid search draft

* hyperparam search for linear estimators

* grid search for ensembles

* support grid search for more algos

* grid search for unsupervised algos

* minor cleanup

src/tree/decision_tree_classifier.rs

@@ -201,6 +201,144 @@ impl Default for DecisionTreeClassifierParameters {
     }
 }
 
+/// DecisionTreeClassifier grid search parameters
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+#[derive(Debug, Clone)]
+pub struct DecisionTreeClassifierSearchParameters {
+    /// Split criteria to use when building a tree. See [Decision Tree Classifier](../../tree/decision_tree_classifier/index.html)
+    pub criterion: Vec<SplitCriterion>,
+    /// Tree max depth. See [Decision Tree Classifier](../../tree/decision_tree_classifier/index.html)
+    pub max_depth: Vec<Option<u16>>,
+    /// The minimum number of samples required to be at a leaf node. See [Decision Tree Classifier](../../tree/decision_tree_classifier/index.html)
+    pub min_samples_leaf: Vec<usize>,
+    /// The minimum number of samples required to split an internal node. See [Decision Tree Classifier](../../tree/decision_tree_classifier/index.html)
+    pub min_samples_split: Vec<usize>,
+}
+
+/// DecisionTreeClassifier grid search iterator
+pub struct DecisionTreeClassifierSearchParametersIterator {
+    decision_tree_classifier_search_parameters: DecisionTreeClassifierSearchParameters,
+    current_criterion: usize,
+    current_max_depth: usize,
+    current_min_samples_leaf: usize,
+    current_min_samples_split: usize,
+}
+
+impl IntoIterator for DecisionTreeClassifierSearchParameters {
+    type Item = DecisionTreeClassifierParameters;
+    type IntoIter = DecisionTreeClassifierSearchParametersIterator;
+
+    fn into_iter(self) -> Self::IntoIter {
+        DecisionTreeClassifierSearchParametersIterator {
+            decision_tree_classifier_search_parameters: self,
+            current_criterion: 0,
+            current_max_depth: 0,
+            current_min_samples_leaf: 0,
+            current_min_samples_split: 0,
+        }
+    }
+}
+
+impl Iterator for DecisionTreeClassifierSearchParametersIterator {
+    type Item = DecisionTreeClassifierParameters;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.current_criterion
+            == self
+                .decision_tree_classifier_search_parameters
+                .criterion
+                .len()
+            && self.current_max_depth
+                == self
+                    .decision_tree_classifier_search_parameters
+                    .max_depth
+                    .len()
+            && self.current_min_samples_leaf
+                == self
+                    .decision_tree_classifier_search_parameters
+                    .min_samples_leaf
+                    .len()
+            && self.current_min_samples_split
+                == self
+                    .decision_tree_classifier_search_parameters
+                    .min_samples_split
+                    .len()
+        {
+            return None;
+        }
+
+        let next = DecisionTreeClassifierParameters {
+            criterion: self.decision_tree_classifier_search_parameters.criterion
+                [self.current_criterion]
+                .clone(),
+            max_depth: self.decision_tree_classifier_search_parameters.max_depth
+                [self.current_max_depth],
+            min_samples_leaf: self
+                .decision_tree_classifier_search_parameters
+                .min_samples_leaf[self.current_min_samples_leaf],
+            min_samples_split: self
+                .decision_tree_classifier_search_parameters
+                .min_samples_split[self.current_min_samples_split],
+        };
+
+        if self.current_criterion + 1
+            < self
+                .decision_tree_classifier_search_parameters
+                .criterion
+                .len()
+        {
+            self.current_criterion += 1;
+        } else if self.current_max_depth + 1
+            < self
+                .decision_tree_classifier_search_parameters
+                .max_depth
+                .len()
+        {
+            self.current_criterion = 0;
+            self.current_max_depth += 1;
+        } else if self.current_min_samples_leaf + 1
+            < self
+                .decision_tree_classifier_search_parameters
+                .min_samples_leaf
+                .len()
+        {
+            self.current_criterion = 0;
+            self.current_max_depth = 0;
+            self.current_min_samples_leaf += 1;
+        } else if self.current_min_samples_split + 1
+            < self
+                .decision_tree_classifier_search_parameters
+                .min_samples_split
+                .len()
+        {
+            self.current_criterion = 0;
+            self.current_max_depth = 0;
+            self.current_min_samples_leaf = 0;
+            self.current_min_samples_split += 1;
+        } else {
+            self.current_criterion += 1;
+            self.current_max_depth += 1;
+            self.current_min_samples_leaf += 1;
+            self.current_min_samples_split += 1;
+        }
+
+        Some(next)
+    }
+}
+
+impl Default for DecisionTreeClassifierSearchParameters {
+    fn default() -> Self {
+        let default_params = DecisionTreeClassifierParameters::default();
+
+        DecisionTreeClassifierSearchParameters {
+            criterion: vec![default_params.criterion],
+            max_depth: vec![default_params.max_depth],
+            min_samples_leaf: vec![default_params.min_samples_leaf],
+            min_samples_split: vec![default_params.min_samples_split],
+        }
+    }
+}
+
 impl<T: RealNumber> Node<T> {
     fn new(index: usize, output: usize) -> Self {
         Node {
@@ -651,6 +789,29 @@ mod tests {
     use super::*;
     use crate::linalg::naive::dense_matrix::DenseMatrix;
 
+    #[test]
+    fn search_parameters() {
+        let parameters = DecisionTreeClassifierSearchParameters {
+            max_depth: vec![Some(10), Some(100)],
+            min_samples_split: vec![1, 2],
+            ..Default::default()
+        };
+        let mut iter = parameters.into_iter();
+        let next = iter.next().unwrap();
+        assert_eq!(next.max_depth, Some(10));
+        assert_eq!(next.min_samples_split, 1);
+        let next = iter.next().unwrap();
+        assert_eq!(next.max_depth, Some(100));
+        assert_eq!(next.min_samples_split, 1);
+        let next = iter.next().unwrap();
+        assert_eq!(next.max_depth, Some(10));
+        assert_eq!(next.min_samples_split, 2);
+        let next = iter.next().unwrap();
+        assert_eq!(next.max_depth, Some(100));
+        assert_eq!(next.min_samples_split, 2);
+        assert!(iter.next().is_none());
+    }
+
     #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test::wasm_bindgen_test)]
     #[test]
     fn gini_impurity() {