diff --git a/src/preprocessing/series_encoder.rs b/src/preprocessing/series_encoder.rs
index 438d678..4e9625e 100644
--- a/src/preprocessing/series_encoder.rs
+++ b/src/preprocessing/series_encoder.rs
@@ -8,6 +8,73 @@ use crate::math::num::RealNumber;
 use std::collections::HashMap;
 use std::hash::Hash;
 
+#[derive(Debug, Clone)]
+pub struct CategoryMapper<CategoryType> {
+    category_map: HashMap<CategoryType, usize>,
+    categories: Vec<CategoryType>,
+    num_categories: usize,
+}
+
+impl<'a, CategoryType: 'a + Hash + Eq + Clone> CategoryMapper<CategoryType> {
+    fn fit_to_iter(categories: impl Iterator<Item = CategoryType>) -> Self {
+        let mut category_map: HashMap<CategoryType, usize> = HashMap::new();
+        let mut category_num = 0usize;
+        let mut unique_lables: Vec<CategoryType> = Vec::new();
+
+        for l in categories {
+            if !category_map.contains_key(&l) {
+                category_map.insert(l.clone(), category_num);
+                unique_lables.push(l.clone());
+                category_num += 1;
+            }
+        }
+        Self {
+            category_map,
+            num_categories: category_num,
+            categories: unique_lables,
+        }
+    }
+
+    fn from_category_map(category_map: HashMap<CategoryType, usize>) -> Self {
+        let mut _unique_cat: Vec<(CategoryType, usize)> =
+            category_map.iter().map(|(k, v)| (k.clone(), *v)).collect();
+        _unique_cat.sort_by(|a, b| a.1.cmp(&b.1));
+        let categories: Vec<CategoryType> = _unique_cat.into_iter().map(|a| a.0).collect();
+        Self {
+            num_categories: categories.len(),
+            categories,
+            category_map,
+        }
+    }
+
+    fn from_positional_category_vec(categories: Vec<CategoryType>) -> Self {
+        let category_map: HashMap<CategoryType, usize> = categories
+            .iter()
+            .enumerate()
+            .map(|(v, k)| (k.clone(), v))
+            .collect();
+        Self {
+            num_categories: categories.len(),
+            category_map,
+            categories,
+        }
+    }
+
+    /// Get label num of a category
+    fn get_num(&self, category: &CategoryType) -> Option<&usize> {
+        self.category_map.get(category)
+    }
+
+    /// Return category corresponding to label num
+    fn get_cat(&self, num: usize) -> &CategoryType {
+        &self.categories[num]
+    }
+
+    fn get_categories(&self) -> &[CategoryType] {
+        &self.categories[..]
+    }
+}
+
 /// Make a one-hot encoded vector from a categorical variable
 ///
 /// Example: