diff --git a/src/feature_selection.odin b/src/feature_selection.odin
index c22422b..79cdf6a 100644
--- a/src/feature_selection.odin
+++ b/src/feature_selection.odin
@@ -7,6 +7,7 @@ import "core:fmt"
 import "core:math"
 import "core:os"
 import "core:strconv"
+import "base:runtime"
 
 NUMBER_OF_FEATURES :: 100
 DATASET_ROWS :: 1994
@@ -23,7 +24,8 @@ Feature_State :: struct {
 	X_train: [][]f64,
 	X_test: [][]f64,
 	y_train: []f64,
-	y_test: []f64
+	y_test: []f64,
+	selected_indices_buffer: [NUMBER_OF_FEATURES]int,
 }
 
 feature_state: Feature_State
@@ -96,6 +98,12 @@ split_dataset :: proc() {
 }
 
 fitness_features :: proc(chrom: Chromosome) -> f64 {
+    temp_arena: runtime.Arena
+    defer runtime.arena_destroy(&temp_arena)
+    temp_allocator := runtime.arena_allocator(&temp_arena)
+
+    context.allocator = temp_allocator
+
     X_train_selected := select_features(feature_state.X_train, chrom)
     X_test_selected := select_features(feature_state.X_test, chrom)
 
@@ -103,46 +111,35 @@ fitness_features :: proc(chrom: Chromosome) -> f64 {
         return math.F64_MAX
     }
 
-    defer {
-        for row in X_train_selected {delete(row)}
-        for row in X_test_selected {delete(row)}
-        delete(X_train_selected)
-        delete(X_test_selected)
-    }
-
     beta := train_linear_regression(X_train_selected, feature_state.y_train)
-    defer delete(beta)
-
     predictions := predict(X_test_selected, beta)
-    defer delete(predictions)
 
     return rmse(predictions, feature_state.y_test)
 }
 
 // Select columns (features) based on chromosome
-select_features :: proc(X: [][]f64, chrom: Chromosome) -> [][]f64 {
-    selected_indices := make([dynamic]int)
-    defer delete(selected_indices)
-
+select_features :: proc(X: [][]f64, chrom: Chromosome, allocator := context.allocator) -> [][]f64 {
+    // Count selected features inline
+    n_selected := 0
     for i in 0 ..< bit_array.len(chrom) {
         if bit_array.get(chrom, i) {
-            append(&selected_indices, i)
+            feature_state.selected_indices_buffer[n_selected] = i
+            n_selected += 1
         }
     }
 
-    if len(selected_indices) == 0 {
+    if n_selected == 0 {
         return nil
     }
 
     n_rows := len(X)
-    n_features := len(selected_indices)
 
-    result := make([][]f64, n_rows)
+    // Single allocation for all rows
+    result := make([][]f64, n_rows, allocator)
     for i in 0 ..< n_rows {
-        result[i] = make([]f64, n_features)
-        for j in 0 ..< n_features {
-            feat_idx := selected_indices[j]
-            result[i][j] = X[i][feat_idx]
+        result[i] = make([]f64, n_selected, allocator)
+        for j in 0 ..< n_selected {
+            result[i][j] = X[i][feature_state.selected_indices_buffer[j]]
         }
     }