Add tests for mean, variance, and standard deviation calculations in vertical and horizontal directions

src/compute/stats/descriptive.rs

@@ -26,7 +26,8 @@ pub fn variance(x: &Matrix<f64>) -> f64 {
 
 fn _variance_axis(x: &Matrix<f64>, axis: Axis) -> Matrix<f64> {
     match axis {
-        Axis::Row => { // Calculate variance for each column (vertical variance)
+        Axis::Row => {
+            // Calculate variance for each column (vertical variance)
             let num_rows = x.rows() as f64;
             let mean_of_cols = mean_vertical(x); // 1 x cols matrix
             let mut result_data = vec![0.0; x.cols()];
@@ -42,7 +43,8 @@ fn _variance_axis(x: &Matrix<f64>, axis: Axis) -> Matrix<f64> {
             }
             Matrix::from_vec(result_data, 1, x.cols())
         }
-        Axis::Col => { // Calculate variance for each row (horizontal variance)
+        Axis::Col => {
+            // Calculate variance for each row (horizontal variance)
             let num_cols = x.cols() as f64;
             let mean_of_rows = mean_horizontal(x); // rows x 1 matrix
             let mut result_data = vec![0.0; x.rows()];
@@ -224,4 +226,58 @@ mod tests {
         let x = Matrix::from_vec(data, 1, 3);
         percentile(&x, 101.0);
     }
+
+    #[test]
+    fn test_mean_vertical_horizontal() {
+        // 2x3 matrix:
+        let data = vec![1.0, 4.0, 2.0, 5.0, 3.0, 6.0];
+        let x = Matrix::from_vec(data, 2, 3);
+
+        // Vertical means (per column): [(1+4)/2, (2+5)/2, (3+6)/2]
+        let mv = mean_vertical(&x);
+        assert!((mv.get(0, 0) - 2.5).abs() < EPSILON);
+        assert!((mv.get(0, 1) - 3.5).abs() < EPSILON);
+        assert!((mv.get(0, 2) - 4.5).abs() < EPSILON);
+
+        // Horizontal means (per row): [(1+2+3)/3, (4+5+6)/3]
+        let mh = mean_horizontal(&x);
+        assert!((mh.get(0, 0) - 2.0).abs() < EPSILON);
+        assert!((mh.get(1, 0) - 5.0).abs() < EPSILON);
+    }
+
+    #[test]
+    fn test_variance_vertical_horizontal() {
+        let data = vec![1.0, 4.0, 2.0, 5.0, 3.0, 6.0];
+        let x = Matrix::from_vec(data, 2, 3);
+
+        // Vertical variances (per column): each is ((v - mean)^2 summed / 2)
+        // cols: {1,4}, {2,5}, {3,6} all give 2.25
+        let vv = variance_vertical(&x);
+        for c in 0..3 {
+            assert!((vv.get(0, c) - 2.25).abs() < EPSILON);
+        }
+
+        // Horizontal variances (per row): rows [1,2,3] and [4,5,6] both give 2/3
+        let vh = variance_horizontal(&x);
+        assert!((vh.get(0, 0) - (2.0 / 3.0)).abs() < EPSILON);
+        assert!((vh.get(1, 0) - (2.0 / 3.0)).abs() < EPSILON);
+    }
+
+    #[test]
+    fn test_stddev_vertical_horizontal() {
+        let data = vec![1.0, 4.0, 2.0, 5.0, 3.0, 6.0];
+        let x = Matrix::from_vec(data, 2, 3);
+
+        // Stddev is sqrt of variance
+        let sv = stddev_vertical(&x);
+        for c in 0..3 {
+            assert!((sv.get(0, c) - 1.5).abs() < EPSILON);
+        }
+
+        let sh = stddev_horizontal(&x);
+        // sqrt(2/3) ≈ 0.816497
+        let expected = (2.0 / 3.0 as f64).sqrt();
+        assert!((sh.get(0, 0) - expected).abs() < EPSILON);
+        assert!((sh.get(1, 0) - expected).abs() < EPSILON);
+    }
 }