Add cumprod (rust-ndarray#1491)

Author: NewBornRustacean

src/numeric/impl_numeric.rs

@@ -10,7 +10,7 @@
 use num_traits::Float;
 use num_traits::One;
 use num_traits::{FromPrimitive, Zero};
-use std::ops::{Add, Div, Mul, Sub};
+use std::ops::{Add, Div, Mul, MulAssign, Sub};
 
 use crate::imp_prelude::*;
 use crate::numeric_util;
@@ -97,6 +97,45 @@ where D: Dimension
         sum
     }
 
+    /// Return the cumulative product of elements along a given axis.
+    ///
+    /// ```
+    /// use ndarray::{arr2, Axis};
+    ///
+    /// let a = arr2(&[[1., 2., 3.],
+    ///                [4., 5., 6.]]);
+    ///
+    /// // Cumulative product along rows (axis 0)
+    /// assert_eq!(
+    ///     a.cumprod(Axis(0)),
+    ///     arr2(&[[1., 2., 3.],
+    ///           [4., 10., 18.]])
+    /// );
+    ///
+    /// // Cumulative product along columns (axis 1)
+    /// assert_eq!(
+    ///     a.cumprod(Axis(1)),
+    ///     arr2(&[[1., 2., 6.],
+    ///           [4., 20., 120.]])
+    /// );
+    /// ```
+    ///
+    /// **Panics** if `axis` is out of bounds.
+    #[track_caller]
+    pub fn cumprod(&self, axis: Axis) -> Array<A, D>
+    where
+        A: Clone + Mul<Output = A> + MulAssign,
+        D: Dimension + RemoveAxis,
+    {
+        if axis.0 >= self.ndim() {
+            panic!("axis is out of bounds for array of dimension");
+        }
+
+        let mut result = self.to_owned();
+        result.accumulate_axis_inplace(axis, |prev, curr| *curr *= prev.clone());
+        result
+    }
+
     /// Return variance of elements in the array.
     ///
     /// The variance is computed using the [Welford one-pass

tests/numeric.rs

@@ -75,6 +75,76 @@ fn sum_mean_prod_empty()
     assert_eq!(a, None);
 }
 
+#[test]
+fn test_cumprod_1d()
+{
+    let a = array![1, 2, 3, 4];
+    let result = a.cumprod(Axis(0));
+    assert_eq!(result, array![1, 2, 6, 24]);
+}
+
+#[test]
+fn test_cumprod_2d()
+{
+    let a = array![[1, 2], [3, 4]];
+
+    let result_axis0 = a.cumprod(Axis(0));
+    assert_eq!(result_axis0, array![[1, 2], [3, 8]]);
+
+    let result_axis1 = a.cumprod(Axis(1));
+    assert_eq!(result_axis1, array![[1, 2], [3, 12]]);
+}
+
+#[test]
+fn test_cumprod_3d()
+{
+    let a = array![[[1, 2], [3, 4]], [[5, 6], [7, 8]]];
+
+    let result_axis0 = a.cumprod(Axis(0));
+    assert_eq!(result_axis0, array![[[1, 2], [3, 4]], [[5, 12], [21, 32]]]);
+
+    let result_axis1 = a.cumprod(Axis(1));
+    assert_eq!(result_axis1, array![[[1, 2], [3, 8]], [[5, 6], [35, 48]]]);
+
+    let result_axis2 = a.cumprod(Axis(2));
+    assert_eq!(result_axis2, array![[[1, 2], [3, 12]], [[5, 30], [7, 56]]]);
+}
+
+#[test]
+fn test_cumprod_empty()
+{
+    // For 2D empty array
+    let b: Array2<i32> = Array2::zeros((0, 0));
+    let result_axis0 = b.cumprod(Axis(0));
+    assert_eq!(result_axis0, Array2::zeros((0, 0)));
+    let result_axis1 = b.cumprod(Axis(1));
+    assert_eq!(result_axis1, Array2::zeros((0, 0)));
+}
+
+#[test]
+fn test_cumprod_1_element()
+{
+    // For 1D array with one element
+    let a = array![5];
+    let result = a.cumprod(Axis(0));
+    assert_eq!(result, array![5]);
+
+    // For 2D array with one element
+    let b = array![[5]];
+    let result_axis0 = b.cumprod(Axis(0));
+    let result_axis1 = b.cumprod(Axis(1));
+    assert_eq!(result_axis0, array![[5]]);
+    assert_eq!(result_axis1, array![[5]]);
+}
+
+#[test]
+#[should_panic(expected = "axis is out of bounds for array of dimension")]
+fn test_cumprod_axis_out_of_bounds()
+{
+    let a = array![[1, 2], [3, 4]];
+    let _result = a.cumprod(Axis(2));
+}
+
 #[test]
 #[cfg(feature = "std")]
 fn var()