deviation: Implement sq_l2_dist

Author: munckymagik

src/deviation.rs

@@ -1,4 +1,6 @@
 use ndarray::{ArrayBase, Data, Dimension, Zip};
+use num_traits::sign::Signed;
+use std::ops::AddAssign;
 
 /// Extension trait for `ArrayBase` providing functions
 /// to compute different deviation measures.
@@ -14,6 +16,10 @@ where
     fn count_neq(&self, other: &ArrayBase<S, D>) -> usize
     where
         A: PartialEq;
+
+    fn sq_l2_dist(&self, other: &ArrayBase<S, D>) -> A
+    where
+        A: AddAssign + Copy + Signed;
 }
 
 impl<A, S, D> DeviationExt<A, S, D> for ArrayBase<S, D>
@@ -42,6 +48,19 @@ where
     {
         self.len() - self.count_eq(other)
     }
+
+    fn sq_l2_dist(&self, other: &ArrayBase<S, D>) -> A
+    where
+        A: AddAssign + Copy + Signed,
+    {
+        let mut r = A::zero();
+
+        Zip::from(self).and(other).apply(|&a, &b| {
+            r += (a - b).abs();
+        });
+
+        r
+    }
 }
 
 #[cfg(test)]
@@ -74,4 +93,17 @@ mod tests {
         assert_eq!(b.count_neq(&c), 7);
         assert_eq!(d.count_neq(&e), 2);
     }
+
+    #[test]
+    fn test_sq_l2_dist() {
+        let a = array![1., 2., 3., 4., 5., 6., 7.];
+        let b = array![1., 3., 3., 4., 6., 7., 8.];
+
+        assert_eq!(a.sq_l2_dist(&b), (&a - &b).mapv(f64::abs).sum());
+
+        let a = array![[1, 2], [3, 4], [5, 6]];
+        let b = array![[1, 3], [3, 4], [6, 7]];
+
+        assert_eq!(a.sq_l2_dist(&b), (&a - &b).mapv(i32::abs).sum());
+    }
 }