Add clear_triplet()

nalgebra-sparse/src/coo.rs

@@ -211,6 +211,26 @@ impl<T> CooMatrix<T> {
         self.values.push(v);
     }
 
+    /// Remove a single triplet from the matrix.
+    ///
+    /// This removes the value `v` from the `i`th row and `j`th column in the matrix.
+    pub fn clear_triplet(&mut self, i: usize, j: usize, v: T) -> Option<(usize, usize, T)>
+    where
+        T: PartialEq,
+    {
+        let triple_idx = self
+            .triplet_iter()
+            .position(|triplet| triplet == (i, j, &v));
+        if let Some(triple_idx) = triple_idx {
+            self.row_indices.remove(triple_idx);
+            self.col_indices.remove(triple_idx);
+            let retv = self.values.remove(triple_idx);
+            Some((i, j, retv))
+        } else {
+            None
+        }
+    }
+
     /// The number of rows in the matrix.
     #[inline]
     #[must_use]

nalgebra-sparse/tests/unit_tests/coo.rs

@@ -226,6 +226,35 @@ fn coo_push_valid_entries() {
     );
 }
 
+#[test]
+fn coo_clear_triplet_valid_entries() {
+    let mut coo = CooMatrix::new(3, 3);
+
+    coo.push(0, 0, 1);
+    coo.push(0, 0, 2);
+    coo.push(2, 2, 3);
+
+    // clear a triplet that is not included
+    let triplet = coo.clear_triplet(0, 0, 0);
+    assert_eq!(triplet, None);
+    assert_eq!(
+        coo.triplet_iter().collect::<Vec<_>>(),
+        vec![(0, 0, &1), (0, 0, &2), (2, 2, &3)]
+    );
+    let triplet = coo.clear_triplet(0, 0, 1);
+    assert_eq!(triplet, Some((0, 0, 1)));
+    assert_eq!(
+        coo.triplet_iter().collect::<Vec<_>>(),
+        vec![(0, 0, &2), (2, 2, &3)]
+    );
+    let triplet = coo.clear_triplet(0, 0, 2);
+    assert_eq!(triplet, Some((0, 0, 2)));
+    assert_eq!(coo.triplet_iter().collect::<Vec<_>>(), vec![(2, 2, &3)]);
+    let triplet = coo.clear_triplet(2, 2, 3);
+    assert_eq!(triplet, Some((2, 2, 3)));
+    assert_eq!(coo.triplet_iter().collect::<Vec<_>>(), vec![]);
+}
+
 #[test]
 fn coo_push_out_of_bounds_entries() {
     {