From 9e85c9e2b69fa443da8f12bb51e9d63c0d319517 Mon Sep 17 00:00:00 2001
From: Anton <playwot@rambler.ru>
Date: Sun, 3 Oct 2021 00:56:13 +0200
Subject: [PATCH] CSR/CSC: Provide constructor for unsorted but otherwise valid
 data

---
 nalgebra-sparse/src/csr.rs              | 27 +++++++++++++++++++++++++
 nalgebra-sparse/tests/unit_tests/csr.rs | 23 +++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/nalgebra-sparse/src/csr.rs b/nalgebra-sparse/src/csr.rs
index c64be915..fd39fc75 100644
--- a/nalgebra-sparse/src/csr.rs
+++ b/nalgebra-sparse/src/csr.rs
@@ -170,6 +170,24 @@ impl<T> CsrMatrix<T> {
         Self::try_from_pattern_and_values(pattern, values)
     }
 
+    /// Try to construct a CSR matrix from raw CSR data with unsorted columns.
+    pub fn try_from_unsorted_csr_data(
+        num_rows: usize,
+        num_cols: usize,
+        row_offsets: Vec<usize>,
+        col_indices: Vec<usize>,
+        values: Vec<T>,
+    ) -> Result<Self, SparseFormatError> {
+        let sorted_num_cols: Vec<usize> = row_offsets[0..row_offsets.len() - 1]
+            .iter()
+            .enumerate()
+            .flat_map(|(index, &offset)| {
+                Self::sorted(col_indices[offset..row_offsets[index + 1]].to_vec())
+            })
+            .collect();
+        return Self::try_from_csr_data(num_rows, num_cols, row_offsets, sorted_num_cols, values);
+    }
+
     /// Try to construct a CSR matrix from a sparsity pattern and associated non-zero values.
     ///
     /// Returns an error if the number of values does not match the number of minor indices
@@ -190,6 +208,15 @@ impl<T> CsrMatrix<T> {
         }
     }
 
+    /// Return sorted vector.
+    #[inline]
+    #[must_use]
+    pub fn sorted(row_offsets: Vec<usize>) -> Vec<usize> {
+        let mut sorted = row_offsets.clone();
+        sorted.sort();
+        return sorted;
+    }
+
     /// The number of rows in the matrix.
     #[inline]
     #[must_use]
diff --git a/nalgebra-sparse/tests/unit_tests/csr.rs b/nalgebra-sparse/tests/unit_tests/csr.rs
index dee1ae1e..73d4dd27 100644
--- a/nalgebra-sparse/tests/unit_tests/csr.rs
+++ b/nalgebra-sparse/tests/unit_tests/csr.rs
@@ -171,6 +171,29 @@ fn csr_matrix_valid_data() {
     }
 }
 
+#[test]
+fn csr_matrix_valid_data_unsorted_column_indices() {
+    let csr = CsrMatrix::try_from_unsorted_csr_data(
+        3,
+        4,
+        vec![0, 1, 2, 5],
+        vec![1, 3, 2, 3, 0],
+        vec![5, 4, 1, 1, 4],
+    )
+    .unwrap();
+
+    let expected_csr = CsrMatrix::try_from_csr_data(
+        3,
+        4,
+        vec![0, 1, 2, 5],
+        vec![1, 3, 0, 2, 3],
+        vec![5, 4, 1, 1, 4],
+    )
+    .unwrap();
+
+    assert_eq!(csr, expected_csr);
+}
+
 #[test]
 fn csr_matrix_try_from_invalid_csr_data() {
     {