[math] Unique columns as array for CSR sparse matrix

src/sparse_matrix_utils.c

@@ -16,4 +16,49 @@ sparse_matrix_t *sparse_matrix_new_from_matrix(matrix_t *matrix) {
         sparse_matrix_finalize_row(sparse);
     }
     return sparse;
-}
+}
+
+
+bool sparse_matrix_add_unique_columns(sparse_matrix_t *matrix, khash_t(int_set) *unique_columns, uint32_array *array) {
+    size_t n = matrix->indices->n;
+    uint32_t *indices = matrix->indices->a;
+
+    kh_clear(int_set, unique_columns);
+
+    size_t i;
+
+    for (i = 0; i < n; i++) {
+        uint32_t col = indices[i];
+
+        int ret;
+        kh_put(int_set, unique_columns, (khint_t)col, &ret);
+        if (ret < 0) {
+            return false;
+        }
+    }
+
+    uint32_array_clear(array);
+    uint32_array_resize(array, kh_size(unique_columns));
+
+    khint_t k;
+
+    kh_foreach_key(unique_columns, k, {
+        uint32_array_push(array, (uint32_t)k);
+    })
+
+    return true;
+}
+
+uint32_array *sparse_matrix_unique_columns(sparse_matrix_t *matrix) {
+    khash_t(int_set) *unique_columns = kh_init(int_set);
+    uint32_array *ret = uint32_array_new();
+
+    if (sparse_matrix_add_unique_columns(matrix, unique_columns, ret)) {
+        kh_destroy(int_set, unique_columns);
+        return ret;
+    }
+
+    kh_destroy(int_set, unique_columns);
+    uint32_array_destroy(ret);
+    return NULL;
+}