add scipy converstion

lenskit/util/csmatrix.pyi

@@ -1,5 +1,6 @@
 import numpy as np
 import numpy.typing as npt
+from scipy.sparse import csr_array
 
 class CSMatrix:
     nrows: int
@@ -19,3 +20,5 @@ class CSMatrix:
         vs: npt.NDArray[np.float64],
     ): ...
     def row_ep(self, row: int) -> tuple[int, int]: ...
+    @staticmethod
+    def from_scipy(matrix: csr_array) -> CSMatrix: ...

lenskit/util/csmatrix.pyx

@@ -14,6 +14,12 @@ cdef class CSMatrix:
         self.values = vs
         self.nnz = self.rowptr[nr]
 
+    @staticmethod
+    def from_scipy(m):
+        nr, nc = m.shape
+
+        return CSMatrix(nr, nc, m.indptr, m.indices, m.data)
+
     cpdef (int,int) row_ep(self, row):
         if row < 0 or row >= self.nrows:
             raise IndexError(f"invalid row {row} for {self.nrows}x{self.ncols} matrix")

tests/test_csmatrix.py

@@ -42,12 +42,21 @@ def test_init_matrix(m: sps.csr_array):
     assert m2.nnz == m.nnz
 
 
+@given(sparse_matrices())
+def test_from_scipy(m: sps.csr_array):
+    print(m.shape, m.nnz, m.indptr.dtype, m.indices.dtype)
+    m2 = CSMatrix.from_scipy(m)
+
+    assert m2.nrows == m.shape[0]
+    assert m2.ncols == m.shape[1]
+    assert m2.nnz == m.nnz
+
+
 @given(sparse_matrices())
 def test_csm_row_ep(m: sps.csr_array):
-    nr, nc = m.shape
-    m2 = CSMatrix(nr, nc, m.indptr, m.indices, m.data)
+    m2 = CSMatrix.from_scipy(m)
 
-    for i in range(nr):
+    for i in range(m2.nrows):
         sp, ep = m2.row_ep(i)
         assert sp == m2.rowptr[i]
         assert ep == m2.rowptr[i + 1]