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scipy.sparse.

# safely_cast_index_arrays

scipy.sparse.safely_cast_index_arrays(A, idx_dtype=<class 'numpy.int32'>, msg='')

  Safely cast sparse array indices to idx_dtype.

  Check the shape of A to determine if it is safe to cast its index arrays to dtype idx_dtype. If any dimension in shape is larger than fits in the dtype, casting is unsafe so raise `ValueError`. If safe, cast the index arrays to idx_dtype and return the result without changing the input A. The caller can assign results to A attributes if desired or use the recast index arrays directly.

  Unless downcasting is needed, the original index arrays are returned. You can test e.g. `A.indptr is new_indptr` to see if downcasting occurred.

  Added in version 1.15.0.

  Parameters:
    A sparse array or matrix

      The array for which index arrays should be downcast.

    idx_dtype dtype

      Desired dtype. Should be an integer dtype (default: `np.int32`). Most of scipy.sparse uses either int64 or int32.

    msg string, optional

      A string to be added to the end of the ValueError message if the array shape is too big to fit in idx_dtype. The error message is `f"<index> values too large for {msg}"` It should indicate why the downcasting is needed, e.g. “SuperLU”, and defaults to f”dtype {idx_dtype}”.

  Returns:
    idx_arrays ndarray or tuple of ndarrays

      Based on `A.format`, index arrays are returned after casting to idx_dtype. For CSC/CSR, returns `(indices, indptr)`. For COO, returns `coords`. For DIA, returns `offsets`. For BSR, returns `(indices, indptr)`.

  Raises:
    ValueError

      If the array has shape that would not fit in the new dtype, or if the sparse format does not use index arrays.

  Examples

      >>> import numpy as np
      >>> from scipy import sparse
      >>> data = [3]
      >>> coords = (np.array([3]), np.array([1]))  # Note: int64 arrays
      >>> A = sparse.coo_array((data, coords))
      >>> A.coords[0].dtype
      dtype('int64')

      >>> # rescast after construction, raising exception if shape too big
      >>> coords = sparse.safely_cast_index_arrays(A, np.int32)
      >>> A.coords[0] is coords[0]  # False if casting is needed
      False
      >>> A.coords = coords  # set the index dtype of A
      >>> A.coords[0].dtype
      dtype('int32')