Set row of csr_matrix

Question

I have a sparse csr_matrix, and I want to change the values of a single row to different values. I can\'t find an easy and efficient implementation however. This is what it

Answer 1

In physicalattraction's answer, the len(new_row) must be equal to A.shape[1] what may not be interesting when adding sparse rows.

So, based on his answer I've came up with a method to set rows in csr while it keeps the sparcity property. Additionally I've added a method to convert dense arrays to sparse arrays (on data, indices format)

def to_sparse(dense_arr):
    sparse = [(data, index) for index, data in enumerate(dense_arr) if data != 0]

    # Convert list of tuples to lists
    sparse = list(map(list, zip(*sparse)))

    # Return data and indices
    return sparse[0], sparse[1]

def set_row_csr_unbounded(A, row_idx, new_row_data, new_row_indices):
    '''
    Replace a row in a CSR sparse matrix A.

    Parameters
    ----------
    A: csr_matrix
        Matrix to change
    row_idx: int
        index of the row to be changed
    new_row_data: np.array
        list of new values for the row of A
    new_row_indices: np.array
        list of indices for new row

    Returns
    -------
    None (the matrix A is changed in place)

    Prerequisites
    -------------
    The row index shall be smaller than the number of rows in A
    Row data and row indices must have the same size
    '''
    assert isspmatrix_csr(A), 'A shall be a csr_matrix'
    assert row_idx < A.shape[0], \
            'The row index ({0}) shall be smaller than the number of rows in A ({1})' \
            .format(row_idx, A.shape[0])

    try:
        N_elements_new_row = len(new_row_data)
    except TypeError:
        msg = 'Argument new_row_data shall be a list or numpy array, is now a {0}'\
        .format(type(new_row_data))
        raise AssertionError(msg)

    try:
        assert N_elements_new_row == len(new_row_indices), \
                'new_row_data and new_row_indices must have the same size'
    except TypeError:
        msg = 'Argument new_row_indices shall be a list or numpy array, is now a {0}'\
        .format(type(new_row_indices))
        raise AssertionError(msg)

    idx_start_row = A.indptr[row_idx]
    idx_end_row = A.indptr[row_idx + 1]

    A.data = np.r_[A.data[:idx_start_row], new_row_data, A.data[idx_end_row:]]
    A.indices = np.r_[A.indices[:idx_start_row], new_row_indices, A.indices[idx_end_row:]]
    A.indptr = np.r_[A.indptr[:row_idx + 1], A.indptr[(row_idx + 1):] + N_elements_new_row]