Get indices of nonzero entries of a csr_matrix

csr_matrix_indices.md

IPython notebook

csr_matrix_indices.py

import scipy.sparse


def csr_matrix_indices(S):
    """
    Return a list of the indices of nonzero entries of a csr_matrix S
    """
    major_dim, minor_dim = S.shape
    minor_indices = S.indices

    major_indices = np.empty(len(minor_indices), dtype=S.indices.dtype)
    scipy.sparse._sparsetools.expandptr(major_dim, S.indptr, major_indices)

    return zip(major_indices, minor_indices)

csr_matrix_indices_demo01.ipynb

csr_matrix_indices_gen.py

def csr_matrix_indices_gen(S):
    """
    Generate the indices of nonzero entries of a csr_matrix S
    """
    major_dim, minor_dim = S.shape
    minor_indices = S.indices

    for i in range(major_dim):
        for j in range(S.indptr[i], S.indptr[i+1]):
            major_index, minor_index = i, minor_indices[j]
            yield major_index, minor_index