def __csr_row_indices(indptr):
    # get row index for each M.data element. Hold on, thet'd be da fun!
    return [j for i in range(len(indptr)-1) for j in [i,]*(indptr[i+1] - indptr[i])]
Takes csr_matrix.indptr and returns row indexes for data elements
dataset/ETHPy150Open ksavenkov/recsys-001/recsys/score.py/__csr_row_indices