def _codes_to_ints(self, codes):
<EOL>codes <<= self.offsets<EOL>if codes.ndim == <NUM_LIT:1>:<EOL><INDENT>return np.bitwise_or.reduce(codes)<EOL><DEDENT>return np.bitwise_or.reduce(codes, axis=<NUM_LIT:1>)<EOL>
Transform combination(s) of uint64 in one uint64 (each), in a strictly
monotonic way (i.e. respecting the lexicographic order of integer
combinations): see BaseMultiIndexCodesEngine documentation.

Parameters
----------
codes : 1- or 2-dimensional array of dtype uint64
    Combinations of integers (one per row)

Returns
------
int_keys : scalar or 1-dimensional array, of dtype uint64
    Integer(s) representing one combination (each).