code: def compute_number_heads_per_tail_relation_tuples(
      triples: np.ndarray,
  ) -> Mapping[str, int]:
      """Compute number of heads per relation-tail pairs."""
      return _count_two_columns(triples, slice(1, 2), slice(2, 3))
  
imports: from collections import Counter
  from typing import Mapping
  import numpy
label_desc: Use image node_id 2 for calling a global function with example usage: compute_number_heads_per_tail_relation_tuples(triples) and returns: _count_two_columns