code: def _bulk_length(df, *args):
      return df.groupby("LKRecID")["item"].count()
  
file_path: lkpy/lenskit/topn.py
imports: import logging
  import functools
  import numpy
  import pandas
  from .metrics.topn import *
  from .util import Stopwatch
label_desc: Use image node_id 2 for calling a global function with example usage: _bulk_length(df) and returns: df