docstr: Inverse operation to `split`, with indices=None 
docstr_tok: ["Inverse","operation","to","`","split","`",",","with","indices=None"]
code: def unsplit(self, extra_shape, inputs, segment_ids):
      """Inverse operation to `split`, with indices=None"""
      output = np.zeros((len(segment_ids),) + extra_shape)
      if len(segment_ids) == 0:
          return output
      K = max(segment_ids) + 1
      counts = np.zeros(K, dtype=int)
      for i, seg_id in enumerate(segment_ids):
          output[i] = inputs[seg_id][counts[seg_id]]
          counts[seg_id] += 1
      return output
  
imports: from functools import partial
  from hypothesis import given, settings
  import numpy
  import unittest
  import hypothesis.strategies
  from caffe2.python import core, workspace
  import caffe2.python.hypothesis_test_util
  import caffe2.python.serialized_test.serialized_test_util
label_desc: Use image node_id 2 for calling the SegmentsTester obj's underlying member method code with example usage: obj.unsplit(extra_shape, inputs, segment_ids) and returns: output, output