def key_gen(file, ix):
  """ Generate list of keys for file based on index values
  Input arguments:
    file : h5py File object
           Loaded using h5py.File(path : string)
    ix : list[int]
         List of index values to find file keys for.
  """
  keys = list(file.keys())
  split_keys = [key.split('_') for key in keys]
  new_keys = []

  for i, key in enumerate(split_keys):
    if int(key[1]) in ix:
      new_keys.append(keys[i])

  return new_keys