Merge lists

OSCC · Python, List · Nov 2, 2020

Merges two or more lists into a list of lists, combining elements from each of the input lists based on their positions.

  • Use max() combined with a list comprehension to get the length of the longest list in the arguments.
  • Use range() in combination with the max_length variable to loop as many times as there are elements in the longest list.
  • If a list is shorter than max_length, use fill_value for the remaining items (defaults to None).
  • zip() and itertools.zip_longest() provide similar functionality to this snippet.
def merge(*args, fill_value = None):
  max_length = max([len(lst) for lst in args])
  result = []
  for i in range(max_length):
      args[k][i] if i < len(args[k]) else fill_value for k in range(len(args))
  return result
merge(['a', 'b'], [1, 2], [True, False]) # [['a', 1, True], ['b', 2, False]]
merge(['a'], [1, 2], [True, False]) # [['a', 1, True], [None, 2, False]]
merge(['a'], [1, 2], [True, False], fill_value = '_')
# [['a', 1, True], ['_', 2, False]]

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