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snippets/python/s/merge.md

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+---
+title: Merge lists
+type: snippet
+language: python
+tags: [list]
+cover: succulent-2
+dateModified: 2020-11-02T19:28:27+02:00
+---
+
+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()`](https://docs.python.org/3/library/functions.html#zip) and [`itertools.zip_longest()`](https://docs.python.org/3/library/itertools.html#itertools.zip_longest) provide similar functionality to this snippet.
+
+```py
+def merge(*args, fill_value = None):
+  max_length = max([len(lst) for lst in args])
+  result = []
+  for i in range(max_length):
+    result.append([
+      args[k][i] if i < len(args[k]) else fill_value for k in range(len(args))
+    ])
+  return result
+```
+
+```py
+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]]
+```