List comprehension combine 2 elements in nested list

Question

Is it possible to use list comprehension to combine 2 elements in a nested list based on the occurrence of a character, eg: if you encounter '+' combine with the next element? I have some code that does this using nested loops, but trying to achieve using list comprehension.

Input: l = [['A-2', 'A-3', 'A-4', '+', '100', 'A-5'],['B-2', 'B-3', 'B-4', '+', '500', 'B-5']]

Output: l = [['A-2', 'A-3', 'A-4', '+100', 'A-5'],['B-2', 'B-3', 'B-4', '+500', 'B-5']]

Code:

for nested in l: 
   z = iter(nested)
   for i in z:
      if i == '+':
         i = i+next(z)

[SO post](https://stackoverflow.com/questions/18072759/list-comprehension-on-a-nested-list) for nested list comprehension — willwrighteng, Oct 28 '20 at 16:29
@will.cass.wrig but far from duplicate. This is more complex, combining some elements and leaving some as is. — user2390182, Oct 28 '20 at 16:30
@schwobaseggl agreed, just wanted to include it as a reference for other variations on the solution. your solution is good, that's why I upvoted it. — willwrighteng, Oct 28 '20 at 17:15

user2390182 · Answer 1 · 2020-10-28T16:58:10.910

5

The following will work:

[[x + next(i) if x == "+" else x for x in i] for i in map(iter, l)]

# [['A-2', 'A-3', 'A-4', '+100', 'A-5'], ['B-2', 'B-3', 'B-4', '+500', 'B-5']]

If the last element might be a "+", you could pass a default value to next

next(i, "")

to avoid an error.

edited Oct 28 '20 at 16:58

answered Oct 28 '20 at 16:29

user2390182

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The OP probably doesn't need it, but you could do `next(i, '')` in case the last element is an "+". – ekhumoro Oct 28 '20 at 16:55

List comprehension combine 2 elements in nested list

1 Answers1