Getting errors when computing the length of list of lists

Question

I have a list of lists. I am trying to find the indices of lists whose length is 4. Here is the code:

for i, j in enumerate(list_of_lists):
  if [x for x in list_of_lists if len(x) == 4] in j:
    print(i)

Alongside the correct indices, I also get the index of a list whose length is 1. Is there something wrong in my code? I have no idea why this happens.

You overcomplicated things and then everything went wrong. Why not a simple if len(j) == 4:? — Matthias
– Matthias, Commented Jun 16, 2022 at 14:11

Timur Shtatland · Accepted Answer · 2022-06-16 14:17:27Z

4

When you iterate over list_of_lists like so, j is the inner list, so you need to check whether len(j) == 4:

list_of_lists = [[0, 1, 2, 3], [], [0], [0, 1, 2, 3],]

for i, j in enumerate(list_of_lists):
    if len(j) == 4:
        print(i)
# 0
# 3

edited Jun 16, 2022 at 14:17

answered Jun 16, 2022 at 14:11

Timur Shtatland

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1 Comment

Nanda Over a year ago

Thank you! Let me please accept nonDucor's answer instead of yours simply because it is more general.

nonDucor · Accepted Answer · 2022-06-16 14:13:48Z

2

If you prefer to collect the indices instead of printing them, it is even simpler:

indices = [i for i, j in enumerate(list_of_lists) if len(j) == 4]

answered Jun 16, 2022 at 14:13

nonDucor

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Comments

Darren · Accepted Answer · 2022-06-16 14:32:02Z

0

    for i, j in enumerate(list_of_lists):
        if len(j) == 4:
            print(i)

Can you try this code? Actually, i is the index, and j is the value.

answered Jun 16, 2022 at 14:32

Darren

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1 Comment

Community Over a year ago

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