CODEWITHSUNDEEP
pythonlistpython-2.7
dylnmc
dylnmc

Reputation: 4010

Removing indexes from a list

I'm facing a somewhat troubling problem: I have a list (for example (2, 5, 7, 3, 8)) and I need to remove a couple of those but not all. Let's say I need to remove indexes 1, 3 and 4 and I want to do that in a loop. Is there anyway (in Python or logically) to remove those indexes easily in a loop.

If I have a list remIndexes = (1, 3, 4), as soon as I remove index 1, everything moves down one, so now I have (2, 7, 3, 8) and the indexes for the numbers I wanted to remove are shifted down by one.

Does python provide a neat way of doing this or am I going to have to order the list remIndexes and then go backwards through the list?

Note: remIndexes should be in order, but it could potentially not be in order. Ordering it isn't very hard, however.

UPDATE:

Why does

lst = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
for ind, num in enumerate(lst):
    print lst.pop(ind)

actually work????? (It prints 2 4 6 8 0 each on a newline.)

Does python freeze a list while you are in a for loop?

Upvotes: 0

Views: 376

Answers (1)

falsetru
falsetru

Reputation: 369054

Iterate the reversed indexes:

>>> lst = [2, 5, 7, 3, 8]
>>> indexes = 1, 3, 4
>>> for i in reversed(indexes):
...     del lst[i]
...
>>> lst
[2, 7]

Or use sorted(indexes, reverse=True) if the indexes is not sorted.

Using list comprehension with enumerate:

>>> lst = [2, 5, 7, 3, 8]
>>> indexes = 1, 3, 4
>>> indexes = set(indexes)  # `x in set` is faster than `x in tuple/list`
>>> [x for i, x in enumerate(lst) if i not in indexes]
[2, 7]

Upvotes: 1

Related Questions