delete items from list by indices

Peter Otten __peter__ at web.de
Wed Sep 23 10:48:27 CEST 2009


blumenkraft wrote:

> I have some list:
> x = [8, 9, 1, 7]
> and list of indices I want to delete from x:
> indices_to_delete = [0, 3], so after deletion x must be equal to [9,
> 1].
> 
> What is the fastest way to do this? Is there any builtin?

Why's that obsession with speed?

>>> items = ["a", "b", "c", "d"]
>>> delenda = [0, 3]
>>> for i in sorted(delenda, reverse=True):
...     del items[i]
...
>>> items
['b', 'c']


>>> items = ["a", "b", "c", "d"]
>>> delenda = set([0, 3])
>>> items = [item for index, item in enumerate(items) if index not in 
delenda]
>>> items
['b', 'c']

If you really need to modify the list in place change

items = [item for ...]

to

items[:] = [item for ...]

Try these and come back to complain if any of the above slows down your 
script significantly...

Peter




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