What is the simplest and most efficient function to return a sublist based on an index list?

Question

Say I have a list l:

['a','b','c','d','e']

and a list of indexes idx:

[1,3]

What is the simplest and most efficient function that will return:

['b','d']

Answer 1

Try using this:

[l[i] for i in idx]

Answer 2

You want operator.itemgetter.

In my first example, I'll show how you can use itemgetter to construct a callable which you can use on any indexable object:

from operator import itemgetter
items = itemgetter(1,3)
items(yourlist)  #('b', 'd')

Now I'll show how you can use argument unpacking to store your indices as a list

from operator import itemgetter
a = ['a','b','c','d','e']
idx = [1,3]
items = itemgetter(*idx)
print items(a)  #('b', 'd')

Of course, this gives you a tuple, not a list, but it's trivial to construct a list from a tuple if you really need to.