python – get list of tuples first index?

Each Answer to this Q is separated by one/two green lines.

What’s the most compact way to return the following:

Given a list of tuples, return a list consisting of the tuples first (or second, doesn’t matter) elements.

For:

[(1,'one'),(2,'two'),(3,'three')]

returned list would be

[1,2,3]

use zip if you need both

>>> r=(1,'one'),(2,'two'),(3,'three')
>>> zip(*r)
[(1, 2, 3), ('one', 'two', 'three')]

>>> tl = [(1,'one'),(2,'two'),(3,'three')]
>>> [item[0] for item in tl]
[1, 2, 3]

>>> mylist = [(1,'one'),(2,'two'),(3,'three')]
>>> [j for i,j in mylist]
['one', 'two', 'three']
>>> [i for i,j in mylist]
[1, 2, 3]

This is using a list comprehension (have a look at this link). So it iterates through the elements in mylist, setting i and j to the two elements in the tuple, in turn. It is effectively equivalent to:

>>> newlist = []
>>> for i, j in mylist:
...     newlist.append(i)
... 
>>> newlist
[1, 2, 3]

Try this.

>>> list(map(lambda x: x[0], my_list))

You can try this too..

dict(my_list).keys()


The answers/resolutions are collected from stackoverflow, are licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0 .