python – get list of tuples first index?
Question:
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]
Answers:
>>> 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]
use zip if you need both
>>> r=(1,'one'),(2,'two'),(3,'three')
>>> zip(*r)
[(1, 2, 3), ('one', 'two', 'three')]
You can try this too..
dict(my_list).keys()
Try this.
>>> list(map(lambda x: x[0], my_list))
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]
>>> 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]
use zip if you need both
>>> r=(1,'one'),(2,'two'),(3,'three')
>>> zip(*r)
[(1, 2, 3), ('one', 'two', 'three')]
You can try this too..
dict(my_list).keys()
Try this.
>>> list(map(lambda x: x[0], my_list))