How to sort multidimensional array by column?

Is there a way to use the sort() method or any other method to sort a list by column? Lets say I have the list:

[
[John,2],
[Jim,9],
[Jason,1]
]

And I wanted to sort it so that it would look like this:

[
[Jason,1],
[John,2],
[Jim,9],
]

What would be the best approach to do this?

Edit:

Right now I am running into an index out of range error. I have a 2 dimensional array that is lets say 1000 rows b 3 columns. I want to sort it based on the third column. Is this the right code for that?

sorted_list = sorted(list_not_sorted, key=lambda x:x[2])

Solution 1:

Yes. The sorted built-in accepts a key argument:

sorted(li,key=lambda x: x[1])
Out[31]: [['Jason', 1], ['John', 2], ['Jim', 9]]

note that sorted returns a new list. If you want to sort in-place, use the .sort method of your list (which also, conveniently, accepts a key argument).

or alternatively,

from operator import itemgetter
sorted(li,key=itemgetter(1))
Out[33]: [['Jason', 1], ['John', 2], ['Jim', 9]]

Read more on the python wiki.

Solution 2:

You can use the sorted method with a key.

sorted(a, key=lambda x : x[1])

Solution 3:

You can use list.sort with its optional key parameter and a lambda expression:

>>> lst = [
...     ['John',2],
...     ['Jim',9],
...     ['Jason',1]
... ]
>>> lst.sort(key=lambda x:x[1])
>>> lst
[['Jason', 1], ['John', 2], ['Jim', 9]]
>>>

This will sort the list in-place.

Note that for large lists, it will be faster to use operator.itemgetter instead of a lambda:

>>> from operator import itemgetter
>>> lst = [
...     ['John',2],
...     ['Jim',9],
...     ['Jason',1]
... ]
>>> lst.sort(key=itemgetter(1))
>>> lst
[['Jason', 1], ['John', 2], ['Jim', 9]]
>>>