[Tutor] Sorting a dictionary by a value when the values are tuples

[Steven D'Aprano]

ranjan das wrote:
> This is a small example i created
> 
> 
> from operator import itemgetter
> temp={'4':(2,3), '2':(5,8)}
> print temp.items()
> new_temp=sorted(temp.items(), key=itemgetter(1)
> print new_temp

Another syntax error. Please ensure that you test your code before 
posting. In this case, it's easy to fix: you're missing a closing 
bracket in the call to sorted().

> I want to sort the dictionary by the value in the first element of the tuple
> ((2,3) and (5,8)) and then the second value.

That would be the ordinary sort order of tuples.

> How do i do it? by setting key=itemgetter(1), it seems to sort the dict by
> the first value of the tuple. But I am not able to do it for the second
> value.

You can't sort *dicts*, because they are unordered. However, you extract 
the key:value items from the dict into a list, which gives you a list of 
tuples:

 >>> from operator import itemgetter
 >>> temp={'4':(2,3), '2':(5,8)}
 >>> print temp.items()
[('2', (5, 8)), ('4', (2, 3))]

You want to ignore the key part (the first item in the *outer* tuples, 
namely '2' and '4'), and just sort by the value part (the second item of 
the outer tuples, namely (2, 3) and (5, 8) -- note that these are 
themselves also tuples.

The way to sort them is using itemgetter(1), exactly as you tried:

 >>> new_temp=sorted(temp.items(), key=itemgetter(1))
 >>> print new_temp
[('4', (2, 3)), ('2', (5, 8))]

What makes you think that it did not work correctly? Here is a better 
example, showing that it works fine:

 >>> temp = {'a':(2,3), 'b':(5,8), 'c':(5,1), 'd':(2,1)}
 >>> temp.items()
[('a', (2, 3)), ('c', (5, 1)), ('b', (5, 8)), ('d', (2, 1))]
 >>> sorted(temp.items(), key=itemgetter(1))
[('d', (2, 1)), ('a', (2, 3)), ('c', (5, 1)), ('b', (5, 8))]




-- 
Steven