python: sort a nested dictionary

Question

I have a nested dictionary of type following

{id_1 : [ {id_2:score},{id_3:score_2} .... and so on],id_2 :[{id_1:Score_!....]}

so basically a nested dictionary Now I want to sort this dictionary per primary id on the basis of score so basically

{id_1: [{element with max_score},{element_with next max_score....}]... id_2:[{element_with max_score},{element_with next maxx score}...]

also, the function should take an argument say (n) which returns the top n matches or if the n< number of elements of that id then it returns teh complete list any Ideas/ thoughts.. Thanks

You probably have a spurious bracket in the first code snippet -- could you please review this? — Sven Marnach
– Sven Marnach, Commented Nov 21, 2011 at 19:10
Why are the values of the inner list dictionaries, and not just tuples? — Sven Marnach
– Sven Marnach, Commented Nov 21, 2011 at 19:10
@SvenMarnach yepp yepp . Thanks for pointing that out.. basically its a nested dictionary — frazman
– frazman, Commented Nov 21, 2011 at 19:11

Sven Marnach · Accepted Answer · 2011-11-21 19:48:15Z

3

You can use the key parameter to list.sort(). Assuming the outer dictionary is called d, the code could look like this:

for scores in d.itervalues():
    scores.sort(key=lambda x: next(x.itervalues()), reverse=True)

The lambda function simply extracts the single value of the dictionary.

I think you'd be better off using tuples instead of dictionaries as the values of your list:

{id_1: [(id_2, score_2), (id_3, score_3),...], id_2: [(id_1, score_1),...]}

Using this data structure, the sorting code would be

for scores in d.itervalues():
    scores.sort(key=lambda x: x[1], reverse=True)

or equivalently, but slightly faster

for scores in d.itervalues():
    scores.sort(key=operator.itemgetter(1), reverse=True)

edited Nov 21, 2011 at 19:48

answered Nov 21, 2011 at 19:12

Sven Marnach

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4 Comments

Andrew Clark Over a year ago

Should that be scores.sort(...)?

frazman Over a year ago

So is d the list.. or a nesteddict??

Andrew Clark Over a year ago

+1, might need reverse=True as well since the OP wants higher scores first.

Sven Marnach Over a year ago

@Jerod I don't understand. This answer contains three possible solutions, and the first one is based on the exact data structure the OP provided. How does this not answer the original question?

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