getting unique values from a list of dict

Question

Possible Duplicate:
how to uniqify a list of dict in python

I have a list as follows

[
{'x':'1','y':'1'},{'x':'2','y':'2'},{'x':'1','y':'1'}
]

I want to get a new list as follows (unique elements)

[
{'x':'1','y':'1'},{'x':'2','y':'2'}
]

What's the best way?

Are the two identical dicts in the example different objects (i.e., two objects with distinct ids)? If so, the problem is more complex, since methods of making a unique list such as casting to a set, etc. will not work. — Andrew Gorcester, Jul 31 '12 at 14:02

score 5 · Accepted Answer · answered Jul 31 '12 at 14:05

5

import ast

l = [
{'x':'1','y':'1'},{'x':'2','y':'2'},{'x':'1','y':'1'}
]

[ast.literal_eval(el1) for el1 in set([str(el2) for el2 in l])]

Usually an easy solution for keeping unique elements is to add them to a set. However, since a dict is unhashable (can't be put in a set), I provided a workaround. First, the dicts are converted to strings, placed in a set (to keep the unique ones), and then converted back to dicts using ast.literal_eval.

answered Jul 31 '12 at 14:05

Lanaru

9,421
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Why not use a dict of repr(dict) -> dict? – Martijn Pieters Jul 31 '12 at 14:07
Or, do what black_dragon did, cast to tuples then back.. – Martijn Pieters Jul 31 '12 at 14:10
Does `str(d)` always iterate over the key, value pairs in the same order? – DSM Jul 31 '12 at 14:18

score 4 · Answer 2 · answered Jul 31 '12 at 14:08

4

>>> lst = [{'x':'1','y':'1'},{'x':'2','y':'2'},{'x':'1','y':'1'}]
>>> map(dict, set(tuple(x.items()) for x in lst))
[{'y': '1', 'x': '1'}, {'y': '2', 'x': '2'}]
>>>

answered Jul 31 '12 at 14:08

applicative_functor

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1

I'm actually not sure this works. I don't know if it's guaranteed that two equal dicts have their `.items()` return in the same order. – DSM Jul 31 '12 at 14:15
This will not work in Python3. – NightFury13 Aug 23 '20 at 09:52

getting unique values from a list of dict

2 Answers2