Turning a list of dictionaries into a list of lists

Question

I know this is possible with list comprehension but I can't seem to figure it out. Currently I have a list of dictionaries like so:

 [ {'field1': 'a', 'field2': 'b'},
   {'field1': 'c', 'field2': 'd'},
   {'field1': 'e', 'field2': 'f'} ]

I'm trying to turn this into:

list = [
    ['b', 'a'],
    ['d', 'c'],
    ['f', 'e'],
]

JuniorCompressor · Accepted Answer · 2015-07-25T13:59:28.843

5

You can try:

[[x['field2'], x['field1']] for x in l]

where l is your input list. The result for your data would be:

[['b', 'a'], ['d', 'c'], ['f', 'e']]

This way you ensure that the value for field2 comes before the value for field1

edited Jul 25 '15 at 13:59

answered Jul 25 '15 at 13:52

JuniorCompressor

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score 4 · Answer 2 · answered Jul 25 '15 at 13:51

Just return the dict.values() lists in Python 2, or convert the dictionary view to a list in Python 3:

[d.values() for d in list_of_dicts]  # Python 2
[list(d.values()) for d in list_of_dicts]  # Python 3

Note that the values are not going to be in any specific order, because dictionaries are not ordered. If you expected them to be in a given order you'd have to add a sorting step.

CrazyCasta · Answer 3 · 2015-07-25T13:52:44.363

0

I'm not sure what ordering you want, but for no order you could do:

list_ = [list(_.values()) for _ in dict_list]

edited Jul 25 '15 at 13:52

answered Jul 25 '15 at 13:51

CrazyCasta

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Note that the `list()` call is only needed for Python 3, in Python 2 `dict.values()` returns a list already. – Martijn Pieters Jul 25 '15 at 13:54
Well, it's not going to break anything so who cares. – CrazyCasta Jul 25 '15 at 13:56
If this is on a critical path you may care. – Martijn Pieters Jul 25 '15 at 13:57
If it's on a critical path then he should figure out how to get the data in the right form in the first place. I guarantee that stepping through the data to generate the list is going to take WAY longer then shallow copying the list. – CrazyCasta Jul 25 '15 at 13:59

user3636636 · Answer 4 · 2015-07-25T14:00:18.737

0

You can use list comprehension

Python 3

>>>listdict = [ {'field1': 'a', 'field2': 'b'},
...             {'field1': 'c', 'field2': 'd'},
...             {'field1': 'e', 'field2': 'f'} ]

>>>[[a for a in dict.values()] for dict in listdict]
[['b', 'a'], ['d', 'c'], ['f', 'e']]

Python 2

>>>[dict.values() for dict in listdict]
[['b', 'a'], ['d', 'c'], ['f', 'e']]

edited Jul 25 '15 at 14:00

answered Jul 25 '15 at 13:53

user3636636

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Turning a list of dictionaries into a list of lists

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