Convert a List of Dictionaries into a Dictionary of Tuples

Question

How do I convert a List of Dictionaries that looks something like this:

[{'id':2, 'risk':'a'}, 
 {'id':1, 'risk':'a'}, 
 {'id':32,'risk':'aa'},
 {'id':2, 'risk':'aa'}, 
 {'id':7, 'risk':'a'}, 
 {'id':7, 'risk':'b'}]

into a Dictionary of Tuples that will look like this after sorting:

{1:('a', ), 2:('a','aa'), 7:('a','b'), 32:('aa', )}

Answer 1

You can use a defaultdict to automatically create the tuples, then just iterate over the list_of_dicts :

list_of_dicts = [{'id':2, 'risk':'a'}, 
 {'id':1, 'risk':'a'}, 
 {'id':32,'risk':'aa'},
 {'id':2, 'risk':'aa'}, 
 {'id':7, 'risk':'a'}, 
 {'id':7, 'risk':'b'}]

from collections import defaultdict

dict_of_tuples = defaultdict(tuple)

for dct in list_of_dicts:
    dict_of_tuples[dct['id']] += (dct['risk'],)

Which results in:

>>> dict_of_tuples
defaultdict(<type 'tuple'>, {32: ('aa',), 1: ('a',), 2: ('a', 'aa'), 7: ('a', 'b')})

If you then want a sorted dictionary:

>>> from collections import OrderedDict
>>> OrderedDict(sorted(dict_of_tuples.items()))
OrderedDict([(1, ('a',)), (2, ('a', 'aa')), (7, ('a', 'b')), (32, ('aa',))])

Answer 2

The dict.setdefault method makes short work of this kind of problem:

>>> lod = [{'id':2, 'risk':'a'}, 
           {'id':1, 'risk':'a'}, 
           {'id':32,'risk':'aa'},
           {'id':2, 'risk':'aa'}, 
           {'id':7, 'risk':'a'}, 
           {'id':7, 'risk':'b'}]
>>> dot = {}
>>> for d in lod:
        idnum, risk = d['id'], d['risk']
        dot.setdefault(idnum, []).append(risk)

>>> dot
{32: ['aa'], 1: ['a'], 2: ['a', 'aa'], 7: ['a', 'b']}

You can also use collections.defaultdict to create the same effect, but that doesn't create a regular dictionary and it requires an understanding of factory functions and zero argument constructors.

Answer 3

Generally people forget to use dict.get method in similar situations. So with basic python functions:

list_of_dicts = [{'id':2, 'risk':'a'}, 
    {'id':1, 'risk':'a'}, 
    {'id':32,'risk':'aa'},
    {'id':2, 'risk':'aa'}, 
    {'id':7, 'risk':'a'}, 
    {'id':7, 'risk':'b'}]

final_dict = {}

for item in list_of_dicts:
    final_dict[item['id']] = final_dict.get(item['id'], tuple()) + (item['risk'],)


>> {1: ('a',), 2: ('a', 'aa'), 7: ('a', 'b'), 32: ('aa',)}

Answer 4

Doing it in a longer way. Not as neat as agf's solution, but it works

new_dict = {}
for x in my_dict_list: 
    m = new_dict.get(x['id'],())
    m += (x['risk'],)
    new_dict[x['id']] = m

Input

my_dict_list = [{'id':2, 'risk':'a'}, 
                {'id':1, 'risk':'a'}, 
                {'id':32,'risk':'aa'},
                {'id':2, 'risk':'aa'}, 
                {'id':7, 'risk':'a'}, 
                {'id':7, 'risk':'b'}]

Output

>>> new_dict
{32: ('aa',), 1: ('a',), 2: ('a', 'aa'), 7: ('a', 'b')}