Group dictionary key values in python

Question

I have the following dictionary

mylist = [{'tpdt': '0.00', 'tmst': 45.0, 'tmdt': 45.0, 'pbc': 30, 'remarks': False, 'shift': 1, 'ebct': '0.00', 'tmcdt': '0.00', 'mc_no': 'KA20'}, 
          {'tpdt': '0.00', 'tmst': 45.0, 'tmdt': 45.0, 'pbc': 30, 'remarks': False, 'shift': 1, 'ebct': '0.00', 'tmcdt': '0.00', 'mc_no': 'KA20'}, 
          {'tpdt': '0.00', 'tmst': 55.0, 'tmdt': 55.0, 'pbc': 30, 'remarks': False, 'shift': 1, 'ebct': '0.00', 'tmcdt': '0.00', 'mc_no': 'KA23'}, 
          {'tpdt': '0.00', 'tmst': 55.0, 'tmdt': 55.0, 'pbc': 30, 'remarks': False, 'shift': 1, 'ebct': '0.00', 'tmcdt': '0.00', 'mc_no': 'KA23'}]

I want to get the sum of the key 'tmst' for every dictionary values 'KA20' and 'KA23' in the list of dictionaries.

Could you please have your suggestions on this??

Answer 1

You can use itertools.groupby:

>>> for key, group in itertools.groupby(mylist, lambda item: item["mc_no"]):
...     print key, sum([item["tmst"] for item in group])
... 
KA20 90.0
KA23 110.0

Note that for groupby to work properly, mylist has to be sorted by the grouping key:

from operator import itemgetter

mylist.sort(key=itemgetter("mc_no"))

Answer 2

First you needs to sort that list of dictionaries..using following code.. Ex.

animals = [{'name':'cow', 'size':'large'},{'name':'bird', 'size':'small'},{'name':'fish', 'size':'small'},{'name':'rabbit', 'size':'medium'},{'name':'pony', 'size':'large'},{'name':'squirrel', 'size':'medium'},{'name':'fox', 'size':'medium'}]

import itertools
from operator import itemgetter
sorted_animals = sorted(animals, key=itemgetter('size'))

then you use following code

for key, group in itertools.groupby(sorted_animals, key=lambda x:x['size']):
    print key,
    print list(group)

After you will get following result...

large [{'name': 'cow', 'size': 'large'}, {'name': 'pony', 'size':'large'}]
medium [{'name': 'rabbit', 'size': 'medium'}, {'name': 'squirrel', 'size':'medium'}, {'name': 'fox', 'size': 'medium'}]
small [{'name': 'bird', 'size': 'small'}, {'name': 'fish', 'size': 'small'}]