Sum nested lists based on condition in Python

Question

I have a nested list looking like this:

[[\'Vienna\',\'2012\', 890,503,70],[\'London\',\'2014\', 5400, 879,78],
 [\'London\',\'2014\',4800,70,90],[\'Bern\',\'201         


        

Answer 1

One way is to split the list of lists into a dict by the key you want (the city and year). Also the defaultdict helps squashing all distances into a flat list

>>> from collections import defaultdict
>>> dct = defaultdict(list)
>>> for item in lst:
...    dct[(item[0], item[1])].extend(item[2:])

Now dct has the integers grouped by the city and year:

>>> dct
defaultdict(, {('Vienna', '2013'): [700, 850, 90], ('London', '2014'): [5400, 879, 78, 4800, 70, 90], ('Vienna', '2012'): [890, 503, 70], ('Bern', '2013'): [300, 450, 678, 500, 700, 90]})

And you can just sum them:

>>> for key in dct:
...    print(key, sum(dct[key]))
... 
(('Vienna', '2013'), 1640)
(('London', '2014'), 11317)
(('Vienna', '2012'), 1463)
(('Bern', '2013'), 2718)