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

The solution using itertools.groupby and operator.itemgetter functions:

import itertools, operator

l = [['Vienna','2012', 890,503,70],['London','2014', 5400, 879,78],
 ['London','2014',4800,70,90],['Bern','2013',300,450,678],
 ['Vienna','2013', 700,850,90], ['Bern','2013',500,700,90]]

getter = operator.itemgetter(0, 1)  # the sequence to be grouped(first two items)
summed = [[k[0],k[1],sum(sum(d[2:]) for d in list(group))]
          for k, group in itertools.groupby(sorted(l, key=getter), getter)]

print(summed)

The output:

[['Bern', '2013', 2718], ['London', '2014', 11317], ['Vienna', '2012', 1463], ['Vienna', '2013', 1640]]