Python list group and sum with more fields

Question

I have a list with two integer fields which I would like to sum (string,integer, integer)

myList= [[[\"26-07-2017\",2,0], [\"26-07-2017\",3,0], [\"27-07-2017\",         


        

Answer 1

You can use itertools.groupby to group the items on the date, then use reduce to sum numbers in each group:

from itertools import groupby

lst = [[k] + reduce(lambda x, y: [y[1]+x[1], y[2]+x[2]], g) 
                          for k, g in groupby(myList[0], lambda x: x[0])]
print [lst]
# [[['26-07-2017', 5, 0], ['27-07-2017', 1, 1]]]

_{Python 3 requires importing reduce: from functools import reduce}

---

You could avoid using the relatively less intuitve reduce (also in submission to GvR) by taking the sums in a for loop:

from itertools import groupby

lst = []
for k, g in groupby(myList[0], lambda x: x[0]):
   g =  [sum(d) for d in zip(*(t[1:] for t in g))]
   lst.append([k] + g)
print [lst]
# [[['26-07-2017', 5, 0], ['27-07-2017', 1, 1]]]