Python - Group by and sum a list of tuples

group-by, list-comprehension, python

Solution

>>> [(x[0:2] + (sum(z[2] for z in y),) + x[2:5]) for (x, y) in
      itertools.groupby(sorted(L, key=operator.itemgetter(0, 1, 3, 4)),
      key=operator.itemgetter(0, 1, 3, 4))]
[
  ('A', '', Decimal('21.0000000000'), 1330, datetime.datetime(2012, 5, 14, 0, 0)),
  ('A', '', Decimal('4.0000000000'), 1330, datetime.datetime(2012, 6, 8, 0, 0)),
  ('AA', 'C', Decimal('31.0000000000'), 1330, datetime.datetime(2012, 5, 31, 0, 0)),
  ('B', '', Decimal('7.0000000000'), 1330, datetime.datetime(2012, 5, 24, 0, 0)),
  ('B', '', Decimal('31.0000000000'), 1330, datetime.datetime(2012, 6, 4, 0, 0))
]

(NOTE: output reformatted)

Problem

Given the following list: ``` [ ('A', '', Decimal('4.0000000000'), 1330, datetime.datetime(2012, 6, 8, 0, 0)), ('B', '', Decimal('31.0000000000'), 1330, datetime.datetime(2012, 6, 4, 0, 0)), ('AA', 'C', Decimal('31.0000000000'), 1330, datetime.datetime(2012, 5, 31, 0, 0)), ('B', '', Decimal('7.0000000000'), 1330, datetime.datetime(2012, 5, 24, 0, 0)), ('A', '', Decimal('21.0000000000'), 1330, datetime.datetime(2012, 5, 14, 0, 0)) ] ``` I would like to group these by the first, second, fourth and fifth columns in the tuple and sum the 3rd. For this example I'll name the columns as col1, col2, col3, col4, col5. In SQL I would do something like this: ``` select col1, col2, sum(col3), col4, col5 from my table group by col1, col2, col4, col5 ``` Is there a "cool" way to do this or is it all a manual loop?

Original source