Python - Group By And Sum A List Of Tuples

Given the following list: [ ('A', '', Decimal('4.0000000000'), 1330, datetime.datetime(2012, 6, 8, 0, 0)), ('B', '', Decimal('31.0000000000'), 1330, datetime.datetime(2012,

Solution 1:

You want itertools.groupby.

Note that groupby expects the input to be sorted, so you may need to do that before hand:

keyfunc = lambda t: (t[0], t[1], t[3], t[4])
data.sort(key=keyfunc)
for key, rows in itertools.groupby(data, keyfunc):
    print key, sum(r[2] for r in rows)

Solution 2:

>>> [(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)

Solution 3:

If you find yourself doing this a lot with large datasets, you might want to look at the pandas library, which has lots of nice facilities for doing this kind of thing.