Group List Of Tuples By Item

I have this list as example: [(148, Decimal('3.0')), (325, Decimal('3.0')), (148, Decimal('2.0')), (183, Decimal('1.0')), (308, Decimal('1.0')), (530, Decimal('1.0')), (594, Decima

Solution 1:

You would first need to sort the data for the groupby to work, it groups consecutive elements based on the key you provide:

import operator, itertools
fromdecimal import *
test=[(148, Decimal('3.0')), (325, Decimal('3.0')), (148, Decimal('2.0')), (183, Decimal('1.0')), (308, Decimal('1.0')), (530, Decimal('1.0')), (594, Decimal('1.0')), (686, Decimal('1.0')), (756, Decimal('1.0')), (806, Decimal('1.0'))]

for _k, data in itertools.groupby(sorted(test), operator.itemgetter(0)):
    print list(data)

But you would be better using a dict to group to avoid an unnecessary O(n log n) sort:

from collections import defaultdict

d = defaultdict(list)

for t in test:
    d[t[0]].append(t)

for v in d.values():
    print(v)

Both would give you the same groupings, just not necessarily in the same order.

Solution 2:

itertools.groupby() requires the data to be consistent or sorted.

[(148, Decimal('3.0')), (148, Decimal('2.0')), (325, Decimal('3.0'))] will work but [(148, Decimal('3.0')), (325, Decimal('3.0')), (148, Decimal('2.0'))] will not as the id is 148, 325, 148 instead of 148, 148, 325.