itertool group dynamic element in list python

Question

I have a list of lists with multi columns:

column = [id, date,col1, col2...coln]
list_OfRows = [[1,date1, 10,20 ...23],
              [1,date1, 1,10 ...33],
              [2,date2, 3,7...8],
              [2,date2, 21,9...23],
              [2,date3, 10,56 ...20],
              [2,date4, 10,20 ...42]]

I want to group by on id and date and do sum on cols WITHOUT USING PANDAS

RESULT = [[1,date1, 11,30 ...56],
         [2,date2, 24,16...31],
         [2,date3, 10,20 ...20],
         [2,date4, 10,20 ...42]]

Please always provide a minimal reproducible example and be sure to read stackoverflow.com/help/how-to-ask — Pitto
– Pitto, Commented May 31, 2021 at 11:40
What about mapReduce or simply use a dictionary where you collect the records by id and then apply the aggregation function. — samusa
– samusa, Commented May 31, 2021 at 11:46

Ma0 · Accepted Answer · 2021-05-31 12:01:13Z

3

You can do it like this:

from itertools import groupby


list_OfRows.sort(key=lambda x: x[:2])
res = []
for k, g in groupby(list_OfRows, key=lambda x: x[:2]):
    res.append(k + list(map(sum, zip(*[c[2:] for c in g]))))

which produces:

[[1, 'date1', 11, 30, 56], 
 [2, 'date2', 24, 16, 31], 
 [2, 'date3', 10, 56, 20], 
 [2, 'date4', 10, 20, 42]]

edited May 31, 2021 at 12:01

answered May 31, 2021 at 11:52

Ma0

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3 Comments

Daniel Hao Over a year ago

Perfect usage of groupby. Very elegant solution.

stanislass Over a year ago

@Ma0 thanks ! i this error :

res.append((k + list(map(sum, zip(*[c[2:] for c in g]))))) ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

some advice?

Ma0 Over a year ago

are these numpy arrrays?

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