Finding a sum in nested list using a lambda function

Question

I have a data structure similar to this

table = [
    ("marley", "5"),
    ("bob", "99"),
    ("another name", "3")
]

What I would like to do, to get the sum of the 2nd column (5 + 99 + 3) functionally like this:

total = sum(table, lambda tup : int(tup[1]))

That would be similar syntax to the python function sorted, but that's not how you would use python's sum function.

What's the pythonic/functional way to sum up the second column?

score 60 · Accepted Answer · answered Jul 30 '14 at 21:51

60

One approach is to use a generator expression:

total = sum(int(v) for name,v in table)

answered Jul 30 '14 at 21:51

Peter de Rivaz

rth · Answer 2 · 2022-01-13T00:25:29.397

13

reduce can help

from functools import reduce

total = reduce(lambda accumulator,element:accumulator+int(element[1]), table,0)

edited Jan 13 '22 at 00:25

answered Jul 30 '14 at 21:54

rth

1

I expect this is using the `reduce` defined in `functools`. I just added that import. – Steven C. Howell Apr 27 '21 at 14:06
1

Thanks @StevenC.Howell for clarification! In 2014, the answer was in Python2 where reduce is the basic functions. Yes for Python3 `reduce ` must be imported – rth Apr 28 '21 at 15:43
Please properly name your arguments, `x` and `y` are not any helpful. I quickly wanted to know which one is sum and which one is current. Your "answer" isn't any helpful on that. – Luka Samkharadze Jan 11 '22 at 23:09

score 11 · Answer 3 · answered Jul 30 '14 at 21:59

11

If you want to use lambda the following should solve it:

total = sum(map(lambda x: int(x[1]), table))

answered Jul 30 '14 at 21:59

FredrikHedman

Joran Beasley · Answer 4 · 2014-07-30T22:00:43.760

3

sum(map(int,zip(*table)[-1]))

is one way to do it ... there are many options however

edited Jul 30 '14 at 22:00

answered Jul 30 '14 at 21:51

Joran Beasley

1

option1 - ```sum(map(int, map(operator.itemgetter(1), table)))``` – wwii Jul 30 '14 at 22:13

score 2 · Answer 5 · answered Jul 30 '14 at 22:12

2

You can also get at the values in a dictionary:

total = sum(map(int, dict(table).values())

This may be a little obscure.

answered Jul 30 '14 at 22:12

Peter Wood

2

This answer works, but it creates a dictionary per row in the table. This isn't very memory efficient. – hlin117 Jul 30 '14 at 22:15
1

It creates just one dictionary using the table, and iterates over the values converting each one to an integer, and then sums them. For a big table it could be prohibitive. @PeterdeRivaz's answer using a generator is the most Pythonic. – Peter Wood Jul 31 '14 at 09:42

score 0 · Answer 6 · edited Nov 05 '19 at 05:07

0

One way is using indexing.

total=sum(items[1] for items in table)

edited Nov 05 '19 at 05:07

4b0

answered Nov 05 '19 at 05:03

SRG

6 Answers6