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?

Solution 1

One approach is to use a generator expression:

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

Solution 2

reduce can help

from functools import reduce

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

Solution 3

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

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

Solution 4

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

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

Solution 5

You can also get at the values in a dictionary:

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

This may be a little obscure.

View more solutions

Comments

[wwii]

option1 - sum(map(int, map(operator.itemgetter(1), table)))

[hlin117]

This answer works, but it creates a dictionary per row in the table. This isn't very memory efficient.

[Peter Wood]

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.

[Steven C. Howell]

I expect this is using the reduce defined in functools. I just added that import.

[rth]

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

[Luka Samkharadze]

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.