lambda iteration over list

Question

can somebody help me with a code error.

What I need is to multiply 2nd and 3rd element of each list and then sum up four values (total result=431900) I've done it with a simple for loop:

lst = [['switch', '4', '12500'], ['hub', '1', '500'], ['router', '1', '1400'], ['jacks', '40', '9500']]

summ = 0
for i in lst:
    summ += int(i[1])*int(i[2])
print(summ)

But I wanted to improve it with a function or lambda:

from functools import reduce

result = reduce(lambda x, y: int(x[1])*int(x[2]))+(int(y[1])*int(y[2]), lst)
print(result)

It returns only first iteration (50500), on second x becomes None (y becomes the next list) and the program returns an error: TypeError: 'NoneType' object is not subscriptable.

I don't get why x becomes None, what is wrong here?

Why are you using reduce and not sum ?

Jon Clements
– Jon Clements

2022-04-24 11:11:30 +00:00
Commented Apr 24, 2022 at 11:11 — Jon Clements
– Jon Clements, Commented Apr 24, 2022 at 11:11

Onyambu · Accepted Answer · 2022-04-24 11:36:50Z

1

Note that once you have summed, x is now a double and not a list thus not subscriptable. You thus need to make use of the initial (ie 3rd) parameter. Ans since its a sum, we start summing from 0.

reduce(lambda x, y: x + int(y[1]) * int(y[2]), lst, 0)
Out[230]: 431900

answered Apr 24, 2022 at 11:36

Onyambu

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