Get the item that maximizes a function together with the maximized value from a python list

Question

As the code below, I know how to get the item that maximize a function from a list, but I also want to get the maximized value together with the item. In reality I have a very computationally expensive function so I don't want to run the function again. Here I just use a sigmoid function as an example.

import math

lst = list(range(100))
maxnum = max(lst, key=lambda x: 1 / (1 + math.exp(-x)))
maxval = 1 / (1 + math.exp(-maxnum))
print(maxnum, maxval)

score 1 · Accepted Answer · answered Nov 14 '20 at 10:10

1

Use a tuple to store both maxnum and maxval, as follows, then pass as key the value in the second position (using itemgetter in the code below):

import math
from operator import itemgetter

lst = list(range(100))


def sigmoid(x):
    return 1 / (1 + math.exp(-x))

result = max((e, sigmoid(e))  for e in lst, key=itemgetter(1))


print(result)

Output

(37, 1.0)

answered Nov 14 '20 at 10:10

Dani Mesejo

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This is great answer. Just curious, is it possible to still use a lambda expression? – Shaun Han Nov 14 '20 at 10:18
Where do you want to use the lambda expression? You can change itemgetter by a lambda expression, but not sure what you mean – Dani Mesejo Nov 14 '20 at 10:24
I get the error "Generator expression must be parenthesized if not sole argument". – Shaun Han Nov 14 '20 at 10:45
1

```result = max(((e, sigmoid(e)) for e in lst), key=itemgetter(1))``` works for me – Shaun Han Nov 14 '20 at 10:45

Get the item that maximizes a function together with the maximized value from a python list

1 Answers1