Find the maximum absolute value in a list

Question

I'm looking to get the maximum absolute value in a random list. I need to create it in a function. I'm not sure what I'm doing wrong here. I have a for loop setup so it should check each number but it's only returning the first value.

def main():
    print(maxabsinlst([-19, -3, 20, -1, 5, -25]))

def maxabsinlst(num):
    for x in (num):
        max_abs_value = num[5]
        if abs(x) > max_abs_value:
            max_abs_value = abs(x)
            return max(abs(max_abs_value))

main()

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score 4 · Answer 1 · answered Jul 31 '20 at 01:28

4

The shortest way would be:

def maxabsinlst(num):
    return max(map(abs, num))

The map() function applies abs() to each number on the list, and returns a list of these absolute values, then max() finds the maximum in the list.

answered Jul 31 '20 at 01:28

Ken Y-N

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You're still using Python 2? – superb rain Jul 31 '20 at 01:31
1

Not sure what you're getting at. I'm using Python 3 here. – Ken Y-N Jul 31 '20 at 01:32
In Python 3 it's not a list. – superb rain Jul 31 '20 at 01:33
@superbrain What are you talking about? This is python3? – Jacques Jul 31 '20 at 01:35
In Python 3, `map` doesn't return a list. – superb rain Jul 31 '20 at 01:36
Does it matter? It gets immediately passed into `max`. – Daniel Walker Jul 31 '20 at 01:57
@DanielWalker I'd say if it didn't matter, they wouldn't have changed it :-) – superb rain Jul 31 '20 at 02:01
@DanielWalker Or if you meant whether it mattered here... well, I'd say it matters to not misinform readers. – superb rain Jul 31 '20 at 10:07
Ah, I understand. – Daniel Walker Jul 31 '20 at 15:20

bigbounty · Answer 2 · 2020-07-31T01:30:31.943

You are assigning max_abs_value to num[5] inside the loop. Instead assign it as first element of list then loop through it comparing with other elements

def main():
    print(maxabsinlst([-19, -3, 20, -1, 5, -25]))

def maxabsinlst(num):
    max_abs_value = abs(num[0])
    for x in num[1:]:
        if abs(x) > max_abs_value:
            max_abs_value = abs(x)
    return max_abs_value

main()

OR

In [36]: max(abs(i) for i in [-19, -3, 20, -1, 5, -25])
Out[36]: 25

hrokr · Answer 3 · 2020-08-07T06:53:08.173

2

You can make this quite a bit more concise:

def max_abs_in_lst(num):
    num = [abs(i) for i in num]
    return max(num)

edited Aug 07 '20 at 06:53

answered Jul 31 '20 at 01:32

hrokr

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score 1 · Answer 4 · answered Jul 31 '20 at 01:28

1

max_abs_value = num[5]

Every time the for loop runs, it is setting the max value to -25. Store the value outside the for loop and initialize it with max_abs_value = 0

answered Jul 31 '20 at 01:28

RyanJMcGowan

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score 1 · Answer 5 · answered Jul 31 '20 at 01:29

There are a few issues with your function. First, you're setting max_abs_value at every iteration of the for loop. Second, you're assuming that the list passed to the function will have length 6 every time. Third, you never computed the absolute value of num[5]. So, you're comparing abs(x) to a negative number. Fourth, you're returning from the function as soon as you find any value greater than max_abs_value. You have no guarantee that it was the the greatest value in the list.

What you want is

def maxabsinlist(num):
    max_abs_value=abs(num[0])
    for x in num[1:]:
        value=abs(x)
        if value > max_abs_value:
            max_abs_value=value
    return max_abs_value

Find the maximum absolute value in a list

5 Answers5