CODEWITHSUNDEEP
pythonpython-3.x
Tanay Roman
Tanay Roman

Reputation: 115

How does python max(list) function work?

I have the following code that doesn't work the way it should.

n = int(input())
arr = map(int, input().split())

num=max(arr)
x=list(set(arr))
print (x)

This returns and empty list "[]". However, if I remove the num=max[arr] line from the code, it works as expected.

n = int(input())
arr = map(int, input().split())

x=list(set(arr))
print (x)

And the output is a list of all elements without duplicates. I wanted to use the max() value somewhere else in the program, but it seems to break the list formation. Why does this happen? Is there a basic property of the max function that I'm missing?

Edit: Why are people downvoting this without any answers? I'm fairly new to python and any help would be appreciated. If I made a silly mistake please point that out.

Upvotes: 0

Views: 187

Answers (2)

dfundako
dfundako

Reputation: 8324

I'm not sure why you need to use map in this case. Another thing is that you will throw errors on your input if the user does not provide a single int since you are trying to convert it. You can take your input, like a string of '1 4 6 23 5', convert it to a list of ints, and then find the max. 

n = '1 4 6 23 5'
arr = [int(x) for x in n.split()]
max(arr)

Upvotes: 0

Patrick Artner
Patrick Artner

Reputation: 51653

n = int(input())  # unused - why put it in your example?
arr = map(int, input().split())  # returns an iterator

num=max(arr)      # consumes the iterator
x=list(set(arr))  # nothing in the iterator anymore
print (x)         # prints nothing

Fix:

n = int(input())  # unused - why put it in your example?
arr = set(map(int, input().split()))  # returns an set named arr

num=max(arr)      # get num as max from set 
print (arr)       # prints the set named arr

In python 2 map behaved differently - for 3 its an iterator. Once consumed, iterators are "empty". You can see for yourself if you print(type(arr)) for the result of your map operation.

Read: map()

Upvotes: 3

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