Using the "i-=smallest" statement in the code below, I intend to alter my original array arr, but that isn't happening. What do I do?

Question

Here's the code:

n = int(input())
arr = input().split()
arr = [int(x) for x in arr]
smallest = 1001
while(True):
    if smallest==0:
        break
    arr.sort()
    count = 0
    smallest = arr[0]
    for i in arr:
        if i==0:
            arr.remove(i)
        i-=smallest           #This statement.
        count+=1
    print(count)

For input: (n=)6 and (arr=)5 4 4 2 2 8 The output I'm getting is: 6 6 6... However, according to me, if my logic works (and the aforementioned statement actually edits my original array elements), the output should turn out to be 6 4 2 1 instead.

I might have got whole of the thing wrong. I'm an amateur. Any sort of help is appreciated.

Give more detail how your logic should work. With the (wrong) code, we can't see your thought. — Jeon, Sep 23 '16 at 18:36

score 2 · Accepted Answer · edited May 23 '17 at 11:48

Let's look at the inside loop

for i in arr:
    if i==0:
        arr.remove(i)
    i-=smallest
    count+=1

It assigns the first value in arr to i. Since no value of the array is zero, it doesn't remove anything from the list.

It then reassigns the value of i by subtracting the smallest value. For the first time through the loop it assigns the value of zero to i. Then it increments count. The list arr is unchanged. The line i=-smallest has no effect since i is reassigned to the next value of the list.

So, with the values 5 4 4 2 8 8 (none of which are zero) that loop is equivalent to

for i in arr:
    count+=1

Which is why it always prints 6. I'm not sure why you think it should print 6 4 2 1. I suspect you think the list is being changed, but that the line if i==0 is always false.

Changing the object being iterated over in a for loop is guaranteed to confuse you. There is almost certainly a better way to achieve what you want. See for example Remove items from a list while iterating

@Jeon I want my array values to change with the "i-=smallest" statement. How do I achieve that? — sbhayana26, Sep 23 '16 at 18:41
In short don't. Build a new list with a comprehension. see the linked answer. — James K, Sep 23 '16 at 18:46
Just looking at that. Thank you! The (linked) answer is a bit hard to comprehend for me (novice level), though. — sbhayana26, Sep 23 '16 at 18:50

Using the "i-=smallest" statement in the code below, I intend to alter my original array arr, but that isn't happening. What do I do?

1 Answers1