Python Forum
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Removing element from list
#1
Hello guys,

I'm new on the forum. The reason I'm here is that I do not know how to fix my problem and hopefully you can help me.
I want to delete the maximum element from the list with the command "remove". I know that remove, removes the first element that I choose to remove, so I made a loop so if there are two or more maximum elements, all of them should be removed.
It doesn't work. It seems like the loop doesn't go through all elements.

def list(a):
    c=max(a)
    a.remove(c)

    for i in a:
        print(i)
        if i == c:
            a.remove(i)


    if a[len(a)-1] == c:
        a.pop(len(a)-1)

    return a



print(list([1,2,3,4,5,6,6,6,6,6,6,6,6,6]))
Superjoe likes this post
Reply
#2
list is already an object in python. It is recommended you use another name for your function.

It is a bad idea to remove objects from an object while you're iterating over it. It will mess with the iteration. You're doing this in lines 5-8.

An alternative is to make a copy without the objects you want removed, or to remove them outside of an iteration.

Remove by copy elements that don't match
a = [item for item in a if item != c]
Remove without iteration
while c in a:
    a.remove(c)
Remove while iterating over a copy
for i in list(a):
    if i == c:
        a.remove(i)
squall likes this post
Reply
#3
You can approach this from another angle: 'remove first occurence of maximum value n-times', where n is number of occurences of maximum value. It's simple but not efficient:

>>> list_ = [1,2,3,4,5,6,6,6,6,6,6,6,6,6]
>>> max_value = max(list_)                 # find maximum value
>>> repetitions = list_.count(max_value)   # find how many times maximum value occurs
>>> for repetition in range(repetitions):  # remove all maximum values
...     list_.remove(max_value)
...
>>> list_
[1, 2, 3, 4, 5]
tester_V and squall like this post
I'm not 'in'-sane. Indeed, I am so far 'out' of sane that you appear a tiny blip on the distant coast of sanity. Bucky Katt, Get Fuzzy

Da Bishop: There's a dead bishop on the landing. I don't know who keeps bringing them in here. ....but society is to blame.
Reply
#4
Thank you guys. I have used option with while - it spoke to me the most.

Anyway I have a question about that:
for i in list(a):
    if i == c:
        a.remove(i)
What does that list(a) there mean? It doesn't work for me.
Reply
#5
You want to use remove(), which has the problem of removing the first instance. The following removes that largest element until there are no longer any matching elements
a = [4,6,8,10,4,7,10,9]
c = max(a)
try :
    while True:
        a.remove(c)
except ValueError:
    pass
print(a)
Output:
[4, 6, 8, 4, 7, 9]
Reply
#6
(Nov-22-2020, 10:16 AM)squall Wrote: Anyway I have a question about that:
for i in list(a):
    if i == c:
        a.remove(i)
What does that list(a) there mean? It doesn't work for me.

It creates a new (different) list from some other object.
l = [1, 2, 3] # a list
a = l         # a is the *same* list
b = list(l)   # b is a *different* list
l.remove(1)   # removes the "1" from l (and from a since it's the same list)

print(l)
print(a)
print(b)
Output:
[2, 3] [2, 3] [1, 2, 3]
It probably doesn't work for you because you've named your function "list", so you've overriden the internal python "list" function.
Reply
#7
Another way to write line 3 above that may be a little more clear is
b=l.copy()
Reply


Possibly Related Threads…
Thread Author Replies Views Last Post
  Sume Every 10 element in the list and Divided of Sum quest_ 7 270 Nov-27-2020, 10:58 AM
Last Post: perfringo
  Counting Element in Multidimensional List quest_ 1 161 Nov-25-2020, 10:00 PM
Last Post: quest_
  Adding List Element if Second part of the List Elements are the Same quest_ 3 217 Nov-25-2020, 04:33 PM
Last Post: bowlofred
  2d Array adds last element to entire list waiteup 2 180 Nov-19-2020, 08:25 PM
Last Post: bowlofred
  How to get index of minimum element between 3 & 8 in list Mekala 2 230 Nov-10-2020, 12:56 PM
Last Post: DeaD_EyE
  Problem printing last element from a list tester_V 3 272 Oct-30-2020, 04:54 AM
Last Post: tester_V
  Removing items from list if containing a substring pythonnewbie138 2 432 Aug-27-2020, 10:20 PM
Last Post: pythonnewbie138
  Finding an element in a 1d list in a 2d array lionrocker221 0 426 Jun-27-2020, 04:50 PM
Last Post: lionrocker221
  removing dictionary element in list using (key, value) MelonMusk 3 517 Jun-13-2020, 02:37 PM
Last Post: buran
  using element on a list as condition statement glennford49 11 1,015 May-21-2020, 12:53 PM
Last Post: hussainmujtaba

Forum Jump:

User Panel Messages

Announcements
Announcement #1 8/1/2020
Announcement #2 8/2/2020
Announcement #3 8/6/2020