Python Forum
deleting select items from a list
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
deleting select items from a list
#11
Is there a reason you can't use lazy sequences? It would really help if you showed code for what you're doing. It's difficult to discuss hypothetical things.
Reply
#12
(Oct-10-2021, 05:00 AM)ndc85430 Wrote: Is there a reason you can't use lazy sequences? It would really help if you showed code for what you're doing. It's difficult to discuss hypothetical things.

this is about doing lazy evaluation, for me. the code i have is big and complicated due to so much other stuff in it. i have no simple code that gets to the root of the matter, i have some potential directions to go. iterating the list in reverse, as was suggested is one of many. it could be done many ways. one of the ways could include for x in range(len(the_list)-1,-1,-1): (i like variable name x, think: index). if i delete the_list[x] inside the body of this for loop, it does not affect the iteration as the range iterator is now independent of the actual list and x only moves to non-mutated parts of the list. another approach i am considering is: instead of deleting the item in the list, store None in its place and change the code that uses the list to evaluate the list by treating None as absent data. and, sure, i could do that as its own iterator in many cases.

i did not mention these ideas up front because i did not want to have any bias by this in the ideas others might offer. instead of discussing limited to my ideas, i want to see if there are other ideas and if any of the others might be treated as more significant.
Tradition is peer pressure from dead people

What do you call someone who speaks three languages? Trilingual. Two languages? Bilingual. One language? American.
Reply
#13
(Oct-10-2021, 06:11 PM)Skaperen Wrote: one of the ways could include for x in range(len(the_list)-1,-1,-1): (i like variable name x, think: index). if i delete the_list[x] inside the body of this for loop
Yes to make code more ugly and less readable could do that 🧺
names = ["Alice", "Bob", "Andrew", "Charlie"]
for item in range(len(names)-1,-1,-1):
    if not names[item].startswith('A'):
        del names[item]
print(names)
Output:
['Alice', 'Andrew']
It's faster than remove() solution,but still slower than:
names = ["Alice", "Bob", "Andrew", "Charlie"]
names = [name for name in names if name.startswith('A')]
print(names)
Output:
['Alice', 'Andrew']
If think in place is cool,so is there a way with this the last one.
names = ["Alice", "Bob", "Andrew", "Charlie"]
print(id(names))
names[:] = [name for name in names if name.startswith('A')]
print(names)
print(id(names))
Output:
2496125597184 ['Alice', 'Andrew'] 2496125597184
Skaperen likes this post
Reply
#14
tusen takk!

in a couple cases i do need to really do it in place because the code using the list called the code that will change the list. of course, that is not a proper way to do things but it is the only context to avoid the time (testing everything) to re-implement a big script.
Tradition is peer pressure from dead people

What do you call someone who speaks three languages? Trilingual. Two languages? Bilingual. One language? American.
Reply


Possibly Related Threads…
Thread Author Replies Views Last Post
  Getting All Items From A List knight2000 4 448 Sep-25-2021, 12:56 AM
Last Post: knight2000
  Feed List items with Integer euras 9 1,290 May-19-2021, 07:45 PM
Last Post: snippsat
  Parse String between 2 Delimiters and add as single list items lastyle 5 1,092 Apr-11-2021, 11:03 PM
Last Post: lastyle
  Sum of list items tristanfermat 2 820 Feb-06-2021, 12:04 PM
Last Post: tristanfermat
  Deleting employee from list SephMon 3 921 Jan-05-2021, 04:15 AM
Last Post: deanhystad
  Count number of occurrences of list items in list of tuples t4keheart 1 931 Nov-03-2020, 05:37 AM
Last Post: deanhystad
  concatenating 2 items at a time in a python list K11 3 916 Oct-21-2020, 09:34 AM
Last Post: buran
  Select the other of 2 items in a list Clunk_Head 7 1,438 Sep-01-2020, 05:27 PM
Last Post: Clunk_Head
  Removing items from list if containing a substring pythonnewbie138 2 931 Aug-27-2020, 10:20 PM
Last Post: pythonnewbie138
  Select correct item from list for subprocess command pythonnewbie138 6 1,306 Jul-24-2020, 09:09 PM
Last Post: pythonnewbie138

Forum Jump:

User Panel Messages

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