Delete item from arraylist

Question

In my programm I have a List of Strings and a List of integer values which should be deleted from the first list. Think of somehing like this:

ArrayList<String> items = new ArrayList<String>();
items.add("A"); items.add("B"); items.add("C");

ArrayList<Integer> del = new ArrayList<Integer>();
del.add(1); del.add(2);

Of course I can loop throught the list with this code and delete the items:

for (int i = 0; i < del.size(); i++) 
{
    items.remove(del.get(i));
}

But here is the problem. After the first element is deleted the index is shifted so I delete the wrong items. Is there a graceful solution for this?

what is this ArrayList<Integer> del = new ArrayList<String>(); — Nambi
– Nambi, Commented Feb 25, 2014 at 13:00
Of course you are right. Thanks for that. So easy solution... — Cilenco
– Cilenco, Commented Feb 25, 2014 at 13:01
ArrayList<Integer> del = new ArrayList<String>(); <-- this will not compile — fge
– fge, Commented Feb 25, 2014 at 13:01

qqilihq · Accepted Answer · 2014-02-25 13:10:10Z

3

Sort the deletion list in a descending order and then iterate:

Collections.sort(del, Collections.reverseOrder());
for (Integer toDelete : del) {
    // casting to int, because you need #remove(int), not #remove(Object)
    items.remove((int)toDelete);
}

[edit] Fixed. Sorry, this was twice reversed at the beginning.

[edit2] Added necessary cast :)

edited Feb 25, 2014 at 13:10

answered Feb 25, 2014 at 13:01

qqilihq

11.5k9 gold badges58 silver badges96 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Thom Over a year ago

Great answer, didn't think of that. Also, please note my answer about using a problem domain key instead of the index.

Cilenco Over a year ago

Question to edit2: Shouldn't Java pack/unpack the wrapper by itself?

qqilihq Over a year ago

No, as there is also a #remove(Object) method, this one has precedence, if not casting explicitly; the #remove(Object) method would try to remove an Object from the list, for which equals(Object) is true; #remove(int) on the other hand removes by index, which is what you want.

Jason C · Accepted Answer · 2014-02-25 13:04:51Z

1

You have a few options, but two of the simpler ones are:

Delete the largest indices first. Sort your index list in descending order before you do this.
If sorting the index list is not feasible for some reason and your string list doesn't usually contain null, first replace all the items you want to delete with null then remove all nulls from the string list (e.g. while (items.remove(null)) ;).

answered Feb 25, 2014 at 13:04

Jason C

40.6k16 gold badges136 silver badges201 bronze badges

Comments

Thom · Accepted Answer · 2014-02-25 13:01:13Z

0

Graceful? I don't think so. A working solution would be to make sure your del list is sorted and then go through and decrement all following indexes so they sync back up.

A better solution would be to use a key that is endemic to the problem domain for your deletes instead of the index into the array. That would be a graceful solution.

answered Feb 25, 2014 at 13:01

Thom

15.3k34 gold badges117 silver badges201 bronze badges

1 Comment

Jason C Over a year ago

Your suggestion about the key is a good one. However, for the first idea, the indexes wouldn't need to be sync'd if the index list was sorted in descending order.

Collectives™ on Stack Overflow

Delete item from arraylist

3 Answers 3

3 Comments

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related