Remove a specific item from a list using LINQ

Question

I have a list containing some objects and want to use LINQ to remove a specific item but am not sure how to do that.

foreach (var someobject in objectList)
{
    if (someobject.Number == 1) // There will only one item where Number == 1.  
    {
        list.remove(someobject)
    } 
}

Contrary to what you are claiming, your current code does not involve LINQ at all. Do you have specific reasons for wanting/needing a LINQ-based solution? Or would any other efficient solution be acceptable, too? — stakx - no longer contributing, Nov 28 '14 at 20:22
@VsevolodGoloviznin: The above code cannot possibly work, because it contains syntax errors – `list.remove(someobject)`. — stakx - no longer contributing, Nov 28 '14 at 20:22
What is `list` and `objectList`? Are they both meant to be same variables or what? And what is the problem with the current code? — Sriram Sakthivel, Nov 28 '14 at 20:23
@stakx well, yes, I though it was just a typo, anyway if it is the code should work, though it's not optimal — Vsevolod Goloviznin, Nov 28 '14 at 20:25
Does this answer your question? [Using LINQ to remove elements from a List](https://stackoverflow.com/questions/853526/using-linq-to-remove-elements-from-a-listt) — Michael Freidgeim, Oct 30 '19 at 06:24

score 29 · Accepted Answer · edited May 23 '17 at 12:34

You cannot use a foreach to remove items during enumeration, you're getting an exception at runtime.

You could use List.RemoveAll:

list.RemoveAll(x => x.Number == 1);

or, if it's actually not a List<T> but any sequence, LINQ:

list = list.Where(x => x.Number != 1).ToList();

If you are sure that there is only one item with that number or you want to remove one item at the maximum you can either use the for loop approach suggested in the other answer or this:

var item = list.FirstOrDefault(x => x.Number == 1);
if(item ! = null) list.Remove(item);

The link to the other question i have posted suggests that you can modify a collection during enumeration in C# 4 and later. No, you can't. That applies only to the new concurrent collections.

In this case you could actually use a foreach since there's only one item to remove. Just make sure to use break to go out of the loop after the item has been removed, otherwise you'll get an exception on the next iteration. That said, I think the solution with RemoveAll() is more elegant. — haagel, Nov 17 '17 at 10:53

mybirthname · Answer 2 · 2018-01-05T16:29:04.400

4

You can't use foreach to remove item from collection. This will throw an exception that the collection is modified.

You can perform it with for

for (int i=objectList.Count-1; i>=0 ; i--)
{
    if (objectList[i].Number == 1) // there will only one item with Number = 1   
    {
       objectList.Remove(objectList[i]);
    } 
}

Other case is to use Remove/RemoveAll like Tim Schmelter show.

edited Jan 05 '18 at 16:29

answered Nov 28 '14 at 20:22

mybirthname

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As pointed out elsewhere, if you're happy to `break` after you find a match, there's no reason to switch the `foreach` loop to a `for` loop. – Rawling Jan 05 '18 at 07:48
1

@Rawling some other guy added the break statement. Anyway, the answer at the beginning was not good too. – mybirthname Jan 05 '18 at 16:28

score 2 · Answer 3 · answered Nov 17 '17 at 10:47

You CAN use a foreach loop to remove an item from a list. The important thing is to use break to stop the loop once you have removed the item. If the loop continues after an item is removed from the list, an exception will be thrown.

foreach (var someobject in objectList)
{
    if (someobject.Number == 1) // There will only one item where Number == 1
    {
        objectList.remove(someobject);
        break;
    } 
}

However, this will ONLY work if there's only one object you want to remove, as in your case.

score -1 · Answer 4 · answered Nov 28 '14 at 20:34

-1

you could remove at the index if the value meets the criteria

for (int i=0; i < objectList.Count; i ++)
{
    if (objectList[i].Number == 1) // there will only one item with Number = 1   
    {
       objectList.RemoveAt[i];
    } 
}

answered Nov 28 '14 at 20:34

SuncoastOwner

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Remove a specific item from a list using LINQ

4 Answers4