Linq Select as for loop condition C#

Question

So, I have a list of integers called itemIds and a list of objects called items, how can I rewrite this :

 List<int> itemIds;
 List<object> items;

 for (itemIds.Select(old => (!items.Any(i => i.itemId == old))))
    {
          ItemService.ItemDeleteById(old);
    }

Now it fails, it asks for ";" after the last paranthesis of the for and it doesn't recognize the old variable.I want to delete the items that meet that condition. Thanks !

`for` requires a start condition, end condition, and an increment step, you are missing 2 of the 3. — Ron Beyer, Aug 30 '18 at 14:18
The answers below will work for your current pattern. My question is if itemIds appear to be unique enough for deletion, why are you storing them in a `List` and not a `Dictionary`? — Parrish Husband, Aug 30 '18 at 14:21
And the mandatory reference to the Microsoft Docs: [for statement](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/for). The correct syntax is : `for (; ; )` — Drag and Drop, Aug 30 '18 at 14:36

score 1 · Answer 1 · answered Aug 30 '18 at 14:18

1

You can use foreach. Also use .Where() instead of .Select():

foreach (var itemId in itemIds.Where(old => !items.Any(i => i.itemId == old)))
{
    ItemService.ItemDeleteById(itemId);
}

answered Aug 30 '18 at 14:18

Peter B

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score 1 · Answer 2 · answered Aug 30 '18 at 14:30

1

If you hashed itemIds, you'll probably have a more performant loop:

HashSet<int> itemIds;
List<object> items;

foreach (var item in items.Where(i => itemIds.Contains(i.itemId))
{
   ItemService.ItemDeleteById(item.itemId);
}

answered Aug 30 '18 at 14:30

Parrish Husband

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score 1 · Answer 3 · answered Aug 30 '18 at 14:33

1

You can write it as:

foreach(var x in itemsIds.Where(old => items.Contains(old)){
        ItemService.ItemDeleteById(x);
    }

EDIT: Outspeedded by Parrish Husband

answered Aug 30 '18 at 14:33

Kerlos Bekhit

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7

score 0 · Accepted Answer · answered Aug 30 '18 at 14:18

0

try foreach instead of for and Select doesn't receive a predicate true/ false, use Where instead

foreach (var item in itemIds.Where(old => !items.Any(i => i.itemId == old)))
    {
          ItemService.ItemDeleteById(item);
    }

answered Aug 30 '18 at 14:18

Antoine V

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Linq Select as for loop condition C#

4 Answers4