How to delete objects from array using LINQ

Question

I have an array of objects of type A: A[] ar. And a list of integers: List<int> indexes.

How can I delete from the ar all objects with indexes in the indexes, using LINQ? I.e. I need a new (smaller) array without the objects that their indexes are in indexes. Using LINQ.

Is the order of the remained objects will be the same as before the deletion?

Thanks a lot.

Do you want to get new Array as a result? Arrays are immutable, you only can set NULL instead of reference to an object — opewix
– opewix, Commented Jul 16, 2017 at 9:52
@opewix It's not enough for me just to set null, I need a new (smaller) array without the objects that their indexes are in "indexes". — Ilan
– Ilan, Commented Jul 16, 2017 at 9:56

Richard · Accepted Answer · 2017-07-16 09:59:39Z

2

You cannot modify an array only the elements it contains.

But you can easily create a replacement array:

myArray = myArray.Where(x => x.KeepThisElement).ToArray();

With LINQ to Objects (which you'll be using in this case) there in an overload of Where that passes the current index to the predicate:

myArray = myArray.Where((x, idx) => !indexes.Conatins(idx)).ToArray();

answered Jul 16, 2017 at 9:59

Richard

110k21 gold badges214 silver badges279 bronze badges

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

2 Comments

Ilan Over a year ago

Is the order of the remained objects will be the same as before the deletion? Thank you.

Richard Over a year ago

@Ilan Yes, the input enumerable is processed in order.

opewix · Accepted Answer · 2017-07-16 09:58:18Z

1

This may look odd, but it does what you want (it's not a LINQ):

var filtered = new List<A>();
for (var i = 0; i < ar.Length; i++)
{
    if (indexes.Contains(i))
        continue;

    filtered.Add(ar[i]]);
}

var ar = filtered.ToArray();

If your integer list is very big, consider to use HashSet<int> instead of list to get more performance

answered Jul 16, 2017 at 9:58

opewix

5,1031 gold badge22 silver badges43 bronze badges

1 Comment

Ilan Over a year ago

@openwix Thanks.. The non-linq version is indeed quite simple. But I'd like to do the same thing using LINQ query. If it's possible, of course.

Collectives™ on Stack Overflow

How to delete objects from array using LINQ

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related