CODEWITHSUNDEEP
c#
eugeneK
eugeneK

Reputation: 11116

How to remove x items from collection using LINQ?

Is there a way to remove all items except first one from any type of collection (Control.Items, List ....) using LINQ only ?

Upvotes: 2

Views: 3846

Answers (6)

Adilson de Almeida Jr
Adilson de Almeida Jr

Reputation: 2755

listXpto.Where(x=>true /* here goes your query */)
    .Select(x=>{listXpto.Remove(x); return null})

But I don´t know the real utility of that.

Remember that the remove method is for ILists, not IQueryable in general.

Upvotes: 0

Vlad
Vlad

Reputation: 18633

How about something using reflection?

static void RemoveButFirst(object o){

    Type t = o.GetType();

    System.Reflection.MethodInfo rm = t.GetMethod("RemoveAt",
                                                 new Type[]{typeof(int)});
    System.Reflection.PropertyInfo count = t.GetProperty("Count");

    for (int n = (int)(count.GetValue(o,null)) ; n>1; n--)
        rm.Invoke(o, new object[]{n-1});

}

This would work any time your collection exposed an int Count property and a RemoveAt(int) method, which I think those collections should.

And a more concise version, using dynamic, if you work with C# 4.0:

public static void RemoveBut(dynamic col, int k){
    for (int n = col.Count; n>k; n--)
        col.RemoveAt(n-1);
}

Upvotes: 2

dtb
dtb

Reputation: 217253

No. LINQ is designed for querying collections (no side-effects), not for adding or removing items.

What you can do is write a query that takes the first element of the collection:

var result = source.Take(1);

Note that LINQ doesn't work with all types of collections; you need a LINQ provider to make LINQ work. For instance, source must implement IEnumerable<T> to use the extension methods of the Enumerable Class (LINQ-to-Objects).

Upvotes: 4

shenhengbin
shenhengbin

Reputation: 4294

        List<string> collection = new List<string>();
        collection.RemoveAll(p => p.StartsWith("something"));

Upvotes: 0

Bas Slagter
Bas Slagter

Reputation: 9929

How about (in linq):

var result = list.Where(l => l != list.First());

But this would be better:

var result = list.Take(1);

Upvotes: 0

Jesse van Assen
Jesse van Assen

Reputation: 2290

You can use .Take(1), but it returns a new collection, and leaves the original intact.

The idea of LINQ came from functional programming where everything is immutable, because of that, they didn't make it possible to modify the collections with LINQ.

Jon Skeet has a comment on the subject: LINQ equivalent of foreach for IEnumerable<T>

Upvotes: 0

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