Converting from IEnumerable to List

Question

I want to convert from IEnumerable<Contact> to List<Contact>. How can I do this?

score 541 · Accepted Answer · edited Sep 07 '18 at 20:14

541

You can do this very simply using LINQ.

Make sure this using is at the top of your C# file:

using System.Linq;

Then use the ToList extension method.

Example:

IEnumerable<int> enumerable = Enumerable.Range(1, 300);
List<int> asList = enumerable.ToList();

edited Sep 07 '18 at 20:14

jpaugh

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answered Oct 01 '11 at 02:28

vcsjones

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It is important to note that your solution works for the generic version of `IEnumerable`. The answer from user pickles below handles the non-generic version. – mkmurray Mar 20 '13 at 19:49
3

I wonder if Microsoft changed this. I just tried this very example, and there is no ToList() method in IEnumerable. Using VS 2015 and .NET 4.6.1 . – James Dec 22 '16 at 20:20
3

@James it's an extension method. You may need the "using", but no, they did not change this. – vcsjones Dec 22 '16 at 20:27
1

will it throw an error if my IEnumerable is empty ? – Sumit Joshi Feb 15 '18 at 06:04

score 214 · Answer 2 · answered Oct 01 '11 at 02:30

214

In case you're working with a regular old System.Collections.IEnumerable instead of IEnumerable<T> you can use enumerable.Cast<object>().ToList()

answered Oct 01 '11 at 02:30

cordialgerm

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score 22 · Answer 3 · edited May 23 '17 at 12:03

If you're using an implementation of System.Collections.IEnumerable you can do like following to convert it to a List. The following uses Enumerable.Cast method to convert IEnumberable to a Generic List.

//ArrayList Implements IEnumerable interface
ArrayList _provinces = new System.Collections.ArrayList();
_provinces.Add("Western");
_provinces.Add("Eastern");

List<string> provinces = _provinces.Cast<string>().ToList();

If you're using Generic version IEnumerable<T>, The conversion is straight forward. Since both are generics, you can do like below,

IEnumerable<int> values = Enumerable.Range(1, 10);
List<int> valueList = values.ToList();

But if the IEnumerable is null, when you try to convert it to a List, you'll get ArgumentNullException saying Value cannot be null.

IEnumerable<int> values2 = null;
List<int> valueList2 = values2.ToList();

enter image description here

Therefore as mentioned in the other answer, remember to do a null check before converting it to a List.

score 7 · Answer 4 · answered Nov 26 '14 at 17:45

7

another way

List<int> list=new List<int>();

IEnumerable<int> enumerable =Enumerable.Range(1, 300);  

foreach (var item in enumerable )  
{     
  list.add(item);  
}

answered Nov 26 '14 at 17:45

NourAldienArabian

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It's quite better to use "AddRange(enumerable)" function or List(enumerable) constructor. – QtRoS Sep 22 '15 at 14:41

score 5 · Answer 5 · edited Jan 04 '17 at 05:33

I use an extension method for this. My extension method first checks to see if the enumeration is null and if so creates an empty list. This allows you to do a foreach on it without explicitly having to check for null.

Here is a very contrived example:

IEnumerable<string> stringEnumerable = null;
StringBuilder csv = new StringBuilder();
stringEnumerable.ToNonNullList().ForEach(str=> csv.Append(str).Append(","));

Here is the extension method:

public static List<T> ToNonNullList<T>(this IEnumerable<T> obj)
{
    return obj == null ? new List<T>() : obj.ToList();
}

Converting from IEnumerable to List

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