Return a value when the element is not present in list using linq

I have the following code which would开发者_运维百科 return me a value if it is present in the array "arrayID".

string str = arrayID.Single(s => s == ((System.Data.DataRowView)(e.Item.DataItem)).Row["ID"].ToString());

The problem I'm facing now is that when the value is not present I get the error

Sequence contains no matching element

I would like to have an empty string returned incase the value is not present in arrayID.

Kindly let me know how this can be done in linq.

Thanks in advance.

---

The SingleOrDefault method is what you're after. If no item exists, it will return the default value (null), so you'll just need another step to convert that to empty:

string str = arrayID
    .SingleOrDefault(s => s == ((System.Data.DataRowView)(e.Item.DataItem)).Row["ID"].ToString())
        ?? string.Empty

---

Default in SingleOrDefault refers to the C# default keyword. So when nothing is found the default of the source value is returned.

http://msdn.microsoft.com/en-us/library/xwth0h0d.aspx

So just be aware that the default of a value type will not be null.

For example:

        int[] list = { 1, 3, 7, 13,21};

        int v;
        try {
            v=list.Single(n => n > 15);
        }
        catch (Exception ex) {
            Console.WriteLine(ex.Message);
        }

        int? v2;
        v2 = list.SingleOrDefault(n => n > 30);
        Console.WriteLine(v2.ToString());
        // output: 0

        int v3;
        v3=list.SingleOrDefault(n => n > 30);            
        Console.WriteLine(v3.ToString());
        // output: 0

        string[] slist = {"a", "b", "c"};
        var v4 = slist.SingleOrDefault(s => s == "z");
        Console.WriteLine(v4==null);
        // output: true     <-- i.e. it is a reference type + it is nullable.