LINQ: Selecting Multiple Properties from a List of Objects


In a previous post I discussed how to use LINQ to flatten a list of lists. Yesterday and ran across a slightly different situation but that used the same solution.

I had a list of objects that each contained three separate integer values and I wanted to extract the three values from each object and put them all in a single list. So, all you need to do is create a new List that has each of the three values in each object as elements of the list and then use the SelectMany method to flatten the list of lists we just created.

private class Foo
{
    public int Item1;
    public int Item2;
    public int Item3;
}

static void Main(string[] args)
{
    List<Foo> foos = new List<Foo> 
                           { 
                               new Foo() { Item1 = 1, Item2 = 2, Item3 = 3 },
                               new Foo() { Item1 = 4, Item2 = 5, Item3 = 6 },
                               new Foo() { Item1 = 7, Item2 = 8, Item3 = 9 }
                           };

    // Create a list of lists where each list has three elements corresponding to 
    // the values stored in Item1, Item2, and Item3.  Then use SelectMany
    // to flatten the list of lists.
    var items = foos.Select(f => new List<int>() { f.Item1, f.Item2, f.Item3 }).SelectMany(item => item).Distinct();

    foreach (int item in items)
        Console.WriteLine(item.ToString());
    
    Console.ReadLine();
}

// Output
// ------
// 1
// 2
// 3
// 4
// 5
// 6
// 7
// 8
// 9
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Posted in LINQ. Tags: , . 2 Comments »

2 Responses to “LINQ: Selecting Multiple Properties from a List of Objects”

  1. handcraftsman Says:

    This can be shortened a bit to:

    var items = foos
    .SelectMany(f => new []{ f.Item1, f.Item2, f.Item3 })
    .Distinct();

    • Nick Olsen Says:

      Thanks for the tip! After some testing on large collections, albeit predictable, your method also proves to be a bit faster as well.


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