Question

List<Foo> fooList = new List<Foo>();

fooList.Add(new Foo(){
    Id = 1,
    Bar = 1,
    Blah = 1
});

fooList.Add(new Foo(){
    Id = 1,
    Bar = 2,
    Blah = 1
});

fooList.Add(new Foo(){
    Id = 2,
    Bar = 1,
    Blah = 2
});

If I group my fooList by the Id property, all properties except Bar are equal to each other for each group. I noticed that there is a GroupMy lambda method, but is there any way to group the lists by Id, and make the Bar property a list of all the Bars for each id?

Because right now i have a lot of redundant data on each row. Please let me know if you want me to elaborate the problem.

Answer 1

Use the GroupBy extension that lets you determine the element selector:

var query = fooList.GroupBy(f => f.Id, f => f.Bar);

// Iterate over each grouping in the collection. 
foreach (var group in query)
{
    // Print the key value.
    Console.WriteLine(group.Key);
    // Iterate over each value in the  
    // grouping and print the value. 
    foreach (int bar in group)
        Console.WriteLine("  {0}", bar);
}

Or if you want Bar to be an explicit property:

var query = fooList.GroupBy(
    f => f.Id, 
    (id, foos) => new {Id = id, Bars = foos.Select(f=>f.Bar)});

Though I find that a little hard to read.