Select Multiple Fields from List in Linq

Question

Anonymous types allow you to select arbitrary fields into data structures that are strongly typed later on in your code:

var cats = listObject
    .Select(i => new { i.category_id, i.category_name })
    .Distinct()
    .OrderByDescending(i => i.category_name)
    .ToArray();

Since you (apparently) need to store it for later use, you could use the GroupBy operator:

Data[] cats = listObject
    .GroupBy(i => new { i.category_id, i.category_name })
    .OrderByDescending(g => g.Key.category_name)
    .Select(g => g.First())
    .ToArray();

var selectedCategories =
    from value in
        (from data in listObject
        orderby data.category_name descending
        select new { ID = data.category_id, Name = data.category_name })
    group value by value.Name into g
    select g.First();

foreach (var category in selectedCategories) Console.WriteLine(category);

Edit: Made it more LINQ-ey!

You could use an anonymous type:

.Select(i => new { i.name, i.category_name })

The compiler will generate the code for a class with name and category_name properties and returns instances of that class. You can also manually specify property names:

i => new { Id = i.category_id, Name = i.category_name }

You can have arbitrary number of properties.

This is task for which anonymous types are very well suited. You can return objects of a type that is created automatically by the compiler, inferred from usage.

The syntax is of this form:

new { Property1 = value1, Property2 = value2, ... }

For your case, try something like the following:

var listObject = getData();
var catNames = listObject.Select(i =>
    new { CatName = i.category_name, Item1 = i.item1, Item2 = i.item2 })
    .Distinct().OrderByDescending(s => s).ToArray();

You can select multiple fields using linq Select as shown above in various examples this will return as an Anonymous Type. If you want to avoid this anonymous type here is the simple trick.

var items = listObject.Select(f => new List<int>() { f.Item1, f.Item2 }).SelectMany(item => item).Distinct();

I think this solves your problem

You can make it a KeyValuePair, so it will return a "IEnumerable<KeyValuePair<string, string>>"

So, it will be like this:

.Select(i => new KeyValuePair<string, string>(i.category_id, i.category_name )).Distinct();