如何将通用列表投影到字典中？

Question

Is there a simple, LINQ-only way to project a generic collection into a Dictionary, something which would eliminate the foreach in the following code block:

    Dictionary<int, Player> _rankedPlayers = new Dictionary<int,Player>();
    List<Player> rankedPlayers = Player.GetPlayers(Globals.FOOString, seasonCode);
    int i = 1;
    foreach (Player targetPlayer in rankedPlayers)
    {
      _rankedPlayers.Add(i, targetPlayer);
    }

Answer 1

You are looking for ToDictionary method

var _rankedPlayers = Player.GetPlayers(Globals.FOOString, seasonCode)
      .Select((item, index) => new { item, index })
      .ToDictionary(x => index, x => x.item);

Answer 2

You can use the overload method of Enumerable.Select that produces an index of the element and project it into a dictionary using Enumerable.ToDictionary :

var rankedPlayers = Player.GetPlayers(Globals.FOOString, seasonCode)
    .Select((item, index) => Tuple.Create(item, index))
    .ToDictionary(item => item.Item1 + 1, item => i.Item2);

If your player list is too long, you might not feel comfortable creating a lot of Tuple instances and use an external index:

var i = 0;
var rankedPlayers = Player.GetPlayers(Globals.FOOString, seasonCode)
    .ToDictionary(i => ++i, item => item.Item2);

Although this approach creates a new class for the closure over i .

If this is still too much for you, you can create your own extension:

public static class MyExtensions
{
    public static Dictionary<int, TSource> ToDictionary<TSource>(
        this IEnumerable<TSource> source)
    {
        var dictionary = new Dictionary<int, TSource>();
        var i = 0;
        foreach(var item in source)
        {
            dictionary.Add(++i, item);
        }
        return dictionary;
    }
}

But if you're using it only once, I would do it just like you did.