How to convert System.Linq.Enumerable.WhereListIte

问题:

In the below example, how can I easily convert eventScores to List<int> so that I can use it as a parameter for prettyPrint?

Console.WriteLine("Example of LINQ's Where:");
List<int> scores = new List<int> { 1,2,3,4,5,6,7,8 };
var evenScores = scores.Where(i => i % 2 == 0);

Action<List<int>, string> prettyPrint = (list, title) =>
    {
        Console.WriteLine("*** {0} ***", title);
        list.ForEach(i => Console.WriteLine(i));
    };

scores.ForEach(i => Console.WriteLine(i));
prettyPrint(scores, "The Scores:");
foreach (int score in evenScores) { Console.WriteLine(score); }

回答1:

You'd use the ToList extension:

var evenScores = scores.Where(i => i % 2 == 0).ToList();

回答2:

var evenScores = scores.Where(i => i % 2 == 0).ToList();

Doesn't work?

回答3:

By the way why do you declare prettyPrint with such specific type for scores parameter and than use this parameter only as IEnumerable (I assume this is how you implemented ForEach extension method)? So why not change prettyPrint signature and keep this lazy evaluated? =)

Like this:

Action<IEnumerable<int>, string> prettyPrint = (list, title) =>
{
    Console.WriteLine("*** {0} ***", title);
    list.ForEach(i => Console.WriteLine(i));
};

prettyPrint(scores.Where(i => i % 2 == 0), "Title");

Update:

Or you can avoid using List.ForEach like this (do not take into account string concatenation inefficiency):

var text = scores.Where(i => i % 2 == 0).Aggregate("Title", (text, score) => text + Environment.NewLine + score);