从条件清单中取出N个物品

Question

I have the following:

IDictionary<QuestionDuration, Int32> rules = _service.GetRules(); 

List<Question> questions = _service.GetQuestions();

public class Question {
  public QuestionDuration Duration { get; set; }
}

The dictionary values (Int32) are the number of questions I need to take from the list with that specific duration ... So if I have the dictionary:

{ { QuestionDuration.M2, 5 }, { QuestionDuration.M4, 3 }, { QuestionDuration.M8, 0 }, ...

So I need to create a List from the original list with 5 questions of 2 minutes, 4 questions of 3 minutes, 0 questions of 8 minutes, etc ...

I was trying to group and use a lambda expression for this but I wasn't able ...

How can I do this?

Thank You,

Miguel

Answer 1

That will create IEnumerable<List<Question>> (three lists for your dictionary of rules):

IDictionary<QuestionDuration, Int32> rules = _service.GetRules();
List<Question> questions = _service.GetQuestions();

var query = from r in rules
            select questions.Where(q => q.Duration == r.Key)
                            .Take(r.Value).ToList();

Tip: if you need to pick random questions in each list, then add OrderBy(q => Guid.NewGuid()) just before Take operator. Or more random solution:

var rand = new Random();
var query = from r in rules
            select questions.Where(q => q.Duration == r.Key)
                            .OrderBy(q => rand.Next())
                            .Take(r.Value).ToList();