如何使用Linq代替foreach进行分组和计数

Question

I have 2 Lists, one for Players and another for Coaches.

To count number of Players belong to a Coach, I used:

  var g = AllePlayer.GroupBy(play=> play.coachNumer);
  foreach (var grp in g)
  {
      foreach (Coach co in AlleCoaches)
      {
          if (co.coachNumer== grp.Key)
          {
              co.NumOfPlayer= grp.Count();
          }
       }
  }

Now I want to know if there is a nice way to put the lover parts with "foreach" in a nice Linq syntax to avoid this "foreach" loops. Thank you in advance!

Answer 1

You could change the statement around a little bit. Since ultimately you want to change a property on each coach, it's easiest to loop through that list, as in:

foreach (Coach co in AlleCoaches)
{
    co.NumOfPlayer= AllePlayer.Where(p => p.coachNumber == co.coachNumber)
                              .Count();
}

Answer 2

This would be a simpler approach:

var query = AllePlayer.GroupBy(player => player.coachNumer,
                               (coach, players => new {
                                   Coach = coach,
                                   Count = players.Count() }));

That will give you a sequence where each element is the coach and the number of players for that coach.

Then you could iterate over the result, and assign the value into Coach.NumOfPlayer , but do you really need to? If you do, this will do it:

foreach (var pair in query)
{
    pair.Coach.NumOfPlayer = pair.Count;
}

Personally it doesn't feel like "number of players" should be part of the Coach type to start with...

Answer 3

AlleCoaches.ToList()
.ForEach(n=>n.NumOfPlayer=AllePlayer.Where(n=>coachNumer==n.coachNumer).Count());

Answer 4

var g = AllePlayer.TakeWhile(play=> ( play.coachNumer!=null));

您可以采用所需的任何逻辑，但是语法相同。

var count = g.Count();