Can I select multiple objects in a Linq query

Question

Can I return more than one item in a select? For instance I have a List of Fixtures (think football (or soccer for the yanks) fixtures). Each fixture contains a home and away t

Answer 1

Taking a stab at this myself I came up with the same version as 'it depends'.

Using query comprehension syntax:

IEnumerable<Team> drew =
    from fixture in fixtures
    where fixture.Played && (fixture.HomeScore == fixture.AwayScore)
    from team in new[]{fixture.AwayTeam, fixture.HomeTeam}
    select team;

Using lambda with extension methods:

IEnumerable<Team> drew =
    fixtures.Where(f => f.Played && f.HomeScore == f.AwayScore)
    .SelectMany(f => new[]{f.HomeTeam, f.AwayTeam});

Edit: I don't know if a team could have possibly played and drawn more than once in your database, but if that's possible, then you might want to make use of the Distinct query operator:

IEnumerable<Team> drew =
    (from fixture in fixtures
     where fixture.Played && (fixture.HomeScore == fixture.AwayScore)
     from team in new[]{fixture.AwayTeam, fixture.HomeTeam}
     select team).Distinct();

or:

IEnumerable<Team> drew =
    fixtures.Where(f => f.Played && f.HomeScore == f.AwayScore)
    .SelectMany(f => new[]{f.HomeTeam, f.AwayTeam})
    .Distinct();

Answer 2

Or you can define a type to hold all that data:

IEnumerable<TeamCluster> drew = from fixture in fixtures
                         where fixture.Played && (fixture.HomeScore == fixture.AwayScore)
                         select new TeamCluster {
                             Team1 = fixture.HomeTeam,
                             Team2 = fixture.AwayTeam,
                             Score1 = fixture.HomeScore,
                             Score2 = fixture.AwayScore
                         };

class TeamCluster {
    public Team Team1 { get; set; }
    public Team Team2 { get; set; }
    public int Score1 { get; set; }
    public int Score2 { get; set; }
}

Answer 3

I think you're looking for the Union method as follows:

IEnumerable<Team> drew = (from fixture in fixtures
                     where fixture.Played 
                        && (fixture.HomeScore == fixture.AwayScore)
                     select fixture.HomeTeam)
                     .Union(from fixture in fixtures
                     where fixture.Played 
                        && (fixture.HomeScore == fixture.AwayScore)
                     select fixture.AwayTeam);

Answer 4

I came up against this very issue, and couldn't find what I wanted so I wrote a small extension method which did what I wanted.

public static IEnumerable<R> MapCombine<M, R>(this IEnumerable<M> origList, params Func<M, R>[] maps)
{
    foreach (var item in origList)
    foreach (var map in maps)
    {
        yield return map(item);
    }
}

Following the problem in the question, you would then do something like this

var drew = fixtures.Where(fixture => fixture.Played && 
                        (fixture.HomeScore == fixture.AwayScore))
                    .MapCombine(f => f.HomeTeam, f => f.AwayTeam);

Interestingly intellisense isn't exactly happy about this, you don't get the lamdba expression in the top of the drop down, however after the '=>' its quite happy. But the main thing is the compiler is happy.

Answer 5

Edit: Sorry, misunderstood your original question, so rewrote answer.

You could use the "SelectMany" operator to do what you want:

IEnumerable<Team> drew =
           (from fixture in fixtures
            where fixture.Played && (fixture.HomeScore == fixture.AwayScore)
                  select new List<Team>()
                             { HomeTeam = fixture.HomeTeam,
                               AwayTeam = fixture.AwayTeam
                             }).SelectMany(team => team);

This will return a flattened list of teams that drew.

Answer 6

101 LINQ Samples, namely Select - Anonymous Types 1

... select new { HomeTeam = fixture.HomeTeam, AwayTeam = fixture.AwayTeam };