Question

If I have a list like this:

var teams = new List() { "Team A", "Team B", "Team C" };

And I have a data set with scores like this:

var scores = new List<scoredata> {
    new scoredata() { Team = 'Team A', Date = '1/1/2012', Value = 1 }, 
    new scoredata() { Team = 'Team B', Date = '1/1/2012', Value = 1 }, 
    new scoredata() { Team = 'Team C', Date = '1/1/2012', Value = 1 }, 
    new scoredata() { Team = 'Team A', Date = '1/2/2012', Value = 2 }, 
    new scoredata() { Team = 'Team B', Date = '1/3/2012', Value = 3 }, 
    new scoredata() { Team = 'Team C', Date = '1/4/2012', Value = 4 }
}

Is it possible to construct a data set that looks like this?

Team A, '1/1/2012', 1
Team B, '1/1/2012', 1
Team C, '1/1/2012', 1
Team A, '1/2/2012', 2
Team B, '1/2/2012', null
Team C, '1/2/2012', null
Team A, '1/3/2012', null
Team B, '1/3/2012', 3
Team C, '1/3/2012', null
Team A, '1/4/2012', null
Team B, '1/4/2012', null
Team C, '1/4/2012', 4

I’m not sure what this is called, but I want to fill out blank dates and scores in my final dataset so that it always returns all Teams for each date, but if score data is not available returns null.

Answer 1

Using pure LINQ to Objects.

public class ScoreData
{
    public string Team { get; set; }
    public string Date { get; set; }
    public int? Value { get; set; }
}

var teams = new[] { "Team A", "Team B", "Team C" };
var scores = new[]
{
    new ScoreData { Team = "Team A", Date = "1/1/2012", Value = 1 }, 
    new ScoreData { Team = "Team B", Date = "1/1/2012", Value = 1 }, 
    new ScoreData { Team = "Team C", Date = "1/1/2012", Value = 1 }, 
    new ScoreData { Team = "Team A", Date = "1/2/2012", Value = 2 }, 
    new ScoreData { Team = "Team B", Date = "1/3/2012", Value = 3 }, 
    new ScoreData { Team = "Team C", Date = "1/4/2012", Value = 4 },
};

var dates = scores.Select(score => score.Date).Distinct();
var query =
    from date in dates
    from team in teams
    join score in scores
        on new { Team = team, Date = date }
        equals new { score.Team, score.Date }
        into filteredScores
    let defaultScore = new ScoreData
    {
        Team = team,
        Date = date,
        Value = null,
    }
    from score in filteredScores.DefaultIfEmpty(defaultScore)
    select score;

Note, this most likely won’t work as-is in LINQ to SQL or LINQ to Entities, it will need some tweaks.