Creating a list by matching/combining items from two separate list

Question

The statement below works fine when both the AwayRecord and HomeRecord objects returns every team associated with the Teams object, but there are times when this will not be the case. For example, the Teams object will always return 30 items, while the AwayRecord may return 28, and the HomeRecord 29. I would like to specifically match the AwayRecord and HomeRecord items to the matching team items from the Teams object. Where there are no matching items from either the AwayRecord or HomeRecord with the Teams object, I would like to retain the team name from the the Teams object and just set the remaining properties to null or 0.

List<MLBrst> mlbStandings = Teams.Select((t, i) => new MLBrst
(t.Abreviated_Short, AwayRecord[i], HomeRecord[i])).AsEnumerable().ToList();

// MLBrst constructor
public MLBrst(string team, MLBrst ar, MLBrst hr)
{
Team = team;
Wins = ar.Wins + hr.Wins;
Losses = ar.Losses + hr.Losses;
Spread = (ar.Spread + hr.Spread) / (Wins + Losses);
Total = (ar.Total + hr.Total) / (Wins + Losses);
GP = Wins + Losses;
RS = ar.RS + hr.RS;
RA = ar.RA + hr.RA;
PD = RS - RA;
}

Thanks in advance.

Vulpes · Answer

You could make it slightly more concise and efficient by not creating the two temporary lists atMissing and htMissing but enumerating the IEnumerable 's directly: // Check to see if the teams indexes match. If not then add missing teams. if (TeamsIndex != AwayTeams.Count()) { foreach (string item in TotalTeams.Except(AwayTeams)) { AwayRecord.Add(new MLBrst { Team = item Losses = 0 Spread = 0m Total = 0m }); } } if (TeamsIndex != HomeTeams.Count()) { foreach (string item in TotalTeams.Except(HomeTeams)) { HomeRecord.Add(new MLBrst { Team = item Losses = 0 Spread = 0m Total = 0m }); } }

Vulpes · Answer

Ah if the AwayRecord and HomeRecord objects have the same number of elements as the Teams object (i.e. 30) except that some of those elements may be null then the problem is much easier because you're original query will still work as long as you change the constructor in the way that I've suggested. This will then cope with possible null values for the last two arguments without throwing an exception.

Vulpes · Answer

If I've understood that correctly I'd try changing your query to this: List mlbStandings = Teams.Select((t i) => { if (i { return new MLBrst(t.Abreviated_Short AwayRecord[i] HomeRecord[i]); } else if(i { return new MLBrst(t.Abreviated_Short AwayRecord[i] null); } else if(i { return new MLBrst(t.Abreviated_Short null HomeRecord[i]); } else { return new MLBrst(t.Abreviated_Short null null); } }).AsEnumerable().ToList(); and your constructor to this: public MLBrst(string team MLBrst ar MLBrst hr) { Team = team; if (ar != null && hr != null) { Wins = ar.Wins + hr.Wins; Losses = ar.Losses + hr.Losses; Spread = (ar.Spread + hr.Spread) / (Wins + Losses); Total = (ar.Total + hr.Total) / (Wins + Losses); RS = ar.RS + hr.RS; RA = ar.RA + hr.RA; } else if(ar != null && hr == null) { Wins = ar.Wins; Losses = ar.Losses; Spread = ar.Spread / (Wins + Losses); Total = ar.Total / (Wins + Losses); RS = ar.RS; RA = ar.RA; } else if(ar == null && hr != null) { Wins = hr.Wins; Losses = hr.Losses; Spread = hr.Spread / (Wins + Losses); Total = hr.Total / (Wins + Losses); RS = hr.RS; RA = hr.RA; } else { Wins = 0; Losses = 0; Spread = 0; Total = 0; RS = 0; RA = 0; } GP = Wins + Losses; PD = RS - RA; }

Rich · Answer

Nice! Thanks for your help I really appreciate it.

Rich · Answer

Ok thanks to your help I've figured it out. My Away and Home records weren't actually returning some of the teams at all (not even null) they were absent due to other determining factors. So I solved that with the code below: // Get List of All Teams List TotalTeams = new List (); foreach (mlb_Team_Names item in Teams) { TotalTeams.Add(item.Abreviated_Short); } // List of Away Teams List AwayTeams = new List (); foreach (MLBrst item in AwayRecord) { AwayTeams.Add(item.Team); } // List of Home Teams List HomeTeams = new List (); foreach (MLBrst item in HomeRecord) { HomeTeams.Add(item.Team); } // Get the Teams index count int TeamsIndex = Teams.Count(); // Check to see if the teams indexes match. If not then add missing teams. if (TeamsIndex != AwayTeams.Count()) { List atMissing = TotalTeams.Except(AwayTeams).ToList(); foreach (string item in atMissing) { AwayRecord.Add(new MLBrst { Team = item Losses = 0 Spread = 0m Total = 0m }); } } if (TeamsIndex != HomeTeams.Count()) { List htMissing = TotalTeams.Except(HomeTeams).ToList(); foreach (string item in htMissing) { HomeRecord.Add(new MLBrst { Team = item Losses = 0 Spread = 0m Total = 0m }); } } The Except extension method was the main thing that helped. My question now is is there a more efficient or concise way to write the above code?

Rich · Answer

Vulpes I didn't realize that you could do that. That's a great tactic but am I wrong in assuming that that would return one or both records completely null depending on the if conditions? Let me provide an example below to better explain my situation. Teams: AwayRecord: HomeRecord: t1 t1 t1 t2 t2 t2 t3 none t3 t4 t4 none t5 t5 t5 to mlbStandings: t1 has AwayRecord and HomeRecord properties t2 has AwayRecord and HomeRecord properties t3 has null and HomeRecord properties t4 has AwayRecord and null properties t5 has AwayRecord and HomeRecord properties Sorry for any confusion.