Replacing nested loop with Linq

Question

In the query below I do calculate the combined value of all football teams within league 1. The solution I've came up with, though it works, seems rather bulky.

I would like to find a better approach i.e. a one lined linq query like so:

footballteams.Where(x => x.League == 1).Sum(x => x.Networth);

My current code:

List<IGrouping<int, FootballTeam>> footballTeams = context.FootballTeam
    .GetQueryable()
    .GroupBy(x => x.TeamName)
    .ToList();

var prem = footballTeams.Where(x => x.League == 1).ToList();
var totalWealth = 0;

foreach (var team in prem)
{
    foreach(var singleteam in team)
    {
         totalWealth = totalWealth + singleteam.networth;
    }
}

Why group and then ungroup to get the sum of the networth? Wouldn't it make more sense to get the teams as a List<FootballTeam>, then from this list you can group or you can sum, whichever you like? Also, how can you run .Where(x => x.League == 1) on an IGrouping? Those objects don't have a .League property. — ErikE
– ErikE, Commented Jun 5, 2018 at 21:57

Erik Philips · Accepted Answer · 2018-06-05 21:47:29Z

11

Use SelectMany then Sum.

var totalWealth = footballTeams.Where(x => x.League == 1)
                               .SelectMany(x => x.Select(e => e.networth))
                               .Sum();

SelectMany() Exceprt:

Projects each element of a sequence to an IEnumerable and flattens the resulting sequences into one sequence.

edited Jun 5, 2018 at 21:47

Erik Philips

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answered Jun 5, 2018 at 21:39

Ousmane D.

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Comments

Camilo Terevinto · Accepted Answer · 2018-06-05 21:41:28Z

4

You can do it all in a single statement:

var totalWorth = context.FootballTeam
    .GetQueryable()
    .Where(x => x.League == 1)
    .GroupBy(x => x.TeamName)
    .Sum(x => x.Sum(y => y.NetWorth));

You also skip the enumeration performed by the two ToList() calls with this.

answered Jun 5, 2018 at 21:41

Camilo Terevinto

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Comments

Tobias Brohl · Accepted Answer · 2018-06-05 21:53:07Z

4

totalWealth = footballTeams
    .Where(x => x.League == 1)
    .Select(
        x => x.Select(
            y => y.networth
        ).Sum()
    )
    .Sum();

If you want you can make it one line, but you will notice that readability is crucial for productive coding.

edited Jun 5, 2018 at 21:53

answered Jun 5, 2018 at 21:37

Tobias Brohl

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4 Comments

CodeNotFound Over a year ago

this will not compile. Due to the second Select. TO make it compile the first Select should be SelectMany

Ousmane D. Over a year ago

@CodeNotFound I think they meant to do .Select(x => x.Select(y => y.networth).Sum()).Sum();. With the current example, seems like there is a typo y.networth.Sum() from the author.

Ousmane D. Over a year ago

@CodeNotFound with the edit, it should now work. Also, note that SelectMany is only required if you want to collapse nested sequences, the inner Select in the answer returns a scalar value so SelectMany is not required here. But yes one could also do it with SelectMany as in my answer :).

CodeNotFound Over a year ago

great . You're right. SelectManay not needed with this version :-)

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