C#•3w ago

✅ Looping through collections with key value pairs

Hello guys, consider the following code:

C#
// percentileQuery is an IEnumerable<IGrouping<int, Country>>
var percentileQuery =
    from country in countries
    let percentile = (int)country.Population / 1_000
    group country by percentile into countryGroup
    where countryGroup.Key >= 20
    orderby countryGroup.Key
    select countryGroup;

// grouping is an IGrouping<int, Country>
foreach (var grouping in percentileQuery)
{
    Console.WriteLine(grouping.Key);
    foreach (var country in grouping)
    {
        Console.WriteLine(country.Name + ":" + country.Population);
    }
}

C#
// percentileQuery is an IEnumerable<IGrouping<int, Country>>
var percentileQuery =
    from country in countries
    let percentile = (int)country.Population / 1_000
    group country by percentile into countryGroup
    where countryGroup.Key >= 20
    orderby countryGroup.Key
    select countryGroup;

// grouping is an IGrouping<int, Country>
foreach (var grouping in percentileQuery)
{
    Console.WriteLine(grouping.Key);
    foreach (var country in grouping)
    {
        Console.WriteLine(country.Name + ":" + country.Population);
    }
}

I'm a bit confused about how grouping is used in the loops. The thing is I first tried to compare it with how we loop for a dictionary but in a dictionary, we would use grouping.Value in the inner loop but here, we used grouping in both loops. What's happening here please, how does grouping know which one is an int or which one is the collection.

11 Replies

canton7•3w ago

https://learn.microsoft.com/en-us/dotnet/api/system.linq.igrouping-2?view=net-9.0

IGrouping Interface (System.Linq)

Represents a collection of objects that have a common key.

Sehra•3w ago

IGrouping = Key + IEnumerable

canton7•3w ago

IGrouping inherits from IEnumerable but adds a Key property (it's not an object with a Key property and another property which is the IEnumerable)

We used grouping in both loops

Not really? In the first loop you're looping over percentileQuery, and calling each element grouping. In the second loop you're looping over grouping and calling each element country

MODiX•3w ago

Angius

REPL Result: Success

var u = new Unga<int>("hello") { 1, 2, 3, 76, 9 };

foreach (var x in u)
{
    Console.WriteLine($"{u.Bunga}: {x}");
}

public class Unga<T>(string bunga) : List<T>
{
    public string Bunga { get; set; } = bunga;
}

var u = new Unga<int>("hello") { 1, 2, 3, 76, 9 };

foreach (var x in u)
{
    Console.WriteLine($"{u.Bunga}: {x}");
}

public class Unga<T>(string bunga) : List<T>
{
    public string Bunga { get; set; } = bunga;
}

Console Output

hello: 1
hello: 2
hello: 3
hello: 76
hello: 9

hello: 1
hello: 2
hello: 3
hello: 76
hello: 9

Compile: 606.226ms | Execution: 69.156ms | React with ❌ to remove this embed.

Angius•3w ago

Similar example

FakerOP•3w ago

Yeah I see, so IGrouping<> is just an IEnumerable kind of? Just that each element in it has a key property?

Angius•3w ago

No, the grouping itself has a key property Just like my Unga is a List<T> but it also has a Bunga property

FakerOP•3w ago

ahhh yeah I see, that's why it's not possible to say something like x.Bunga but rather u.Bunga?

Angius•3w ago

Yeah, because x here is an int And int does not have a property called Bunga

FakerOP•3w ago

Yeahh I see I think it's clearer now will come back if I have other doubts but should be good for now, thanks guys !!

Angius•3w ago

:Ok:

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✅ Looping through collections with key value pairs

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