How to get values from IGrouping

Problem

I have a question about the Select() function and IGrouping.

Assume I have an IEnumerableIGroupingint, smth>> as follows:

var groups = list.GroupBy(x => x.ID);

List is a Listsmth>, where list is a Listsmth>.

Now I need to find a mechanism to transmit the values of each IGrouping to another list:

foreach (var v in structure)
{
    v.ListOfSmth = groups.Select(...); // <- ???
}

Is there a way to extract the values (Listsmth>) from an IGroupingint, smth> in such a c++ program?

Asked by Illia Ratkevych

Solution #1

Because IGroupingTKey, TElement> implements IEnumerableTElement>, you can use SelectMany to combine all of the IEnumerables into one:

List<smth> list = new List<smth>();
IEnumerable<IGrouping<int, smth>> groups = list.GroupBy(x => x.id);
IEnumerable<smth> smths = groups.SelectMany(group => group);
List<smth> newList = smths.ToList();

Here’s an example of a program that compiles and runs: https://dotnetfiddle.net/DyuaaP

https://youtu.be/6BsU1n1KTdo provides a video commentary on this solution.

Answered by Matt Smith

Solution #2

foreach (var v in structure) 
{     
    var group = groups.Single(g => g.Key == v. ??? );
    v.ListOfSmth = group.ToList();
}

First you need to select the desired group. Then you can use the ToList method of on the group. The IGrouping is a IEnumerable of the values.

Answered by Tim Cools

Solution #3

Versions of the answers above that have been clarified:

IEnumerable<IGrouping<int, ClassA>> groups = list.GroupBy(x => x.PropertyIntOfClassA);

foreach (var groupingByClassA in groups)
{
    int propertyIntOfClassA = groupingByClassA.Key;

    //iterating through values
    foreach (var classA in groupingByClassA)
    {
        int key = classA.PropertyIntOfClassA;
    }
}

Answered by Bronek

Solution #4

IGrouping is defined as follows:

IGrouping<out TKey, out TElement> : IEnumerable<TElement>, IEnumerable

you can just iterate through elements like this:

IEnumerable<IGrouping<int, smth>> groups = list.GroupBy(x => x.ID)
foreach(IEnumerable<smth> element in groups)
{
//do something
}

Answered by user1275513

Solution #5

var groups = list.GroupBy(x => x.ID);

Because “IGroupingint, smth> group” is an IEnumerable with a key, you have two options:

foreach (IGrouping<int, smth> group in groups)
{
   var thisIsYourGroupKey = group.Key; 
   List<smth> list = group.ToList();     // or use directly group.foreach
}

Answered by SA-

Post is based on https://stackoverflow.com/questions/8521025/how-to-get-values-from-igrouping