How to get values from IGrouping
C#LinqSelectIgroupingC# Problem Overview
I have a question about IGrouping
and the Select()
method.
Let's say I've got an IEnumerable<IGrouping<int, smth>>
in this way:
var groups = list.GroupBy(x => x.ID);
where list
is a List<smth>
.
And now I need to pass values of each IGrouping
to another list in some way:
foreach (var v in structure)
{
v.ListOfSmth = groups.Select(...); // <- ???
}
Can anybody suggest how to get the values (List<smth>
) from an IGrouping<int, smth>
in such a context?
C# Solutions
Solution 1 - C#
Since IGrouping<TKey, TElement>
implements IEnumerable<TElement>
, you can use SelectMany
to put all the IEnumerables
back into one IEnumerable
all together:
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 that builds/runs: https://dotnetfiddle.net/DyuaaP
Video commentary of this solution: https://youtu.be/6BsU1n1KTdo
Solution 2 - C#
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.
Solution 3 - C#
More clarified version of above answers:
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;
}
}
Solution 4 - C#
From definition of IGrouping :
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
}
Solution 5 - C#
var groups = list.GroupBy(x => x.ID);
> Can anybody suggest how to get the values (List
"IGrouping
- iterate on the group or
- use group.ToList() to convert it to a List
foreach (IGrouping<int, smth> group in groups)
{
var thisIsYourGroupKey = group.Key;
List<smth> list = group.ToList(); // or use directly group.foreach
}
Solution 6 - C#
Simply do this:
// this will "split" the list into groups
var groups = list.GroupBy(x => x.ID);
// groups is a "collection of lists"
foreach (var sublist in groups)
{
// now the sublist is only a part of the original list
// to get which is the value of ID, you can use sublist.Key
}
You don't need Select().GroupBy(expr)
makes "a list of lists", kind of.
Solution 7 - C#
If you have an IGrouping<GroupItem, ListItem>
, and you want to access the items of type ListItem
of this group without utilizing a foreach
loop, it's very simple. The object of type IGrouping<GroupItem, ListItem>
is of type IEnumerable<ListItem>
as well, as it is defined as:
public interface IGrouping<out TKey, out TElement> : IEnumerable<TElement>, IEnumerable
So you can simply say:
foreach (IGrouping<GroupItem, ListItem> group in list.GroupBy(x => x.ID))
{
IEnumerable<ListItem> itemsInThisGroup = group;
// ...
}
If for some reason, it has to be a List<T>
instead of an IEnumerable<T>
, you can of course still call itemsInThisGroup.ToList()
. But usually it's better not to if you needn't.
Solution 8 - C#
Assume that you have MyPayments class like
public class Mypayment
{
public int year { get; set; }
public string month { get; set; }
public string price { get; set; }
public bool ispaid { get; set; }
}
and you have a list of MyPayments
public List<Mypayment> mypayments { get; set; }
and you want group the list by year. You can use linq like this:
List<List<Mypayment>> mypayments = (from IGrouping<int, Mypayment> item in yearGroup
let mypayments1 = (from _payment in UserProjects.mypayments
where _payment.year == item.Key
select _payment).ToList()
select mypayments1).ToList();