c# and LINQ - convert IGrouping to List

Question

I have the following code written to find common objects in a list of objects

https://dotnetfiddle.net/gCgNBf

..............................

var query = setOfPersons
            .SelectMany(l => l.Select(l1 => l1))
            .GroupBy(p => p.Id)
            .Where(g => g.Count() == setOfPersons.Count);

After that, I need to convert "query" to a list of "Person" objects ( List ) to achieve something else.

I tried using "ToList()"... But it says:

" cannot convert IGrouping to a List ".

Can someone help me to fix it ?

Answer 1

Looking at your code it seems that what you are trying to achieve is to get the list of people that exist in each list. If so, you can use the following query:

var query = setOfPersons
    .SelectMany(l => l.Select(l1 => l1))
    .GroupBy(p => p.Id)
    .Where(g => g.Count() == setOfPersons.Count)
    .Select(x=>x.First())             // Select first person from the grouping - they all are identical
    .ToList();

Console.WriteLine("These people appears in all set:");

foreach (var a in query)
{
    Console.WriteLine("Id: {0} Name: {1}", a.Id, a.Name);
}

Here you select just a single item from each grouping, because they all are identical.