How to group by having lambda expression in C#?

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Select id from table person where per=123 group by a,b having count(*)=max(d)

Myentity.Person.where(x=>x.per=123).GroupBy(x=>new {x.a,x.b})

What I have tried:

How to lambda expression this query.

Posted 27-May-20 21:38pm

Member 14169626

Updated 27-May-20 23:11pm

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Maciej Los · Answer 1 · 2020-05-27T23:12:00

Solution 2

Try:

C#

var result = Myentity.Person
    .Where(x=>x.per==123)
    .GroupBy(x=>new {x.a, x.b})
    .Select(grp=> grp.OrderByDescending(x=> x.d).First())
    .ToList();

Posted 27-May-20 23:12pm

Maciej Los

Updated 28-May-20 20:39pm

v2

Comments

Richard MacCutchan 28-May-20 5:50am

5ed for a proper solution.

Maciej Los 28-May-20 5:54am

Thank you, Richard.

Member 14169626 28-May-20 6:21am

Thank you

Maciej Los 28-May-20 6:33am

You're very welcome.

George Swan 29-May-20 1:39am

Shouldn't the 'Where' clause be x=>x.per==123?

Maciej Los 29-May-20 1:58am

There is. At the beginning.

George Swan 29-May-20 2:02am

Haven't you used the assignment operator '=' instead of the '==' operator?

Maciej Los 29-May-20 2:37am

Good catch!
Corrected!
Thanks, George.

George Swan 29-May-20 5:10am

I think that the following 'Select' statement may be slightly quicker as there is no need to sort the collection.
Select(grp => grp.Where(p=>p.d==grp.Max(p=>p.d)))

Maciej Los 29-May-20 5:14am

I'd suggest to post this as a solution. It deserves for 5!

George Swan 29-May-20 5:24am

I couldn't take the credit for that as the original idea was yours, I just modified it slightly.

Maciej Los 29-May-20 5:49am

Yes, you can ;)

Richard MacCutchan · Answer 2 · 2020-05-27T22:54:00

Solution 1

Lambda expressions - C# Programming Guide | Microsoft Docs[^]

Posted 27-May-20 22:54pm

Richard MacCutchan

Comments

Maciej Los 28-May-20 5:11am

5ed!