Get the first record of a group in LINQ?
Solution 1
data
.GroupBy(
x => x.CardId,
(x, y) => new {
Key = x,
Value = y.OrderByDescending(z => z.DateTimeStamp).FirstOrDefault()
}
);
This will group all the elements by CardId
, then order the elements of each group by DateTimeStamp
(descending), then pare down each group to only contain the first element. Finally, it returns an enumerable of "groups" (with the scare quotes since they're actually an anonymous type instead of an IGrouping
) where each group has the one item you're seeking.
Solution 2
I find the query expression syntax easier to understand myself:
from x in data
group x by x.CarId into grp
select new {
CarId = x.CarId,
Record = (from x in grp orderby z.DateTimeStamp descending).FirstOrDefault()
};
RyBolt
SOreadytohelp Striving for better software, and hope to collaborate with others with similar goals. SOreadytohelp
Updated on June 04, 2022Comments
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RyBolt almost 2 years
Summary: How to get top 1 element in ordered groups of data
I am trying to group by a CarId field , and then within each group, I want to sort on a DateTimeStamp field descending. The desired data would be for each Car give me the latest DateTimeStamp and only that 1 in the group.
I can get to this point, but having problems taking the top 1 off of the group and ordering the group by DateTimeStamp desc.
Here is what I have after the first group operation:
group 1 ------------------------ CarId DateTimeStamp 1 1/1/2010 1 1/3/2010 1 3/4/2010 group 2 ------------------------ CarId DateTimeStamp 2 10/1/2009 2 1/3/2010 2 9/4/2010
what I would desire only the top 1 in an ordered group
group 1 ------------------------ CarId DateTimeStamp 1 3/4/2010 group 2 ------------------------ CarId DateTimeStamp 2 9/4/2010
Brickwall: Where I get stopped, is needing the CarId and DateTimeStamp in the group by clause, in order to later sort by the DateTimeStamp. Maybe the sorting of the date should be done in a separate function, not sure.
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RyBolt over 13 yearsThat did it! I did get an exception and had to use FirstOrDefault() instead of First(). Thanks!
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Gone Coding almost 13 years+1: Perfect. Just what I needed (a version of grouping and first record I can actually follow :)
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Shaiju T over 8 yearsthank you, i was searching for this, i searched
sql group by last record
but didn't find solutionlinq group by last record
helped to come here, only need is ,i have to make it 'typed' forViewModel
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Si8 almost 7 yearsCan I concatenate two columns in the orderbydescending? Like
z.Field<string>("Date") + z.Field<string>("Time")
? Since they are string and separate columns, how can I achieve that? How can I select multiple column beside theCardId
? -
Kirk Woll almost 7 years@Si8, you should really ask a separate question, but what you want is
.OrderByDescending(...).ThenByDescending(...)
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Si8 almost 7 yearsYou are absolutely right and i did. I forgot to mention it here. Thanks. stackoverflow.com/questions/44764687/…