Using LINQ to merge a list of objects
I have two lists of objects, using Linq I would like to merge them, but where the two lists contain objects with the same key, I only want the one with the greatest LastUpdated Value.
I thought that I could somehow get a list grouping by key a with max(LastUpdated) then join back to the list joining on key and LastUpdated, but there must be a mor开发者_如何学Goe efficient way...
List<MyObject> lstListA = new List<MyObject>;
List<MyObject> lstListB = new List<MyObject>;
public class MyObject
{
public string Key {get;set;}
public string Value {get;set;}
public DateTime LastUpdated {get;set;}
}
One option, using DistinctBy
from MoreLINQ:
var query = lstListA.Concat(lstListB)
.OrderByDescending(x => x.LastUpdated)
.DistinctBy(x => x.Key);
Classic pick-a-winner.
IEnumerable<MyObject> query = lstListA
.Concat(lstListB)
.GroupBy(x => x.Key)
//now work with each group to pick a winner
.Select(g => g.OrderByDescending(x => x.LastUpdated).First())
A bit comvoluted, but this seems to work as well:
var mergedItems = lstListA.Concat(lstListB);
mergedItems =
(from item in mergedItems
group item by item.Key into grp
let sameKey = mergedItems.Where(obj => obj.Key == grp.Key)
select sameKey.Where(obj => obj.LastUpdated == grp.Max(obj2 => obj2.LastUpdated)).Single()
).ToList();
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