Using LINQ to filter records in an object-CodePudding

I have a deserialized Json object that I am trying to filter before processing. The data looks like this...

Company     Division    LastModDate   Lot's of other columns/objects
123         1           7/1/2021
123         1           8/1/2022
123         2           8/1/2022

How can I get all the information in the original object and get rid of records that are not the latest for each Company/Division group?

I tried this...

var filtered = origObject.GroupBy(g=> new {g.Company,g.Division})

I don't know where to go next.

If I were doing this in SQL then I would be using row_number and just taking the 1 for example.

CodePudding user response：

You could try something like

var filtered = origObject
    .GroupBy(x => new {g.Company,g.Division})
    .Select(g => g.OrderByDescending(x => x.LastModDate).First());

This will select one latest object from each group.

Edit: I'm not sure without a compiler at hand if this will group correctly - your grouping key is an anonymous object, I don't remember if they have any equality comparer other than by reference. You could try using a record instead, records have equality by value of all their properties - .GroupBy(g => (g.Company,g.Division)). Or just group by a string key such as $"{g.Company},{g.Division}",

CodePudding user response：

A much more efficient way of doing this is as follows:

var filtered = origObject
    .OrderByDescending(w => w.LastModDate)
    .DistinctBy(w => (w.Company, w.Division));

This avoids the heavy array allocation and copying of GroupBy, especially since you only care about one item from its result.