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c#linqumbraco

Distinct value from collection by grouping and date

I have a list of Umbraco nodes with properties 'level', 'section', 'theme' and 'date', with the first three being strings, the last being a DateTime.

I need my list filtered so that each entry is unique based on a composite of 'level', 'section' and 'them'. however were duplicates are found, the node selected to remain in the list should be the node with the earliest date.

I've being trying to figure this out using LINQ and Lambdas but have finally hit a wall after a few hours.

Example

pre-filtering

level    section    theme    date
a        b          c        01/02/2003
d        b          c        01/04/2003
a        b          c        23/02/2015
d        b          c        12/12/2003
d        b          c        28/10/2003

post-filtering

level    section    theme    date
a        b          c        01/02/2003
d        b          c        01/04/2003

Group by level, section and theme. Where there is more than one entry, select the entry with the earliest date.

Probably pretty simple but I'm new to C#/LINQ. Any help appreciated.

Solution

  • This should be what you are looking for:

    var ans1 = from s in src
           group s by new { s.level, s.section, s.theme } into sg
           select new { sg.Key.level, sg.Key.section, sg.Key.theme, date = sg.Min(s => s.date) };

    GroupBy is often easier to understand in query comprehension, but if you prefer lambda syntax

    var ans2 = src.GroupBy(s => new { s.level, s.section, s.theme }, (skey, sg) => new { skey.level, skey.section, skey.theme, date = sg.Min(s => s.date) });