Groupby multiple date properties by month and year in LINQ

Question

I need to group by multiple properties by month and year in C# LINQ

This is my code:

public class Class1
{
    public Nulla         


        

Answer 1

You need to collect all the dates using SelectMany (in this particular case filter out the null values) and then do the typical GroupBy / Count projection:

var result = listGoogleTimezone
    .SelectMany(x => new[] { x.dt1, x.dt2 }.Where(dt => dt != null).Select(dt => dt.Value))
    .GroupBy(dt => new { dt.Month, dt.Year })
    .OrderBy(g => g.Key.Year).ThenBy(g => g.Key.Month) // optional
    .Select(g => new
    {
        g.Key.Month,
        g.Key.Year,
        Count = g.Count()
    }).ToList();

Answer 2

If you have MoreLinq referenced you can use make Ivan's answer cleaner by using CountBy:

var result = listGoogleTimezone
    .SelectMany(x => new[] { x.dt1, x.dt2 }
        .Where(dt => dt != null)
        .Select(dt => dt.Value))
    .CountBy(x => new { Year = x.Year, Month = x.Month });

This will can you an IEnumerable<KeyValuePair<TKey, int>> where the TKey is an anonymous type with Year and Month and the int is the count.