C# - Failed to compare two elements in the array

Question

This is my code:

 var distinctDateValues = dt.AsEnumerable()
                   .Select(row => new
                   {
                       Date = DateTime.Parse(row.Field<string>("DAY"))
                   })
                   .Distinct()
                   .ToList();

 distinctDateValues.Sort(); // getting error on this line

Values in distinctDateValues are:

The error i am getting is "Failed to compare two elements in the array."

Can anybody suggest me as what i am doing wrong here. I want to sort the values in date column of distinctDateValues.

Solution 1

Needless to create anonymous type, in your case the result distinctDateValues is a list of anonymous type, not a list of DateTime, you should get the sorted list of DateTime like below with OrderBy:

var distinctDateValues = dt.AsEnumerable()
               .Select(row => row.Field<DateTime>("DAY"))
               .Distinct()
               .OrderBy(x => x)
               .ToList();

Also, you should use built-in method Field<DateTime> instead of using one more step with DateTime.Parse

Solution 2

Just guessing here... your distinctDateValues don't know how to compare themselves... You would need to implement IComparable or something...

Try this:

var distinctDateValues = dt.AsEnumerable()
               .Select(row => DateTime.Parse(row.Field<string>("DAY")))
               .Distinct()
               .ToList();

 distinctDateValues.Sort(); // should not get any errors here...

If you really want to create an anonymous type (e.g., you are only showing us a small part of your code), try this:

var distinctDateValues = dt.AsEnumerable()
               .Select(row => new
               {
                   Date = DateTime.Parse(row.Field<string>("DAY"))
               })    
               .Distinct()
               .OrderBy(d => d.Date) // do the sorting here with linq
               .ToList();