Question

How can I get a new distinct list from an existing list using LINQ? This is what I have so far and it is not distinct but does give me a new list.

Dim tmpQryColumn = (From a In _allAudits 
                    Select New CheckBoxListItem 
                    With {.Id = a.AuditColumn, .Name = a.AuditColumn} 
                    ).Distinct()
_columnList = New List(Of CheckBoxListItem)(tmpQryColumn)

Answer 1

I suspect the problem is that CheckboxListItem doesn’t override Equals/GetHashCode so any two instances are effectively distinct. Try:

Dim columns = (From a In _allAudits
               Select a.AuditColumn).Distinct()

_columnList = (From column in columns
               Select New CheckBoxListItem 
               With {.Id = column, .Name = column} 
               ).ToList()

I’m sure there’s a simpler way of writing it in VB, but I’m not familiar enough with the syntax to write it. The C# version would be:

_columnList = _allAudits.Select(x => x.AuditColumn)
                        .Distinct()
                        .Select(x => new CheckboxListItem { Id = x, Name = x })
                        .ToList();