Read all unique values from cells in a range and create a comma separated string from them? - vb.net

Question

I have written the following function to read all unique values from cells in a range and create a comma separated string from them? Is there a better, simpler way to do this?
Private Sub CsvUniqueValues(r As Excel.Range)
Dim c As Excel.Range
Dim s As String = ""
For Each c In r.Cells
If ExcelApp.WorksheetFunction.CountIf(r, c.Value) = 1 Then
s = s & ","
End If
Next
If s.Length > 0 Then
s = s.Substring(0, s.Length - 1)
End If
End Sub

Answer 1

You could use LINQ to get a list of only the unique values, like this:
Dim uniqueValues As IEnumerable = r.Cells.Where(Function(x) ExcelApp.WorksheetFunction.CountIf(r, x.Value) = 1))
Then, you could use LINQ to convert all of those unique values to strings:
Dim uniqueStrings As IEnumerable(Of String) = uniqueValues.Select(Of String)(Function(x) x.ToString())
Then you can use LINQ to convert the resulting list to an array:
Dim uniqueArray() As String = uniqueStrings.ToArray()
Then, you could use the String.Join method to combine them into a single CSV string:
Dim csv As String = String.Join(",", uniqueArray)
You could, of course, do all of this in a single command, like this:
Dim csv As String = String.Join(",",
r.Cells.Where(Function(x) ExcelApp.WorksheetFunction.CountIf(r, x.Value) = 1))
.Select(Of String)(Function(x) x.ToString())
.ToArray())
The question, though, is whether or not you would call that "easier". LINQ is useful because it makes code easier to to read and write, but when it's taken too far, it can become less readable, thereby defeating the purpose of using it. At the very least, to make your code more clear, I would move the first part into a named function so it's more self-documenting:
Public Function GetUniqueCellValuesAsString(r As Excel.Range) As IEnumerable(Of String)
Return r.Cells.Where(
Function(x) ExcelApp.WorksheetFunction.CountIf(r, x.Value) = 1))
.Select(Of String)(Function(x) x.ToString())
End Function
Then you could just build the CSV string like this:
Dim csv As String = String.Join(",", GetUniqueCellValuesAsString(r).ToArray())

Answer 2

I would make use of the collection object. Since collections can only contain unique values, trying to add all of your input data to a collection will result in an array of unique values. The following modification lets CsvUniqueValues return a comma separated string from the values in any given range.
'Test function and return result in MsgBox
Sub ReturnUnique()
MsgBox CsvUniqueValues(Selection)
End Sub
'Function will return csv-string from input range
Function CsvUniqueValues(r As Range) As String
Dim Cell As Range
Dim i As Integer
Dim DistCol As New Collection
Dim s As String
'Add all distinct values to collection
On Error Resume Next
For Each Cell In r
DistCol.Add Cell.Value, Cell.Value
Next Cell
On Error GoTo 0
'Write collection to comma seperated list
For i = 1 To DistCol.Count
s = s & DistCol.Item(i) & "; "
Next i
s = Left(s, Len(s) - 2)
CsvUniqueValues = s
End Function