Unique Value Function in Excel - vba

Question

I created the following function using Excel 2010. It seem to work only when i use the function in the same sheet the array was created (sheet2) and if a value is typed in the function e.g.: =KeyExists(1443). I need to use this function in another sheet within the workbook and needs to be a cell reference. Stumped on why its not working.
Option Explicit
Function KeyExists(k)
Dim d As Object
Dim c As Variant
Dim i As Long
Dim lr As Long
Dim msg As String
Set d = CreateObject("Scripting.Dictionary")
lr = WorkSheets("Sheet2").Cells(Rows.Count, 1).End(xlUp).Row
c = Range("A2:A" & lr)
For i = 1 To UBound(c, 1)
d(c(i, 1)) = 1
Next i
If d.exists(k) Then
msg = "key exists"
Else
msg = "key does not exist"
End If KeyExists = msg
End Function
'parts of the code derived from:
'hiker95, 07/26/2012
'http://www.mrexcel.com/forum/showthread.php?649576-Extract-unique-values-from-one-column-using-VBA

Answer 1

Change it from Sheet2 to the active sheet:
lr = ActiveWorkbook.ActiveSheet.Cells(Rows.Count, 1).End(xlUp).Row

Answer 2

If the unique Keys are only in Sheet2 Column A2 and onward... You can create a dynamic named Range and reference it anywhere in the Workbook.
Say you have data:
Create a dynamic named range Keys with =OFFSET(Sheet2!$A$1,1,0,COUNTA(Sheet2!$A:$A)-1,1).
Then say you want to check for values in C4, use formula below:
=IF(ISNUMBER(IFERROR(MATCH(C4,Keys,0),"")),"key exists","key does not exists")
There is no need to use VBA for what you want to achieve your goal. e.g.

Answer 3

I agree with commenters regarding the Dictionary. In my opinion, it would be much easier to do without it. I also think other ways would be vastly quicker, depending on how much data you have.
Example:
Function KeyExists(k As Range) As String
Dim ws As Worksheet
Dim c As Range, i As Long
' Set ws to the worksheet to which k belongs.
' This avoids activeworksheet and also allows for
' qualified references to other sheets if necessary.
ws = k.Worksheet
Set c = ws.Range("A2:A" & ws.Cells(Rows.Count, 1).End(xlUp).Row)
On Error Resume Next
i = Application.WorksheetFunction.Match(k.Value, c, 0)
On Error GoTo 0
If i <> 0 Then
KeyExists = "Key exists"
Else
KeyExists = "Key does not exist"
End If
End Function
Using MATCH will most likely be a lot faster than adding every entry of data into a Dictionary.
A case where you might argue using Dictionary is marginally better, is if you want to make sure the value is unique. But even then, you'd have to use round-about logic to deal with the what-if of encountering duplicate keys and what to do at that point.
Your question does not really specifiy whether or not you need to perform this check or not, or what to do if duplicates are found, so it's hard to advise on it. In any case, if you opt for this method I would recommend creating a separate procedure that declares and builds the dictionary and run it on Worksheet_Open or something like that, leaving you to use a very short function for querying the existence of a key. This circumvents you having to build the dictionary every time the formula runs and will most likely be faster (and require more coding) than my solution.