excel - Changing the date format to yyyy-mm-dd

Question

I've got a date column that contains dates in mixed format. For example:

A
21.03.1990
03/21/1990

So, basically there are two different formats in one column: dd.mm.yyyy and mm/dd/yyyy. I'm trying to write a VBA script to change format of all dates in the column to be yyyy-mm-dd. That's what I've got so far:

Sub changeFormat()

Dim rLastCell As Range
Dim cell As Range, i As Long
Dim LValue As String

i = 1

With ActiveWorkbook.Worksheets("Sheet1")
    Set rLastCell = .Range("A65536").End(xlUp)
    On Error Resume Next
    For Each cell In .Range("A1:A" & rLastCell.Row)
        LValue = Format(cell.Value, "yyyy-mm-dd")
        .Range("B" & i).Value = LValue
        i = i + 1
    Next cell
    On Error GoTo 0
End With

End Sub

I know that it's not elegant piece of code, but I'm beginner with VBA so please forgive me. The problem with that code is that it just rewrite unchanged A column into column B, when I change argument in Format function from yyyy-mm-dd to dd/mm/yyyy it works, but only for dates in format mm/dd/yyyy, and leaves dd.mm.yyyy untouched. I would appreciate any advice.

Answer 1

UPDATED: NEW ANSWER

Here is a solution that will do the job! The sub routine includes a function that does the replacement (the function itself is really useful!). Run the sub and all occurances in column A will be fixed.

Sub FixDates()

Dim cell As range
Dim lastRow As Long

lastRow = range("A" & Rows.count).End(xlUp).Row

For Each cell In range("A1:A" & lastRow)
    If InStr(cell.Value, ".") <> 0 Then
        cell.Value = RegexReplace(cell.Value, _
        "(d{2}).(d{2}).(d{4})", "$3-$2-$1")
    End If
    If InStr(cell.Value, "/") <> 0 Then
        cell.Value = RegexReplace(cell.Value, _
        "(d{2})/(d{2})/(d{4})", "$3-$1-$2")
    End If
    cell.NumberFormat = "yyyy-mm-d;@"
Next

End Sub 

Place this function in the same module:

Function RegexReplace(ByVal text As String, _
                      ByVal replace_what As String, _
                      ByVal replace_with As String) As String

Dim RE As Object
Set RE = CreateObject("vbscript.regexp")

RE.pattern = replace_what
RE.Global = True
RegexReplace = RE.Replace(text, replace_with)

End Function

How it works: I have a nifty RegexReplace function that allows you to do replace using regular expressions. The sub mearly loops through your A column and does a regex replace for those 2 cases you mentioned. The reason I use an Instr() first is to determain if it needs the replacement, and which kind. You could technically skip this but doing replace on cells that don't need it is really costly. At the end I format the cell to your custom date format regardless of what's inside for safe measure.

In case you aren't familiar with Regex (for ref: http://www.regular-expressions.info/), the expression I am using is:

• Each item in () are capture groups - aka, the stuff you want to mess with
• d stands for a number [0-9].
• {2} means 2 of, and {4} mean 4 of. I have been explicit here for safety.
• The before the . in the first replace is needed since "." has special meaning.
• In VBA regex, you refer to capture groups by using $ + no. of group. This is how I flip the order of the 3 items.