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

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.

Answer 2

You don't really need VBA for this. This one-liner worksheet formula will do the trick:
=IF(ISERROR(FIND(".",A1)),IF(ISERROR(FIND("/",A1)),"invalid format",
DATE(RIGHT(A1,4),LEFT(A1,2),MID(A1,4,2))),
DATE(RIGHT(A1,4),MID(A1,4,2),LEFT(A1,2)))
This assumes the day and month are always given as two-digit numbers (e.g. always 03 and never just 3) and the year has four digits (i.e. "restricted" to years 1000-9999). But if this is not the case for you, then the formula can easily be adjusted to suit your purpose.

Answer 3

See if this does what you want. You may have to tailor it a bit for your own application.
Hope this helps!
Sub convertDates()
Dim rRng As Range
Dim rCell As Range
Dim sDest As String
Dim sYear, sMonth, sDay, aDate
'Range where the dates are stored, excluding header
Set rRng = Sheet1.Range("A2:A11")
'Column name of destination
sDest = "B"
'You could also use the following, and just select the range.
'Set rRng = Application.selection
For Each rCell In rRng.Cells
sYear = 99999
If InStr(rCell.Value, ".") > 0 Then
aDate = Split(rCell.Value, ".")
If UBound(aDate) = 2 Then
sDay = aDate(0)
sMonth = aDate(1)
sYear = aDate(2)
End If
ElseIf InStr(rCell.Value, "/") > 0 Then
aDate = Split(rCell.Value, "/")
If UBound(aDate) = 2 Then
sDay = aDate(1)
sMonth = aDate(0)
sYear = aDate(2)
End If
End If
With rCell.Range(sDest & "1")
If sYear <> 99999 Then
On Error Resume Next
.Value = "'" & Format(CDate(sMonth & "/" & sDay & "/" & sYear), "YYYY-MM-DD")
'If it can't convert the date, just put the original value in the dest
'cell. You can tailor this to your own preference.
If Err.Number <> 0 Then .Value = rCell.Value
On Error GoTo 0
Else
.Value = rCell.Value
End If
End With
Next
End Sub

Answer 4

#Jean-François Corbett has a formula solution that works but that might be shortened by more than half by foregoing the error message (on the basis that #VALUE! is as informative) and another IF, both DATEs, applying IFERROR rather than ISERROR, and SUBSTITUTE in place of one LEFT, MID, RIGHT set:
=IFERROR(1*(MID(A1,4,3)&LEFT(A1,3)&RIGHT(A1,4)),1*SUBSTITUTE(A1,".","/"))
This applies the interpretation mentioned by #Issun in the comment to the OP and assumes the output will be to cells formatted yyyy-mm-dd.
May be written with a subroutine like so:
Sub Macro1()
Range("B1:B10").Formula = "=IFERROR(1*(MID(A1,4,3)&LEFT(A1,3)&RIGHT(A1,4)),1*SUBSTITUTE(A1,""."",""/""))"
End Sub

Answer 5

Here is a simple solution to this:
Sub ChangeFormat1()
Dim ws as Worksheet
Set ws = Thisworkbook.Sheets("Sheet1")
LR = ws.cells(rows.count,1).End(Xlup).Row
with ws
For I = 1 to LR
.cells(I,2).value = .cells(I,1).value
Next
End with
ws.range("B1:B" & LR).numberformat = "yyyy-mm-dd"
End Sub

Answer 6

Month(Date) & "-" & Day(Date) & "-" & Year(Date)