What's the best way to keep regex matches in Excel? - excel

Question

I'm working off of the excellent information provided in "How to use Regular Expressions (Regex) in Microsoft Excel both in-cell and loops", however I'm running into a wall trying to keep the matched expression, rather than the un-matched portion:
"2022-02-14T13:30:00.000Z" converts to "T13:30:00.000Z" instead of "2022-02-14", when the function is used in a spreadsheet. Listed below is the code which was taken from "How to use Regular Expressions (Regex) in Microsoft Excel both in-cell and loops". I though a negation of the strPattern2 would work, however I'm still having issues. Any help is greatly appreciated.
Function simpleCellRegex(Myrange As Range) As String
Dim regEx As New RegExp
Dim strPattern As String
Dim strPattern2 As String
Dim strInput As String
Dim strReplace As String
Dim strOutput As String
strPattern = "^T{0-9][0-9][:]{0-9][0-9][:]{0-9][0-9][0-9][Z]"
strPattern2 = "^(19|20)\d\d([- /.])(0[1-9]|1[012])\2(0[1-9]|[12][0-9]|3[01])"
If strPattern2 <> "" Then
strInput = Myrange.Value
strReplace = ""
With regEx
.Global = True
.MultiLine = True
.IgnoreCase = False
.Pattern = strPattern2
End With
If regEx.test(strInput) Then
simpleCellRegex = regEx.Replace(strInput, strReplace)
Else
simpleCellRegex = "Not matched"
End If
End If
End Function

Answer 1

Replace is very powerful, but you need to do two things:
Specify all the characters you want to drop, if your regexp is <myregexp>, then change it to ^.*?(<myregexp>).*$ assuming you only have one date occurrence in your string. The parentheses are called a 'capturing group' and you can refer to them later as part of your replacement pattern. The ^ at the beginning and the $ at the end ensure that you will only match one occurrence of your pattern even if Global=True. I noticed you were already using a capturing group as a back-reference - you need to add one to the back-reference number because we added a capturing group. Setting up the pattern this way, the entire string will participate in the match and we will use the capturing groups to preserve what we want to keep.
Change your strReplace="" to strReplace="$1", indicating you want to replace whatever was matched with the contents of capturing group #1.
Here is a screenprint from Excel using my RegexpReplace User Defined Function to process your example with my suggestions:
I had to fix up your time portion regexp because you used curly brackets three times where you meant square, and you left out the seconds part completely. Notice by adjusting where you start and end your capturing group parentheses you can keep or drop the T & Z at either end of the time string.
Also, if your program is being passed system timestamps from a reliable source then they are already well-formed and you don't need those long, long regular expressions to reject March 32. You can code both parts in one as
([-0-9/.]{10,10})T([0-9:.]{12,12})Z and when you want the date part use $1 and when you want the time part use $2.