Regular expression for an Excel cell with R1C1 notation - regex

Question

I need some code to test if a cell contains a formula with a reference to another cell.
I found the answer Find all used references in Excel formula but the solution matches wrongly also formula with references to table columns as :
=SearchValInCol2(Tabella1[articolo];[#articolo];Tabella1[b])
Then, I wrote the following VBA code using the Like operator, but surely a solution with a regular expression would be more solid (I think the following code won't work in many scenarios).
Private Function TestIfCellContainsAFormula(cellToTest As Variant) As Boolean
Dim result As Object
Dim r As Range
Dim testExpression As String
Dim objRegEx As Object
Set r = cellToTest ' INPUT THE CELL HERE , e.g. RANGE("A1")
Set objRegEx = CreateObject("VBScript.RegExp")
objRegEx.IgnoreCase = True
objRegEx.Global = True
objRegEx.Pattern = """.*?""" ' remove expressions
testExpression = CStr(r.FormulaR1C1)
' search for pattern "=R[-3]C+4"
If testExpression Like "*R[[]*[]]*C*" Then
TestIfCellContainsAFormula2 = True
Exit Function
End If
' search for pattern "=RC[2]"
If testExpression Like "*R*C[[]*[]]*" Then
'If InStr(1, testExpression, "C[", vbTextCompare) <> 0 Then
TestIfCellContainsAFormula2 = True
Exit Function
End If
TestIfCellContainsAFormula2 = False
End Function

Answer 1

Option 1
To match R1C1 style references you can use this regex:
R(\[-?\d+\])C(\[-?\d+\])|R(\[-?\d+\])C|RC(\[-?\d+\])
See the railroad diagram for a visual explanation:
At the core is the 'offset' which is -?\d+ which is optional - followed by a digit or more. This sequence goes in the brackets ([]) to give \[-?\d+\]. Then the regex allows combinations of:
R[offset]C[offset]
R[offset]C or (|)
RC[offset] or (|)
Option 2
The regex above won't match R, C, or RC. It will match R[0], C[0], R[0]C, RC[0], and R[0]C[0] which are kind of equivalent. To eliminate those matches you might use this regex:
R(\[-?[1-9][0-9]*\])C(\[-?[1-9][0-9]*\])|R(\[-?[1-9][0-9]*\])C|RC(\[-?[1-9][0-9]*\])
Which is this:
But it seems entering R[0], C[0] and R[0]C[0] in my Excel (v2013) turns them into R, C and RC anyways - so you can avoid the additional complexity if this is not a concern.
Option 3
If you want to allow R, C and RC you can use a simpler regex:
R(\[-?\d+\])?C(\[-?\d+\])?
VBA test code
This uses Option 1.
Option Explicit
Sub Test()
Dim varTests As Variant
Dim varTest As Variant
Dim varMatches As Variant
Dim varMatch As Variant
varTests = Array("RC", _
"R[1]C", _
"RC[1]", _
"R[1]C[1]", _
"R[-1]C", _
"RC[-1]", _
"R[-1]C[-1]", _
"=SUM(A1:B2)", _
"RC[1]+R[-1]C+R[2]C[-99]", _
"R[-1]C-R[1]C[-44]-RC[999]+R[0]C[0]", _
"SearchValInCol2(Tabella1[articolo];[#articolo];Tabella1[b])")
For Each varTest In varTests
varMatches = FormulaContainsR1C1Reference(CStr(varTest))
Debug.Print "Input: " & CStr(varTest)
Debug.Print VBA.String(Len(CStr(varTest)) + 7, "-")
If IsEmpty(varMatches) Then
Debug.Print "No matches"
Else
Debug.Print UBound(varMatches) & " matches"
For Each varMatch In varMatches
Debug.Print varMatch
Next varMatch
End If
Debug.Print vbCrLf
Next varTest
End Sub
Function FormulaContainsR1C1Reference(ByVal strFormula As String) As Variant
Dim objRegex As Object
Dim strPattern As String
Dim objMatches As Object
Dim varMatches As Variant
Dim lngCounter As Long
Set objRegex = CreateObject("VBScript.RegExp")
With objRegex
' setup regex
.Global = True
.IgnoreCase = False
.Pattern = "R(\[-?\d+\])C(\[-?\d+\])|R(\[-?\d+\])C|RC(\[-?\d+\])"
' get matches
Set objMatches = .Execute(strFormula)
' iterate matches
If objMatches.Count > 0 Then
ReDim varMatches(1 To objMatches.Count)
For lngCounter = 1 To objMatches.Count
varMatches(lngCounter) = objMatches.Item(lngCounter - 1)
Next lngCounter
Else
varMatches = Empty
End If
End With
FormulaContainsR1C1Reference = varMatches
End Function
A1 style references
I posted a regex here for A1 style references:
^(?:[A-Z]|[A-Z][A-Z]|[A-X][A-F][A-D])(?:[1-9]|[1-9][0-9]|[1-9][0-9][0-9]|[1-9][0-9][0-9][0-9]|[1-9][0-9][0-9][0-9][0-9]|[1-9][0-9][0-9][0-9][0-9][0-9]|10[0-3][0-9][0-9][0-9][0-9]|104[0-7][0-9][0-9][0-9]|1048[0-4][0-9][0-9]|10485[0-6][0-9]|104857[0-6])$