Question

I’m currently writing a library where I wish to allow the user to be able to specify spreadsheet cell(s) under four possible alternatives:

1. A single cell: "A1";
2. Multiple contiguous cells: "A1:B10"
3. Multiple separate cells: "A1,B6,I60,AA2"
4. A mix of 2 and 3: "B2:B12,C13:C18,D4,E11000"

Then, to validate whether the input respects these formats, I intended to use a regular expression to match against. I have consulted this article on Wikipedia:
Regular Expression (Wikipedia)

And I also found this related SO question:
regex matching alpha character followed by 4 alphanumerics.

Based on the information provided within the above-linked articles, I would try with this Regex:

Default Readonly Property Cells(ByVal cellsAddresses As String) As ReadOnlyDictionary(Of String, ICell)
    Get
        Dim validAddresses As Regex = New Regex("A-Za-z0-9:,A-Za-z0-9")

        If (Not validAddresses.IsMatch(cellsAddresses)) then _
            Throw New FormatException("cellsAddresses")

        // Proceed with getting the cells from the Interop here...  
    End Get
End Property

Questions

1. Is my regular expression correct? If not, please help me understand what expression I could use.

2. What exception is more likely to be the more meaningful between a FormatException and an InvalidExpressionException? I hesitate here, since it is related to the format under which the property expect the cells to be input, aside, I’m using an (regular) expression to match against.

Thank you kindly for your help and support! =)

Answer 1

Assuming that the column for the spreadsheet is any 1- or 2-letter value and the row is any positive number, a more complex but tighter answer still would be:

^[A-Z]{1,2}[1-9]\d*(:[A-Z]{1,2}[1-9]\d*)?(,[A-Z]{1,2}[1-9]\d*(:[A-Z]{1,2}[1-9]\d*)?)*$

“[A-Z]{1,2}[1-9]\d*” is the expression for a single cell reference. If you replace “[A-Z]{1,2}[1-9]\d*” in the above with then the complex expression becomes

^<cell>(:<cell>)?(,<cell>(:<cell>*)?)*$

which more clearly shows that it is a cell or a range followed by one or more “cell or range” entries with commas in between.

The row and column indicators could be further refined to give a tighter still, yet more complex expression. I suspect that the above could be simplified with look-ahead or look-behind assertions, but I admit those are not (yet) my strong suit.