Question

Is there a clever way using VBA or a formula to find “k” and “m” variables in a kx+m string?

There are several scenarios for how the kx+m string can look, e.g.:

312*x+12
12+x*2
-4-x

and so on. I’m pretty sure I can solve this by writing very complicating formulas in Excel, but I’m thinking maybe someone has already solved this and similar problems. Here is my best shot so far, but it doesn’t handle all situations yet (like when there are two minuses in the kx+m string:

=TRIM(IF(NOT(ISERROR(SEARCH("~+";F5)));
IF(SEARCH("~+";F5)>SEARCH("~*";F5);RIGHT(F5;LEN(F5)-SEARCH("~+";F5));LEFT(F5;SEARCH("~+";F5)-1));
IF(NOT(ISERROR(SEARCH("~-";F5)));
IF(SEARCH("~-";F5)>SEARCH("~*";F5);RIGHT(F5;LEN(F5)-SEARCH("~-";F5)+1);LEFT(F5;SEARCH("~*";F5)-1));"")))

Answer 1

I’m sure this will help you 🙂

Put this function in a Module:

Function FindKXPlusM(ByVal str As String) As String
    Dim K As String, M As String
    Dim regex As Object, matches As Object, sm As Object

    '' remove unwanted spaces from input string (if any)
    str = Replace(str, " ", "")

    '' create an instance of RegEx object.
    '' I'm using late binding here, but you can use early binding too.
    Set regex = CreateObject("VBScript.RegExp")
    regex.IgnoreCase = True
    regex.Global = True

    '' test for kx+m or xk+m types
    regex.Pattern = "^(-?\d*)\*?x([\+-]?\d+)?$|^x\*(-?\d+)([\+-]?\d+)?$"
    Set matches = regex.Execute(str)
    If matches.Count >= 1 Then
        Set sm = matches(0).SubMatches
        K = sm(0)
        M = sm(1)
        If K = "" Then K = sm(2)
        If M = "" Then M = sm(3)
        If K = "-" Or K = "+" Or K = "" Then K = K & "1"
        If M = "" Then M = "0"
    Else
        '' test for m+kx or m+xk types
        regex.Pattern = "^(-?\d+)[\+-]x\*([\+-]?\d+)$|^(-?\d+)([\+-]\d*)\*?x$"
        Set matches = regex.Execute(str)
        If matches.Count >= 1 Then
            Set sm = matches(0).SubMatches
            M = sm(0)
            K = sm(1)
            If M = "" Then M = sm(2)
            If K = "" Then K = sm(3)
            If K = "-" Or K = "+" Or K = "" Then K = K & "1"
            If M = "" Then M = "0"
        End If
    End If
    K = Replace(K, "+", "")
    M = Replace(M, "+", "")

    '' the values found are in K & M.
    '' I output here in this format only for showing sample.
    FindKXPlusM = " K = " & K & "         M = " & M
End Function

Then you can either call it from a Macro
e.g. like this:

Sub Test()
    Debug.Print FindKXPlusM("x*312+12")
End Sub

Or use it like a formula.
e.g. by putting this in a cell:

=FindKXPlusM(B1)

I like the second way (less work :P)

I tested it with various values and here’s a screenshot of what I get:

Hope this helps 🙂