Excel trigram (3 ngram) comparison function

excel_trigram_comparison.vb

Function preg_replace(text, strPattern As String, strReplace As String)
    Dim txt As String: txt = text
   
    Set regEx = CreateObject("VBScript.RegExp")
    
    With regEx
        .Global = True
        .MultiLine = False
        .IgnoreCase = False
        .Pattern = strPattern
    End With
    If Len(strPattern) > 0 And regEx.Test(txt) Then
        txt = regEx.Replace(txt, strReplace)
    End If
    preg_replace = txt
End Function

Function TRIGRAM(str)
    str__ = "__" & str & "__"
    
    Dim trigrams As String: trigrams = ""
    
    For i = 1 To Len(str) + 2
        trigrams = trigrams & " " & Mid(str__, i, 3)
    Next i
    
    TRIGRAM = trigrams
End Function

Function TRIGRAM_COMPARE(str1_ As String, str2_ As String)
    str1 = TRIGRAM(preg_replace(LCase(str1_), "[(). ,/\\+*\-""']+", ""))
    str2 = TRIGRAM(preg_replace(LCase(str2_), "[(). ,/\\+*\-""']+", ""))
    
    str1split = Split(Trim(str1), " ")

    str2trunc = str2
    
    For i = 0 To UBound(str1split, 1)
        str2trunc = Replace(str2trunc, " " & str1split(i), "", 1, 1)
    Next
    
    trigramsCount = (Len(str2) / 4)
    TRIGRAM_COMPARE = (Len(str2trunc) / 4) & "/" & (trigramsCount - 2)
End Function