VBA - Recognize typos in email domain - vba

Question

I'm working on a VBA script that is to work through an extensive list of email addresses and flag the ones that are suspected of being wrong.
I'd like to refine the routine by adding a function that would spot typos in common domain names such as gmail, hotmail, msn, skynet, etc. I'll have a list of these common display names in an array.
The string function would see if the inputted string looks similar but is not the same as an element in the array, and return true as boolean if it is the case.
Idea is to spot erroneous entries such as: homtail, mns, slynet, hotmal, yahooo, etc.
Not looking for a script per se, looking for inspiration of how to tackle this problem...

Answer 1

a fuzzy comarison is what you need - there is code here that will compare two strings, and give you a score from 0 to 1 depending on how close they are. It will be up to you to decide how close they are to do automatic substitution.
example results:
server text fuzzy score
------- -------- -----------
hotmail hotmale 0.7619048
hotmail hot 0.4285714
hotmail notmail 0.8571429
hotmail NotEvenClose 0.1944444
hotmail hotmail 1
hotmail yellow 0.0952381
hotmail homtail 0.7142857
The the source code has been released under GNU Lesser GPL
in case of link rot, here's the code:
Public Function Fuzzy(ByVal s1 As String, ByVal s2 As String) As Single
Dim i As Integer, j As Integer, k As Integer, d1 As Integer, d2 As Integer, p As Integer
Dim c As String, a1 As String, a2 As String, f As Single, o As Single, w As Single
'
' ******* INPUT STRINGS CLEANSING *******
'
s1 = UCase(s1) 'input strings are converted to uppercase
d1 = Len(s1)
j = 1
For i = 1 To d1
c = Mid(s1, i, 1)
Select Case c
Case "0" To "9", "A" To "Z" 'filter the allowable characters
a1 = a1 & c 'a1 is what remains from s1 after filtering
j = j + 1
End Select
Next
If j = 1 Then Exit Function 'if s1 is empty after filtering
d1 = j - 1
s2 = UCase(s2)
d2 = Len(s2)
j = 1
For i = 1 To d2
c = Mid(s2, i, 1)
Select Case c
Case "0" To "9", "A" To "Z"
a2 = a2 & c
j = j + 1
End Select
Next
If j = 1 Then Exit Function
d2 = j - 1
k = d1
If d2 < d1 Then 'to prevent doubling the code below s1 must be made the shortest string,
'so we swap the variables
k = d2
d2 = d1
d1 = k
s1 = a2
s2 = a1
a1 = s1
a2 = s2
Else
s1 = a1
s2 = a2
End If
If k = 1 Then 'degenerate case, where the shortest string is just one character
If InStr(1, s2, s1, vbBinaryCompare) > 0 Then
Fuzzy = 1 / d2
Else
Fuzzy = 0
End If
Else '******* MAIN LOGIC HERE *******
i = 1
f = 0
o = 0
Do 'count the identical characters in s1 and s2 ("frequency analysis")
p = InStr(1, s2, Mid(s1, i, 1), vbBinaryCompare)
'search the character at position i from s1 in s2
If p > 0 Then 'found a matching character, at position p in s2
f = f + 1 'increment the frequency counter
s2 = Left(s2, p - 1) & "~" & Mid(s2, p + 1)
'replace the found character with one outside the allowable list
'(I used tilde here), to prevent re-finding
Do 'check the order of characters
If i >= k Then Exit Do 'no more characters to search
If Mid(s2, p + 1, 1) = Mid(s1, i + 1, 1) Then
'test if the next character is the same in the two strings
f = f + 1 'increment the frequency counter
o = o + 1 'increment the order counter
i = i + 1
p = p + 1
Else
Exit Do
End If
Loop
End If
If i >= k Then Exit Do
i = i + 1
Loop
If o > 0 Then o = o + 1 'if we got at least one match, adjust the order counter
'because two characters are required to define "order"
finish:
w = 2 'Weight of characters order match against characters frequency match;
'feel free to experiment, to get best matching results with your data.
'If only frequency is important, you can get rid of the second Do...Loop
'to significantly accelerate the code.
'By altering a bit the code above and the equation below you may get rid
'of the frequency parameter, since the order counter increments only for
'identical characters which are in the same order.
'However, I usually keep both parameters, since they offer maximum flexibility
'with a variety of data, and both should be maintained for this project
Fuzzy = (w * o + f) / (w + 1) / d2
End If
End Function

Answer 2

What you want to do is called Hamming codes (or hamming distance) -
try this