string comparison in %age or fuzzy string matching

I played around with this a little, and the best method that I came up with was to write my own function to analyze the strings. I actually Wrote a function that incorporates three tests as separate functions.

Test1 compares the length of the two strings to see if they are very close to the same size.
Test2 compares the strings letter by letter from front to back and rates them based on matching letters.
Test3 Compares the strings letter by letter from back to front (In reverse of the other one)

Then I take all of the results, average them, and compare this result to my predefined tolerance level. If the result is more that the tolerance setting, it returns true, if not it returns false.

Here is the code... in my form I had two text fields, a button and a label. btnTest is the button... txtString1 as the first text box... txtString2 as the 2nd text box... and lblResult as the label...

Public Class frmMain

    Private Sub btnTest_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnTest.Click
        lblResult.Text = CStr(compareStrings(txtSring1.Text, txtString2.Text, 80D))
    End Sub

    Private Function compareStrings(ByVal str1 As String, ByVal str2 As String, ByVal tolerance As Decimal) As Boolean

        Dim decTest1 As Decimal = test1(str1, str2, 1)
        Dim dectest2 As Decimal = test2(str1, str2)
        Dim decTest3 As Decimal = test3(str1, str2)

        Dim decAverage As Decimal = ((decTest1 + dectest2 + decTest3) / 3)
        If decAverage >= tolerance Then
            Return True
        Else
            Return False
        End If
    End Function

    Private Function test1(ByVal string1 As String, ByVal string2 As String, ByVal tolerance As Integer) As Decimal
        Dim int1 As Integer = string1.Length
        Dim int2 As Integer = string2.Length
        Dim intDifference As Integer = int1 - int2
        intDifference = Math.Abs(intDifference)
        Select Case intDifference
            Case 0
                Return 100D
            Case Is > 0
                'determine how much each character is worth, and subract that much for each
                'character that you are off
                Return (100 / string1.Length) * (string1.Length - intDifference)
        End Select
    End Function

    Private Function test2(ByVal string1 As String, ByVal string2 As String) As Decimal
        Dim I As Integer
        Dim chardiff As Integer
        chardiff = string1.Length - string2.Length
        Dim Charval As Decimal

        Select Case chardiff
            Case Is < 0
                'string2 is longer than string1
                Charval = 100 / string2.Length
            Case 0
                'The two strings are equal
                Charval = 100 / string1.Length
            Case Is > 0
                'string1 is longer than string2
                Charval = 100 / string1.Length
        End Select

        Dim totalVal As Decimal = 0
        If chardiff >= 0 Then
            For I = 0 To string1.Length - 1
                If string1.Chars(I) = string2.Chars(I) Then
                    totalVal += Charval
                End If
            Next
        Else
            For I = 0 To string2.Length - 1
                If string1.Chars(I) = string2.Chars(I) Then
                    totalVal += Charval
                End If
            Next
        End If

        Return totalVal
    End Function

    Private Function test3(ByVal string1 As String, ByVal string2 As String) As Decimal
        Dim I As Integer
        Dim chardiff As Integer
        chardiff = string1.Length - string2.Length
        Dim Charval As Decimal

        Select Case chardiff
            Case Is < 0
                'string2 is longer than string1
                Charval = 100 / string2.Length
            Case 0
                'The two strings are equal
                Charval = 100 / string1.Length
            Case Is > 0
                'string1 is longer than string2
                Charval = 100 / string1.Length
        End Select

        Dim totalVal As Decimal = 0
        If chardiff >= 0 Then
            For I = string1.Length - 1 To 0 Step -1

                If string1.Chars(I) = string2.Chars(I - chardiff) Then
                    totalVal += Charval
                End If
            Next
        Else
            For I = string2.Length - 1 To 0 Step -1
                If string1.Chars(I) = string2.Chars(I) Then
                    totalVal += Charval
                End If
            Next
        End If

        Return totalVal
    End Function
End Class

If you want to test this out in your application, you can copy the three functions into your app... compareStrings, test1, test2, and test3... and then call comparestrings with the proper parameters where you want to compare strings. In CompareStrings the first argument is the string you are trying to match... the second argument is the string you are testing as a possible match, and the third argument ... the tolerance setting ... is a decimal representative of the percentage match you are desiring... I would recommend 80... this will basically match every pair if there is only one letter off... usually even if a letter has been added... you can play around with that setting to make the match more strict or more lenient.

I hope this is a help.