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Levenshtein Algorithm in Visual Basic

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4.52/5 (8 votes)
3 Jan 2015CPOL1 min read 28.1K   6   6
How to calculate the distance between two strings according to Levenshtein algorithm

Introduction

Levenshtein's distance measures the minimum number of character edits required to change a word into another. In this tip, we'll see a simple implementation of the Levenshtein algorithm in Visual Basic. It will be useful in several situations, when managing - for example - large amount of text, and we are in need of fast and massive modifications in our data, to spot and correct typos, or to match `string`s in terms of similarity, and not simply in terms of equal/not equal. Levenshtein's algorithm allows to compute a score regarding `string `similarity. We'll see how in a moment.

Standard Levenshtein Algorithm

Here follows the standard Levenshtein implementation in VB.NET, according to the algorithm as shown at Wikipedia.

VB.NET
```Public Function Levenshtein(ByVal s As String, ByVal t As String) As Integer
Dim n As Integer = s.Length
Dim m As Integer = t.Length
Dim d(n + 1, m + 1) As Integer

If n = 0 Then
Return m
End If
If m = 0 Then
Return n
End If

Dim i As Integer
Dim j As Integer

For i = 0 To n
d(i, 0) = i
Next
For j = 0 To m
d(0, j) = j
Next
For i = 1 To n
For j = 1 To m
Dim cost As Integer
If t(j - 1) = s(i - 1) Then
cost = 0
Else
cost = 1
End If
d(i, j) = Math.Min(Math.Min(d(i - 1, j) + 1, d(i, j - 1) + 1), d(i - 1, j - 1) + cost)
Next
Next
Return d(n, m)
End Function```

Examples

Using the above function(s) is trivial: it's sufficient to call it by passing two `string`s, plus the optional boolean flag for case-sensitivity check. Some examples could be:

VB.NET
```MsgBox(Levenshtein("Inwards", "inwards").ToString)       ' Returns 1
MsgBox(Levenshtein("Inwards", "inwards").ToString)       ' Returns 1
MsgBox(Levenshtein("towards", "towards").ToString)       ' Returns 0
MsgBox(Levenshtein("dinner", "breakfast").ToString)      ' Returns 9
MsgBox(Levenshtein("breakfast", "braekfast").ToString)   ' Returns 2

MsgBox(Levenshtein("efficient", "sufficient").ToString)  ' Returns 2
MsgBox(Levenshtein("grandma", "anathema").ToString)      ' Returns 5
MsgBox(Levenshtein("aunt", "ant").ToString)              ' Returns 1```

The results (1, 0, 0, 9, 2, 2, 5, 1) are the Levenshtein's distances between given `string`s, i.e., a score regarding `string`s similarity. The lower the score, the nearer are the two entities. A value of zero means, obviously, a total convergence of the two. We could use a function like this (with predetermined conditions to be satisfied, like "the score must not exceed 3", for example) to correct typos (as in the "breakfast - braekfast" example), or to search for differences in hypothetical data (like "new York - New York"), and so on.

History

• 2015-01-06 Added standard algorithm, revised text, revised code
• 2015-01-03 First release for CodeProject

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Written By
Software Developer
Italy
Working in IT since 2003 as Software Developer for Essetre Srl, a company in Northern Italy.
I was awarded in 2014, 2015 and 2016 with Microsoft MVP, for Visual Studio and Development Technologies expertise. My technology interests and main skills are in .NET Framework, Visual Basic, Visual C# and SQL Server, but i'm proficient in PHP and MySQL also.

Comments and Discussions

 First Prev Next
 My vote of 1 Etter Frédéric5-Jan-15 21:43 Etter Frédéric 5-Jan-15 21:43
 Wrong code - Sorry Etter Frédéric5-Jan-15 21:42 Etter Frédéric 5-Jan-15 21:42
 You should review the algorithm on wikipedia (or change the name of your function ). Fred
 Re: Wrong code - Sorry Emiliano Musso5-Jan-15 22:21 Emiliano Musso 5-Jan-15 22:21
 Re: Wrong code - Sorry Etter Frédéric6-Jan-15 2:46 Etter Frédéric 6-Jan-15 2:46
 Re: Wrong code - Sorry Emiliano Musso6-Jan-15 6:02 Emiliano Musso 6-Jan-15 6:02
 My vote of 1 Etter Frédéric5-Jan-15 21:36 Etter Frédéric 5-Jan-15 21:36
 Last Visit: 31-Dec-99 18:00     Last Update: 9-Sep-24 2:48 Refresh 1

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