Esta discussão foi realmente útil, obrigado. Converti o algoritmo em VBA para uso com o Excel e escrevi algumas versões de uma função de planilha, uma para comparação simples de um par de cadeias, a outra para comparar uma cadeia com um intervalo / matriz de cadeias. A versão strSimLookup retorna a última melhor correspondência como uma string, índice de matriz ou métrica de similaridade.
Essa implementação produz os mesmos resultados listados no exemplo da Amazon no site de Simon White, com algumas pequenas exceções em correspondências com baixa pontuação; não sei onde a diferença se aproxima, poderia ser a função Split do VBA, mas não investiguei, pois está funcionando bem para meus propósitos.
'Implements functions to rate how similar two strings are on
'a scale of 0.0 (completely dissimilar) to 1.0 (exactly similar)
'Source: http://www.catalysoft.com/articles/StrikeAMatch.html
'Author: Bob Chatham, bob.chatham at gmail.com
'9/12/2010
Option Explicit
Public Function stringSimilarity(str1 As String, str2 As String) As Variant
'Simple version of the algorithm that computes the similiarity metric
'between two strings.
'NOTE: This verision is not efficient to use if you're comparing one string
'with a range of other values as it will needlessly calculate the pairs for the
'first string over an over again; use the array-optimized version for this case.
Dim sPairs1 As Collection
Dim sPairs2 As Collection
Set sPairs1 = New Collection
Set sPairs2 = New Collection
WordLetterPairs str1, sPairs1
WordLetterPairs str2, sPairs2
stringSimilarity = SimilarityMetric(sPairs1, sPairs2)
Set sPairs1 = Nothing
Set sPairs2 = Nothing
End Function
Public Function strSimA(str1 As Variant, rRng As Range) As Variant
'Return an array of string similarity indexes for str1 vs every string in input range rRng
Dim sPairs1 As Collection
Dim sPairs2 As Collection
Dim arrOut As Variant
Dim l As Long, j As Long
Set sPairs1 = New Collection
WordLetterPairs CStr(str1), sPairs1
l = rRng.Count
ReDim arrOut(1 To l)
For j = 1 To l
Set sPairs2 = New Collection
WordLetterPairs CStr(rRng(j)), sPairs2
arrOut(j) = SimilarityMetric(sPairs1, sPairs2)
Set sPairs2 = Nothing
Next j
strSimA = Application.Transpose(arrOut)
End Function
Public Function strSimLookup(str1 As Variant, rRng As Range, Optional returnType) As Variant
'Return either the best match or the index of the best match
'depending on returnTYype parameter) between str1 and strings in rRng)
' returnType = 0 or omitted: returns the best matching string
' returnType = 1 : returns the index of the best matching string
' returnType = 2 : returns the similarity metric
Dim sPairs1 As Collection
Dim sPairs2 As Collection
Dim metric, bestMetric As Double
Dim i, iBest As Long
Const RETURN_STRING As Integer = 0
Const RETURN_INDEX As Integer = 1
Const RETURN_METRIC As Integer = 2
If IsMissing(returnType) Then returnType = RETURN_STRING
Set sPairs1 = New Collection
WordLetterPairs CStr(str1), sPairs1
bestMetric = -1
iBest = -1
For i = 1 To rRng.Count
Set sPairs2 = New Collection
WordLetterPairs CStr(rRng(i)), sPairs2
metric = SimilarityMetric(sPairs1, sPairs2)
If metric > bestMetric Then
bestMetric = metric
iBest = i
End If
Set sPairs2 = Nothing
Next i
If iBest = -1 Then
strSimLookup = CVErr(xlErrValue)
Exit Function
End If
Select Case returnType
Case RETURN_STRING
strSimLookup = CStr(rRng(iBest))
Case RETURN_INDEX
strSimLookup = iBest
Case Else
strSimLookup = bestMetric
End Select
End Function
Public Function strSim(str1 As String, str2 As String) As Variant
Dim ilen, iLen1, ilen2 As Integer
iLen1 = Len(str1)
ilen2 = Len(str2)
If iLen1 >= ilen2 Then ilen = ilen2 Else ilen = iLen1
strSim = stringSimilarity(Left(str1, ilen), Left(str2, ilen))
End Function
Sub WordLetterPairs(str As String, pairColl As Collection)
'Tokenize str into words, then add all letter pairs to pairColl
Dim Words() As String
Dim word, nPairs, pair As Integer
Words = Split(str)
If UBound(Words) < 0 Then
Set pairColl = Nothing
Exit Sub
End If
For word = 0 To UBound(Words)
nPairs = Len(Words(word)) - 1
If nPairs > 0 Then
For pair = 1 To nPairs
pairColl.Add Mid(Words(word), pair, 2)
Next pair
End If
Next word
End Sub
Private Function SimilarityMetric(sPairs1 As Collection, sPairs2 As Collection) As Variant
'Helper function to calculate similarity metric given two collections of letter pairs.
'This function is designed to allow the pair collections to be set up separately as needed.
'NOTE: sPairs2 collection will be altered as pairs are removed; copy the collection
'if this is not the desired behavior.
'Also assumes that collections will be deallocated somewhere else
Dim Intersect As Double
Dim Union As Double
Dim i, j As Long
If sPairs1.Count = 0 Or sPairs2.Count = 0 Then
SimilarityMetric = CVErr(xlErrNA)
Exit Function
End If
Union = sPairs1.Count + sPairs2.Count
Intersect = 0
For i = 1 To sPairs1.Count
For j = 1 To sPairs2.Count
If StrComp(sPairs1(i), sPairs2(j)) = 0 Then
Intersect = Intersect + 1
sPairs2.Remove j
Exit For
End If
Next j
Next i
SimilarityMetric = (2 * Intersect) / Union
End Function