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#!python3
"""
Operations on strings:
- calculate distance between two strings
- transform strings with transformation codes
"""
#### DISTANCE CALCULATIONS
def longestCommonSubstring (s1, s2):
"longest common substring"
# http://en.wikipedia.org/wiki/Longest_common_substring_problem
# http://en.wikibooks.org/wiki/Algorithm_implementation/Strings/Longest_common_substring
M = [ [0]*(1+len(s2)) for i in range(1+len(s1)) ]
longest, x_longest = 0, 0
lMatrix = [ [0]*(1+len(s2)) for i in range(1+len(s1)) ]
nLongest, nLongestX = 0, 0
for x in range(1, 1+len(s1)):
for y in range(1, 1+len(s2)):
if s1[x-1] == s2[y-1]:
M[x][y] = M[x-1][y-1] + 1
if M[x][y] > longest:
longest = M[x][y]
x_longest = x
lMatrix[x][y] = lMatrix[x-1][y-1] + 1
if lMatrix[x][y] > nLongest:
nLongest = lMatrix[x][y]
nLongestX = x
else:
M[x][y] = 0
return s1[x_longest-longest : x_longest]
lMatrix[x][y] = 0
return s1[nLongestX-nLongest : nLongestX]
def distanceDamerauLevenshtein (s1, s2):
"distance of Damerau-Levenshtein between <s1> and <s2>"
# https://fr.wikipedia.org/wiki/Distance_de_Damerau-Levenshtein
d = {}
nLen1 = len(s1)
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return len(s1)
nLen1, nLen2 = len(s1), len(s2)
i1, i2 = 0, 0 # Cursors for each string
nLargestCS = 0 # Largest common substring
nLocalCS = 0 # Local common substring
nTrans = 0 # Number of transpositions ('ab' vs 'ba')
lOffset = [] # Offset pair array, for computing the transpositions
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nLocalCS = 0
i1 = i2 = min(i1, i2)
nLargestCS += nLocalCS
return round(max(nLen1, nLen2) - nLargestCS + nTrans)
def showDistance (s1, s2):
"display Damerau-Levenshtein distance and Sift4 distance between <s1> and <s2>"
print("Damerau-Levenshtein: " + s1 + "/" + s2 + " = " + distanceDamerauLevenshtein(s1, s2))
print("Sift4:" + s1 + "/" + s2 + " = " + distanceSift4(s1, s2))
#### STEMMING OPERATIONS
## No stemming
def noStemming (sFlex, sStem):
"return <sStem>"
return sStem
def rebuildWord (sFlex, cmd1, cmd2):
if cmd1 == "_":
def rebuildWord (sFlex, sCode1, sCode2):
""" Change <sFlex> with codes (each inserts a char at a defined possition).
<I forgot what purpose it has…>
"""
if sCode1 == "_":
return sFlex
n, c = cmd1.split(":")
s = s[:n] + c + s[n:]
if cmd2 == "_":
return s
n, c = cmd2.split(":")
return s[:n] + c + s[n:]
n, c = sCode1.split(":")
sFlex = sFlex[:n] + c + sFlex[n:]
if sCode2 == "_":
return sFlex
n, c = sCode2.split(":")
return sFlex[:n] + c + sFlex[n:]
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if sFlex == sStem:
return "0"
jSfx = 0
for i in range(min(len(sFlex), len(sStem))):
if sFlex[i] != sStem[i]:
break
jSfx += 1
return chr(len(sFlex)-jSfx+48) + sStem[jSfx:]
return chr(len(sFlex)-jSfx+48) + sStem[jSfx:]
def changeWordWithSuffixCode (sWord, sSfxCode):
"apply transformation code <sSfxCode> on <sWord> and return the result string"
if sSfxCode == "0":
return sWord
return sWord[:-(ord(sSfxCode[0])-48)] + sSfxCode[1:] if sSfxCode[0] != '0' else sWord + sSfxCode[1:]
# Prefix and suffix
def defineAffixCode (sFlex, sStem):
""" Returns a string defining how to get stem from flexion. Examples:
"0" if stem = flexion
"stem" if no common substring
"n(pfx)/m(sfx)"
with n and m: chars with numeric meaning, "0" = 0, "1" = 1, ... ":" = 10, etc. (See ASCII table.) Says how many letters to strip from flexion.
pfx [optional]: string to add before the flexion
pfx [optional]: string to add before the flexion
sfx [optional]: string to add after the flexion
"""
if sFlex == sStem:
return "0"
# is stem a substring of flexion?
n = sFlex.find(sStem)
if n >= 0:
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n = sFlex.find(sSubs)
m = len(sFlex) - (len(sSubs)+n)
return chr(n+48) + sPfx + "/" + chr(m+48) + sSfx
return sStem
def changeWordWithAffixCode (sWord, sAffCode):
"apply transformation code <sAffCode> on <sWord> and return the result string"
if sAffCode == "0":
return sWord
if '/' not in sAffCode:
return sAffCode
sPfxCode, sSfxCode = sAffCode.split('/')
sWord = sPfxCode[1:] + sWord[(ord(sPfxCode[0])-48):]
sWord = sPfxCode[1:] + sWord[(ord(sPfxCode[0])-48):]
return sWord[:-(ord(sSfxCode[0])-48)] + sSfxCode[1:] if sSfxCode[0] != '0' else sWord + sSfxCode[1:]
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