StringDistances.jl/src/edit.jl

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##############################################################################
##
## Hamming
##
##############################################################################
function evaluate(dist::Hamming, s1::Union{AbstractString, Missing}, s2::Union{AbstractString, Missing})
current = abs(length(s2) - length(s1))
for (ch1, ch2) in zip(s1, s2)
current += ch1 != ch2
end
return current
end
evaluate(dist::Hamming, s1::Missing, s2::AbstractString) = missing
evaluate(dist::Hamming, s1::AbstractString, s2::Missing) = missing
##############################################################################
##
## Jaro
##
##############################################################################
"""
Jaro()
Creates the Jaro metric
The Jaro distance is defined as
``1 - (m / |s1| + m / |s2| + (m - t) / m) / 3``
where ``m`` is the number of matching characters and
``t`` is half the number of transpositions.
"""
struct Jaro <: SemiMetric end
## http://alias-i.com/lingpipe/docs/api/com/aliasi/spell/JaroWinklerDistance.html
function evaluate(dist::Jaro, s1::Union{AbstractString, Missing}, s2::Union{AbstractString, Missing})
(ismissing(s1) | ismissing(s2)) && return missing
s1, s2 = reorder(s1, s2)
len1, len2 = length(s1), length(s2)
# if both are empty, m = 0 so should be 1.0 according to wikipedia. Add this line so that not the case
len2 == 0 && return 0.0
maxdist = max(0, div(len2, 2) - 1)
flag = fill(false, len2)
prevstate1 = firstindex(s1)
i1_match = fill(prevstate1, len1)
# m counts number matching characters
m = 0
i1 = 1
i2 = 1
x1 = iterate(s1)
x2 = iterate(s2)
while x1 !== nothing
ch1, state1 = x1
if i2 <= i1 - maxdist - 1
ch2, state2 = x2
i2 += 1
x2 = iterate(s2, state2)
end
i2curr = i2
x2curr = x2
while x2curr !== nothing
i2curr > i1 + maxdist && break
ch2, state2 = x2curr
if (ch1 == ch2) && !flag[i2curr]
m += 1
flag[i2curr] = true
i1_match[m] = prevstate1
break
end
x2curr = iterate(s2, state2)
i2curr += 1
end
x1 = iterate(s1, state1)
i1 += 1
prevstate1 = state1
end
m == 0 && return 1.0
# t counts number of transpositions
t = 0
i1 = 0
i2 = 0
for ch2 in s2
i2 += 1
if flag[i2]
i1 += 1
t += ch2 != iterate(s1, i1_match[i1])[1]
end
end
return 1.0 - (m / len1 + m / len2 + (m - t/2) / m) / 3.0
end
##############################################################################
##
## Levenshtein
##
## Return max_dist +1 if distance higher than max_dist
## This makes it possible to differentiate distance equalt to max_dist vs strictly higher
## This is important for find_all
##
##############################################################################
"""
Levenshtein()
Creates the Levenshtein metric
The Levenshtein distance is the minimum number of operations (consisting of insertions, deletions, substitutions of a single character) required to change one string into the other.
"""
struct Levenshtein <: SemiMetric end
## Source: http://blog.softwx.net/2014/12/optimizing-levenshtein-algorithm-in-c.html
function evaluate(dist::Levenshtein, s1::Union{AbstractString, Missing}, s2::Union{AbstractString, Missing}; max_dist = nothing)
(ismissing(s1) | ismissing(s2)) && return missing
s1, s2 = reorder(s1, s2)
len1, len2 = length(s1), length(s2)
max_dist !== nothing && len2 - len1 > max_dist && return max_dist + 1
# prefix common to both strings can be ignored
k, x1, x2start = remove_prefix(s1, s2)
x1 == nothing && return len2 - k
# distance initialized to first row of matrix
# => distance between "" and s2[1:i}
v0 = collect(1:(len2 - k))
current = 0
i1 = 1
while x1 !== nothing
ch1, state1 = x1
left = i1 - 1
current = i1 - 1
min_dist = i1 - 2
i2 = 1
x2 = x2start
while x2 !== nothing
ch2, state2 = x2
# update
above, current, left = current, left, v0[i2]
if ch1 != ch2
current = min(current + 1, above + 1, left + 1)
end
min_dist = min(min_dist, left)
v0[i2] = current
x2 = iterate(s2, state2)
i2 += 1
end
max_dist !== nothing && min_dist > max_dist && return max_dist + 1
x1 = iterate(s1, state1)
i1 += 1
end
max_dist !== nothing && current > max_dist && return max_dist + 1
return current
end
##############################################################################
##
## Damerau Levenshtein
##
##############################################################################
"""
DamerauLevenshtein()
Creates the DamerauLevenshtein metric
The DamerauLevenshtein distance is the minimum number of operations (consisting of insertions, deletions or substitutions of a single character, or transposition of two adjacent characters) required to change one string into the other.
"""
struct DamerauLevenshtein <: SemiMetric end
## http://blog.softwx.net/2015/01/optimizing-damerau-levenshtein_15.html
function evaluate(dist::DamerauLevenshtein, s1::Union{AbstractString, Missing}, s2::Union{AbstractString, Missing}; max_dist = nothing)
(ismissing(s1) | ismissing(s2)) && return missing
s1, s2 = reorder(s1, s2)
len1, len2 = length(s1), length(s2)
max_dist !== nothing && len2 - len1 > max_dist && return max_dist + 1
# prefix common to both strings can be ignored
k, x1, x2start = remove_prefix(s1, s2)
(x1 == nothing) && return len2 - k
v0 = collect(1:(len2 - k))
v2 = similar(v0)
if max_dist !== nothing
offset = 1 + max_dist - (len2 - len1)
i2_start = 1
i2_end = max_dist
end
i1 = 1
current = i1
prevch1, = x1
while x1 !== nothing
ch1, state1 = x1
left = (i1 - 1)
current = i1
nextTransCost = 0
prevch2, = x2start
if max_dist !== nothing
i2_start += (i1 > offset) ? 1 : 0
i2_end = min(i2_end + 1, len2)
end
x2 = x2start
i2 = 1
while x2 !== nothing
ch2, state2 = x2
if max_dist == nothing || (i2_start <= i2 <= i2_end)
above = current
thisTransCost = nextTransCost
nextTransCost = v2[i2]
# cost of diagonal (substitution)
v2[i2] = current = left
# left now equals current cost (which will be diagonal at next iteration)
left = v0[i2]
if ch1 != ch2
# insertion
if left < current
current = left
end
# deletion
if above < current
current = above
end
current += 1
if (i1 != 1) & (i2 != 1) & (ch1 == prevch2) & (prevch1 == ch2)
thisTransCost += 1
if thisTransCost < current
current = thisTransCost
end
end
end
v0[i2] = current
end
x2 = iterate(s2, state2)
i2 += 1
prevch2 = ch2
end
max_dist !== nothing && v0[i1 + len2 - len1] > max_dist && return max_dist + 1
x1 = iterate(s1, state1)
i1 += 1
prevch1 = ch1
end
max_dist !== nothing && current > max_dist && return max_dist + 1
return current
end
##############################################################################
##
## Ratcliff/Obershelp
##
##############################################################################
"""
RatcliffObershelp()
Creates the RatcliffObershelp metric
The distance between two strings is defined as one minus the number of matching characters divided by the total number of characters in the two strings. Matching characters are those in the longest common subsequence plus, recursively, matching characters in the unmatched region on either side of the longest common subsequence.
"""
struct RatcliffObershelp <: PreMetric end
function evaluate(dist::RatcliffObershelp, s1::Union{AbstractString, Missing}, s2::Union{AbstractString, Missing})
(ismissing(s1) | ismissing(s2)) && return missing
n_matched = sum(last.(matching_blocks(s1, s2)))
len1, len2 = length(s1), length(s2)
len1 + len2 == 0 ? 0. : 1.0 - 2 * n_matched / (len1 + len2)
end
function matching_blocks(s1::AbstractString, s2::AbstractString)
matching_blocks!(Set{Tuple{Int, Int, Int}}(), s1, s2, length(s1), length(s2), 1, 1)
end
function matching_blocks!(x::Set{Tuple{Int, Int, Int}}, s1::AbstractString, s2::AbstractString, len1::Integer, len2::Integer, start1::Integer, start2::Integer)
a = longest_common_substring(s1, s2, len1 , len2)
# exit if there is no common substring
a[3] == 0 && return x
# add the info of the common to the existing set
push!(x, (a[1] + start1 - 1, a[2] + start2 - 1, a[3]))
# add the longest common substring that happens before
s1before = SubString(s1, 1, nextind(s1, 0, a[1] - 1))
s2before = SubString(s2, 1, nextind(s2, 0, a[2] - 1))
matching_blocks!(x, s1before, s2before, a[1] - 1, a[2] - 1, start1, start2)
# add the longest common substring that happens after
s1after = SubString(s1, nextind(s1, 0, a[1] + a[3]), lastindex(s1))
s2after = SubString(s2, nextind(s2, 0, a[2] + a[3]), lastindex(s2))
matching_blocks!(x, s1after, s2after, len1 - (a[1] + a[3]) + 1, len2 - (a[2] + a[3]) + 1, start1 + a[1] + a[3] - 1, start2 + a[2] + a[3] - 1)
return x
end