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Add Levenshtein distance functions to string lib #3648
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Original file line number | Diff line number | Diff line change | ||||||
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@@ -182,3 +182,66 @@ if not string.formatSI then | |||||||
return str .. siPrefix | ||||||||
end | ||||||||
end | ||||||||
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if not string.Levenshtein then | ||||||||
-- reuseable tables | ||||||||
local Levenshtein0 = {} | ||||||||
local Levenshtein1 = {} | ||||||||
local min = math.min | ||||||||
local ssub = string.sub | ||||||||
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--- Calculates edit distance of two strings, O(n*m) time, O(n) memory | ||||||||
---@param a string | ||||||||
---@param b string | ||||||||
---@return number | ||||||||
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function string.Levenshtein(a,b) | ||||||||
local lena = string.len(a) | ||||||||
local lenb = string.len(b) | ||||||||
local ssub = string.sub | ||||||||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. already defined above
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Levenshtein1[1] = 0 | ||||||||
for c = 0, lenb do -- initialize the first row | ||||||||
Levenshtein0[c+1] = c | ||||||||
end | ||||||||
for r = 1, lena do | ||||||||
--print(table.unpack(Levenshtein0)) | ||||||||
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Suggested change
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for c = 0, lenb do -- 16 ns/loop wtf | ||||||||
if c == 0 then | ||||||||
Levenshtein1[1] = r | ||||||||
else | ||||||||
Levenshtein1[c+1] = min( | ||||||||
min(Levenshtein0[c+1] + 1, Levenshtein1[c] + 1), | ||||||||
Levenshtein0[c] + (ssub(a,r,r) == ssub(b,c,c) and 0 or 1) | ||||||||
) | ||||||||
end | ||||||||
end | ||||||||
Levenshtein0, Levenshtein1 = Levenshtein1, Levenshtein0 -- swap rows | ||||||||
end | ||||||||
return Levenshtein1[lenb] | ||||||||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. The function gives incorrect output for at least these test cases: {
name = "returns the length of the non-empty string for one empty string",
args = { "", "apple" },
expected = 5,
},
{
name = "returns the length of the non-empty string for one empty string (reverse case)",
args = { "apple", "" },
expected = 5,
},
{
name = "returns 1 for strings differing by one character",
args = { "apple", "appla" },
expected = 1,
},
{
name = "returns the length of the longer string for completely different strings",
args = { "cat", "dogs" },
expected = 4,
}, This change fixes those tests:
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end | ||||||||
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--- Finds string that is closest to a in a table | ||||||||
---@param a string | ||||||||
---@param t table, primarily values are strings, keys can be strings too | ||||||||
---@return string, number bestresult, bestscore | ||||||||
function string.FindClosest(a,t) | ||||||||
local lena = string.len(a) | ||||||||
local bestscore = lena | ||||||||
local bestresult = a | ||||||||
for k,v in pairs(t) do | ||||||||
local b = (type(v) == 'string' and v) or (type(k) == 'string' and k) or "" -- whichever is string, or empty | ||||||||
if math.abs(string.len(b) - lena) < bestscore then -- heuristics | ||||||||
local distance = string.Levenshtein(a, b) | ||||||||
if distance < bestscore then | ||||||||
bestscore = distance | ||||||||
bestresult = b | ||||||||
end | ||||||||
end | ||||||||
end | ||||||||
return bestresult, bestscore | ||||||||
end | ||||||||
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-- print(string.Levenshtein(string.rep("asdfasdfasdfasdf", 1000), string.rep("asdfasdfasdfasda", 1000))) -- 5 seconds | ||||||||
-- print(string.FindClosest("apple", {"pear", "popple","bear","ple"})) | ||||||||
Comment on lines
+244
to
+246
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Suggested change
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end |
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rename to match other functions, and to make it a little more clear what it does
(and changes on related lines for this and
FindClosest
)