Merge pull request #16 from rhasspy/generic_levenshtein

add custom weights for levenshtein

.gitignore

@@ -1,4 +1,6 @@
 .vscode/
+__pycache__/
+.idea/
 rapidfuzz.egg-info/
 dist/
 *.data

cpp/src/levenshtein.hpp

@@ -87,6 +87,9 @@ namespace levenshtein {
     template<typename CharT, typename MaxDistance=std::nullopt_t>
     std::size_t weighted_distance(string_view_vec<CharT> sentence1, string_view_vec<CharT> sentence2, MaxDistance max_distance=std::nullopt);
 
+
+    size_t generic_distance(std::wstring_view source, std::wstring_view target, size_t insert_cost = 1, size_t delete_cost = 1, size_t replace_cost = 1);
+
     /**
     * Calculates a normalized score of the weighted Levenshtein algorithm between 0.0 and
     * 1.0 (inclusive), where 1.0 means the sequences are the same.
@@ -283,16 +286,20 @@ inline std::size_t levenshtein::distance(std::wstring_view sentence1, std::wstri
   std::iota(cache.begin(), cache.end(), 0);
 
   for (const auto &char1 : sentence1) {
-    size_t temp = cache[0]++;
+    auto cache_iter = cache.begin();
+    size_t temp = *cache_iter;
+    *cache_iter += 1;
+
 		for (size_t j = 1; j < cache.size(); ++j)
 		{
-			size_t p = cache[j - 1];
-			size_t r = cache[j];
+			size_t p = *cache_iter;
+      ++cache_iter;
+			size_t r = *cache_iter;
 			temp = std::min(
 			    std::min(r, p) + 1,
 			    temp + (char1 == sentence2[j - 1] ? 0 : 1)
 			);
-			std::swap(cache[j], temp);
+			std::swap(*cache_iter, temp);
 		}
   }
   return cache.back();
@@ -481,6 +488,44 @@ inline std::size_t levenshtein::weighted_distance_impl(std::basic_string_view<Ch
 }
 
 
+inline size_t levenshtein::generic_distance(std::wstring_view sentence1, std::wstring_view sentence2,
+                                      size_t insert_cost, size_t delete_cost, size_t replace_cost)
+{
+    remove_common_affix(sentence1, sentence2);
+    if (sentence1.size() > sentence2.size()) {
+        std::swap(sentence1, sentence2);
+        std::swap(insert_cost, delete_cost);
+    }
+
+    const size_t min_size = sentence1.size();
+    std::vector<size_t> cache(sentence1.size() + 1);
+
+    cache[0] = 0;
+    for (size_t i = 1; i < cache.size(); ++i) {
+        cache[i] = cache[i - 1] + delete_cost;
+    }
+
+    for (const auto &char2 : sentence2) {
+        auto cache_iter = cache.begin();
+        size_t temp = *cache_iter;
+        *cache_iter += insert_cost;
+
+        for (const auto &char1 : sentence1) {
+            if (char1 != char2) {
+                temp= std::min({
+                  *cache_iter + delete_cost,
+                  *(cache_iter+1) + insert_cost,
+                  temp + replace_cost
+                });
+            }
+            ++cache_iter;
+            std::swap(*cache_iter, temp);
+        }
+    }
+
+    return cache.back();
+}
+
 
 template<typename Sentence1, typename Sentence2>
 inline float levenshtein::normalized_weighted_distance(const Sentence1 &sentence1, const Sentence2 &sentence2, float min_ratio)

python/src/rapidfuzz.cpp

@@ -233,29 +233,32 @@ PYBIND11_MODULE(_rapidfuzz_cpp, m) {
         py::arg("s1"), py::arg("s2"), py::arg("score_cutoff") = 0);
 
     mlevenshtein.def("weighted_distance",
-        [](std::wstring_view s1, std::wstring_view s2){
-            return levenshtein::weighted_distance(s1, s2);
+        [](std::wstring_view s1, std::wstring_view s2, size_t insert_cost, size_t delete_cost, size_t replace_cost){
+            if (insert_cost == 1 && delete_cost == 1) {
+                if (replace_cost == 1) {
+                    return levenshtein::distance(s1, s2);
+                } else if (replace_cost == 2) {
+                    return levenshtein::weighted_distance(s1, s2);
+                }
+            }
+            return levenshtein::generic_distance(s1, s2, insert_cost, delete_cost, replace_cost);
         },
         R"pbdoc(
             Calculates the minimum number of insertions, deletions, and substitutions
-            required to change one sequence into the other according to Levenshtein.
-            Opposed to the normal distance function which has a cost of 1 for all edit operations,
-            it uses the following costs for edit operations:
-
-            edit operation | cost
-            :------------- | :---
-            Insert         | 1
-            Remove         | 1
-            Replace        | 2
+            required to change one sequence into the other according to Levenshtein with custom
+            costs for insertion, deletion and substitution
 
             Args:
                 s1 (str):  first string to compare
                 s2 (str):  second string to compare
+                insert_cost (int): cost for insertions
+                delete_cost (int): cost for deletions
+                replace_cost (int): cost for substitutions
 
             Returns:
                 int: weighted levenshtein distance between s1 and s2
         )pbdoc",
-        py::arg("s1"), py::arg("s2"));
+        py::arg("s1"), py::arg("s2"), py::arg("insert_cost")=1, py::arg("delete_cost")=1, py::arg("replace_cost")=1);
 
     mlevenshtein.def("normalized_weighted_distance",
         [](std::wstring_view s1, std::wstring_view s2, float score_cutoff){
@@ -263,6 +266,13 @@ PYBIND11_MODULE(_rapidfuzz_cpp, m) {
         },
         R"pbdoc(
             Calculates a normalized levenshtein distance based on levenshtein.weighted_distance
+            It uses the following costs for edit operations:
+
+            edit operation | cost
+            :------------- | :---
+            Insert         | 1
+            Remove         | 1
+            Replace        | 2
 
             Args:
                 s1 (str):  first string to compare