[dedupe] Jaccard similarity

src/jaccard.c

@@ -0,0 +1,27 @@
+#include "jaccard.h"
+
+
+double jaccard_similarity(khash_t(str_set) *s1, khash_t(str_set) *s2) {
+    if (s1 == NULL || s2 == NULL) return -1.0;
+
+    size_t set_intersection = 0;
+    size_t set_union = 0;
+
+    khiter_t k;
+    const char *key;
+
+    kh_foreach_key(s1, key, {
+        k = kh_get(str_set, s2, key);
+        if (k != kh_end(s2)) {
+            set_intersection++;
+        } else {
+            set_union++;
+        }
+    });
+
+    // set_union contains all the keys that were in s1 but not s2
+    // so just add all the keys in s2 to complete the union
+    set_union += kh_size(s2);
+
+    return (double)set_intersection / set_union;
+}

src/jaccard.h

@@ -0,0 +1,11 @@
+#ifndef JACCARD_H
+#define JACCARD_H
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "collections.h"
+
+double jaccard_similarity(khash_t(str_set) *s1, khash_t(str_set) *s2);
+
+#endif