Added jaccard_distance function

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 - Added support for binary vectors to HNSW
 - Added `hamming_distance` function
+- Added `jaccard_distance` function
 - Added `quantize_binary` function
 
 ## 0.6.2 (2024-03-18)

README.md

@@ -728,6 +728,7 @@ Operator | Description | Added
 Function | Description | Added
 --- | --- | ---
 hamming_distance(bit, bit) → double precision | Hamming distance | 0.7.0
+jaccard_distance(bit, bit) → double precision | Jaccard distance | 0.7.0
 
 ## Installation Notes - Linux and Mac
 

sql/vector--0.6.2--0.7.0.sql

@@ -7,6 +7,9 @@ CREATE FUNCTION quantize_binary(vector) RETURNS bit
 CREATE FUNCTION hamming_distance(bit, bit) RETURNS float8
 	AS 'MODULE_PATHNAME' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
 
+CREATE FUNCTION jaccard_distance(bit, bit) RETURNS float8
+	AS 'MODULE_PATHNAME' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
+
 CREATE OPERATOR <~> (
 	LEFTARG = bit, RIGHTARG = bit, PROCEDURE = hamming_distance,
 	COMMUTATOR = '<~>'

sql/vector.sql

@@ -296,6 +296,9 @@ CREATE OPERATOR CLASS vector_cosine_ops
 CREATE FUNCTION hamming_distance(bit, bit) RETURNS float8
 	AS 'MODULE_PATHNAME' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
 
+CREATE FUNCTION jaccard_distance(bit, bit) RETURNS float8
+	AS 'MODULE_PATHNAME' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
+
 CREATE OPERATOR <~> (
 	LEFTARG = bit, RIGHTARG = bit, PROCEDURE = hamming_distance,
 	COMMUTATOR = '<~>'

src/bitvector.c

@@ -58,3 +58,32 @@ hamming_distance(PG_FUNCTION_ARGS)
 
 	PG_RETURN_FLOAT8((double) distance);
 }
+
+/*
+ * Get the Jaccard distance between two bit strings
+ */
+PGDLLEXPORT PG_FUNCTION_INFO_V1(jaccard_distance);
+Datum
+jaccard_distance(PG_FUNCTION_ARGS)
+{
+	VarBit	   *a = PG_GETARG_VARBIT_P(0);
+	VarBit	   *b = PG_GETARG_VARBIT_P(1);
+	unsigned char *ax = VARBITS(a);
+	unsigned char *bx = VARBITS(b);
+	uint64		aa;
+	uint64		bb;
+	uint64		ab = 0;
+
+	CheckBitLengths(VARBITLEN(a), VARBITLEN(b));
+
+	/* TODO Improve performance */
+	aa = pg_popcount((char *) ax, VARBITBYTES(a));
+	bb = pg_popcount((char *) bx, VARBITBYTES(b));
+	for (uint32 i = 0; i < VARBITBYTES(a); i++)
+		ab += pg_number_of_ones[ax[i] & bx[i]];
+
+	if (ab == 0)
+		PG_RETURN_FLOAT8(1);
+
+	PG_RETURN_FLOAT8(1 - (ab / ((double) (aa + bb - ab))));
+}

test/expected/functions.out

@@ -234,6 +234,38 @@ SELECT hamming_distance(B'111', B'000');
 
 SELECT hamming_distance(B'111', B'00');
 ERROR:  different bit lengths 3 and 2
+SELECT jaccard_distance(B'1111', B'1111');
+ jaccard_distance 
+------------------
+                0
+(1 row)
+
+SELECT jaccard_distance(B'1111', B'1110');
+ jaccard_distance 
+------------------
+             0.25
+(1 row)
+
+SELECT jaccard_distance(B'1111', B'1100');
+ jaccard_distance 
+------------------
+              0.5
+(1 row)
+
+SELECT jaccard_distance(B'1111', B'1000');
+ jaccard_distance 
+------------------
+             0.75
+(1 row)
+
+SELECT jaccard_distance(B'1111', B'0000');
+ jaccard_distance 
+------------------
+                1
+(1 row)
+
+SELECT jaccard_distance(B'1111', B'000');
+ERROR:  different bit lengths 4 and 3
 SELECT quantize_binary('[1,0,-1]');
  quantize_binary 
 -----------------

test/sql/functions.sql

@@ -54,6 +54,13 @@ SELECT hamming_distance(B'111', B'100');
 SELECT hamming_distance(B'111', B'000');
 SELECT hamming_distance(B'111', B'00');
 
+SELECT jaccard_distance(B'1111', B'1111');
+SELECT jaccard_distance(B'1111', B'1110');
+SELECT jaccard_distance(B'1111', B'1100');
+SELECT jaccard_distance(B'1111', B'1000');
+SELECT jaccard_distance(B'1111', B'0000');
+SELECT jaccard_distance(B'1111', B'000');
+
 SELECT quantize_binary('[1,0,-1]');
 SELECT quantize_binary('[0,0.1,-0.2,-0.3,0.4,0.5,0.6,-0.7,0.8,-0.9,1]');