From 4f6c4850d9d33f58eba38d6c3f1eb4bb276c2109 Mon Sep 17 00:00:00 2001
From: Andrew Kane <andrew@ankane.org>
Date: Sun, 14 Apr 2024 22:59:28 -0700
Subject: [PATCH] Added l1_distance function for sparsevec [skip ci]

---
 sql/vector--0.6.2--0.7.0.sql          |  3 ++
 sql/vector.sql                        |  3 ++
 src/sparsevec.c                       | 49 +++++++++++++++++++++++++++
 test/expected/sparsevec_functions.out | 20 +++++++++++
 test/sql/sparsevec_functions.sql      |  5 +++
 5 files changed, 80 insertions(+)

diff --git a/sql/vector--0.6.2--0.7.0.sql b/sql/vector--0.6.2--0.7.0.sql
index b2db93e..220d331 100644
--- a/sql/vector--0.6.2--0.7.0.sql
+++ b/sql/vector--0.6.2--0.7.0.sql
@@ -344,6 +344,9 @@ CREATE FUNCTION inner_product(sparsevec, sparsevec) RETURNS float8
 CREATE FUNCTION cosine_distance(sparsevec, sparsevec) RETURNS float8
 	AS 'MODULE_PATHNAME', 'sparsevec_cosine_distance' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
 
+CREATE FUNCTION l1_distance(sparsevec, sparsevec) RETURNS float8
+	AS 'MODULE_PATHNAME', 'sparsevec_l1_distance' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
+
 CREATE FUNCTION l2_norm(sparsevec) RETURNS float8
 	AS 'MODULE_PATHNAME', 'sparsevec_l2_norm' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
 
diff --git a/sql/vector.sql b/sql/vector.sql
index 69c3fc0..efa53b6 100644
--- a/sql/vector.sql
+++ b/sql/vector.sql
@@ -653,6 +653,9 @@ CREATE FUNCTION inner_product(sparsevec, sparsevec) RETURNS float8
 CREATE FUNCTION cosine_distance(sparsevec, sparsevec) RETURNS float8
 	AS 'MODULE_PATHNAME', 'sparsevec_cosine_distance' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
 
+CREATE FUNCTION l1_distance(sparsevec, sparsevec) RETURNS float8
+	AS 'MODULE_PATHNAME', 'sparsevec_l1_distance' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
+
 CREATE FUNCTION l2_norm(sparsevec) RETURNS float8
 	AS 'MODULE_PATHNAME', 'sparsevec_l2_norm' LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
 
diff --git a/src/sparsevec.c b/src/sparsevec.c
index 407195d..6ebdfba 100644
--- a/src/sparsevec.c
+++ b/src/sparsevec.c
@@ -781,6 +781,55 @@ sparsevec_cosine_distance(PG_FUNCTION_ARGS)
 	PG_RETURN_FLOAT8(1.0 - similarity);
 }
 
+/*
+ * Get the L1 distance between two sparse vectors
+ */
+PGDLLEXPORT PG_FUNCTION_INFO_V1(sparsevec_l1_distance);
+Datum
+sparsevec_l1_distance(PG_FUNCTION_ARGS)
+{
+	SparseVector *a = PG_GETARG_SPARSEVEC_P(0);
+	SparseVector *b = PG_GETARG_SPARSEVEC_P(1);
+	float	   *ax = SPARSEVEC_VALUES(a);
+	float	   *bx = SPARSEVEC_VALUES(b);
+	double		distance = 0.0;
+	int			bpos = 0;
+
+	CheckDims(a, b);
+
+	for (int i = 0; i < a->nnz; i++)
+	{
+		int			ai = a->indices[i];
+		int			bi = -1;
+
+		for (int j = bpos; j < b->nnz; j++)
+		{
+			bi = b->indices[j];
+
+			if (ai == bi)
+				distance += fabs(ax[i] - bx[j]);
+			else if (ai > bi)
+				distance += fabs(bx[j]);
+
+			/* Update start for next iteration */
+			if (ai >= bi)
+				bpos = j + 1;
+
+			/* Found or passed it */
+			if (bi >= ai)
+				break;
+		}
+
+		if (ai != bi)
+			distance += fabs(ax[i]);
+	}
+
+	for (int j = bpos; j < b->nnz; j++)
+		distance += fabs(bx[j]);
+
+	PG_RETURN_FLOAT8(distance);
+}
+
 /*
  * Get the L2 norm of a sparse vector
  */
diff --git a/test/expected/sparsevec_functions.out b/test/expected/sparsevec_functions.out
index 8f3dab6..96205ce 100644
--- a/test/expected/sparsevec_functions.out
+++ b/test/expected/sparsevec_functions.out
@@ -198,3 +198,23 @@ SELECT cosine_distance('{}/1'::sparsevec, '{}/1');
 
 SELECT cosine_distance('{1:2}/2'::sparsevec, '{1:1}/3');
 ERROR:  different sparsevec dimensions 2 and 3
+SELECT l1_distance('{}/2'::sparsevec, '{1:3,2:4}/2');
+ l1_distance 
+-------------
+           7
+(1 row)
+
+SELECT l1_distance('{}/2'::sparsevec, '{2:1}/2');
+ l1_distance 
+-------------
+           1
+(1 row)
+
+SELECT l1_distance('{1:1,2:2}/2'::sparsevec, '{1:3}/1');
+ERROR:  different sparsevec dimensions 2 and 1
+SELECT l1_distance('{1:3e38}/1'::sparsevec, '{1:-3e38}/1');
+ l1_distance 
+-------------
+    Infinity
+(1 row)
+
diff --git a/test/sql/sparsevec_functions.sql b/test/sql/sparsevec_functions.sql
index 76549c7..a1e6e42 100644
--- a/test/sql/sparsevec_functions.sql
+++ b/test/sql/sparsevec_functions.sql
@@ -37,3 +37,8 @@ SELECT cosine_distance('{1:1,2:1}/2'::sparsevec, '{1:-1,2:-1}/2');
 SELECT cosine_distance('{1:2}/2'::sparsevec, '{2:2}/2');
 SELECT cosine_distance('{}/1'::sparsevec, '{}/1');
 SELECT cosine_distance('{1:2}/2'::sparsevec, '{1:1}/3');
+
+SELECT l1_distance('{}/2'::sparsevec, '{1:3,2:4}/2');
+SELECT l1_distance('{}/2'::sparsevec, '{2:1}/2');
+SELECT l1_distance('{1:1,2:2}/2'::sparsevec, '{1:3}/1');
+SELECT l1_distance('{1:3e38}/1'::sparsevec, '{1:-3e38}/1');