Added Morgan fingerprint example [skip ci]

Author: ankane

README.md

@@ -35,6 +35,7 @@ Or check out some examples:
 - [Binary embeddings](examples/cohere/example.js) with Cohere
 - [Sentence embeddings](examples/transformers/example.js) with Transformers.js
 - [Hybrid search](examples/hybrid-search/example.js) with Transformers.js
+- [Morgan fingerprints](examples/rdkit/example.js) with RDKit.js
 - [Recommendations](examples/disco/example.js) with Disco
 - [Horizontal scaling](examples/citus/example.js) with Citus
 - [Bulk loading](examples/loading/example.js) with `COPY`

examples/rdkit/example.js

@@ -0,0 +1,34 @@
+import pg from 'pg';
+import pgvector from 'pgvector/pg';
+import initRDKitModule from '@rdkit/rdkit';
+
+const RDKit = await initRDKitModule();
+
+function generateFingerprint(molecule) {
+  const options = {radius: 3};
+  return RDKit.get_mol(molecule).get_morgan_fp(JSON.stringify(options));
+}
+
+const client = new pg.Client({database: 'pgvector_example'});
+await client.connect();
+
+await client.query('CREATE EXTENSION IF NOT EXISTS vector');
+await pgvector.registerTypes(client);
+
+await client.query('DROP TABLE IF EXISTS molecules');
+await client.query('CREATE TABLE molecules (id text PRIMARY KEY, fingerprint bit(2048))');
+
+const molecules = ['Cc1ccccc1', 'Cc1ncccc1', 'c1ccccn1'];
+for (const molecule of molecules) {
+  const fingerprint = generateFingerprint(molecule);
+  await client.query('INSERT INTO molecules (id, fingerprint) VALUES ($1, $2)', [molecule, fingerprint]);
+}
+
+const queryMolecule = 'c1ccco1';
+const queryFingerprint = generateFingerprint(queryMolecule);
+const { rows } = await client.query('SELECT id, fingerprint <%> $1 AS distance FROM molecules ORDER BY distance LIMIT 5', [queryFingerprint]);
+for (let row of rows) {
+  console.log(row);
+}
+
+await client.end();

examples/rdkit/package.json

@@ -0,0 +1,9 @@
+{
+    "private": true,
+    "type": "module",
+    "dependencies": {
+        "@rdkit/rdkit": "^2023.9.2-1.0.0",
+        "pg": "^8.11.3",
+        "pgvector": "file:../.."
+    }
+}