Adds a basic count-min sketch example for RedisBloom. (#1842)

Author: Simon Prickett

examples/README.md

@@ -8,6 +8,7 @@ This folder contains example scripts showing how to use Node Redis in different
 | `bloom-filter.js`           | Space efficient set membership checks with a [Bloom Filter](https://en.wikipedia.org/wiki/Bloom_filter) using [RedisBloom](https://redisbloom.io) |
 | `command-with-modifiers.js` | Define a script that allows to run a command with several modifiers                                                                               |
 | `connect-as-acl-user.js`    | Connect to Redis 6 using an ACL user                                                                                                              |
+| `count-min-sketch.js`       | Estimate the frequency of a given event using the [RedisBloom](https://redisbloom.io) Count-Min Sketch                                            |
 | `lua-multi-incr.js`         | Define a custom lua script that allows you to perform INCRBY on multiple keys                                                                     |
 | `managing-json.js`          | Store, retrieve and manipulate JSON data atomically with [RedisJSON](https://redisjson.io/)                                                       |
 | `search-hashes.js`          | Uses [RediSearch](https://redisearch.io) to index and search data in hashes                                                                       |

examples/count-min-sketch.js

@@ -0,0 +1,83 @@
+// This example demonstrates the use of the Count-Min Sketch
+// in the RedisBloom module (https://redisbloom.io/)
+
+import { createClient } from 'redis';
+
+async function countMinSketch() {
+  const client = createClient();
+
+  await client.connect();
+
+  // Delete any pre-existing Count-Min Sketch.
+  await client.del('mycms');
+
+  // Initialize a Count-Min Sketch with error rate and probability:
+  // https://oss.redis.com/redisbloom/CountMinSketch_Commands/#cmsinitbyprob
+  try {
+    await client.cms.initByProb('mycms', 0.001, 0.01);
+    console.log('Reserved Top K.');
+  } catch (e) {
+    console.log('Error, maybe RedisBloom is not installed?:');
+    console.log(e);
+  }
+
+  const teamMembers = [
+    'leibale',
+    'simon',
+    'guy',
+    'suze',
+    'brian',
+    'steve',
+    'kyleb',
+    'kyleo',
+    'josefin',
+    'alex',
+    'nava',
+    'lance',
+    'rachel',
+    'kaitlyn'
+  ];
+
+  // Store actual counts for comparison with CMS.
+  let actualCounts = {};
+
+  // Randomly emit a team member and count them with the CMS.
+  for (let n = 0; n < 1000; n++) {
+    const teamMember = teamMembers[Math.floor(Math.random() * teamMembers.length)];
+    await client.cms.incrBy('mycms', {
+      item: teamMember,
+      incrementBy: 1
+    });
+
+    actualCounts[teamMember] = actualCounts[teamMember] ? actualCounts[teamMember] + 1 : 1;
+
+    console.log(`Incremented score for ${teamMember}.`);
+  }
+
+  // Get count estimate for some team members:
+  // https://oss.redis.com/redisbloom/CountMinSketch_Commands/#cmsquery
+  const [ alexCount, rachelCount ] = await client.cms.query('mycms', [
+    'simon',
+    'lance'
+  ]);
+
+  console.log(`Count estimate for alex: ${alexCount} (actual ${actualCounts.alex}).`);
+  console.log(`Count estimate for rachel: ${rachelCount} (actual ${actualCounts.rachel}).`);
+
+  // Get overall information about the Count-Min Sketch:
+  // https://oss.redis.com/redisbloom/CountMinSketch_Commands/#cmsinfo
+  const info = await client.cms.info('mycms');
+  console.log('Count-Min Sketch info:');
+
+  // info looks like this:
+  // { 
+  //   width: 2000, 
+  //   depth: 7, 
+  //   count: 1000 
+  // }
+  console.log(info);
+  
+  await client.quit();
+}
+
+countMinSketch();