DOC-4838 added node-redis vector query example

content/develop/clients/nodejs/vecsearch.md

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+---
+categories:
+- docs
+- develop
+- stack
+- oss
+- rs
+- rc
+- oss
+- kubernetes
+- clients
+description: Learn how to index and query vector embeddings with Redis
+linkTitle: Index and query vectors
+title: Index and query vectors
+weight: 4
+---
+
+[Redis Query Engine]({{< relref "/develop/interact/search-and-query" >}})
+lets you index vector fields in [hash]({{< relref "/develop/data-types/hashes" >}})
+or [JSON]({{< relref "/develop/data-types/json" >}}) objects (see the
+[Vectors]({{< relref "/develop/interact/search-and-query/advanced-concepts/vectors" >}}) 
+reference page for more information).
+Among other things, vector fields can store *text embeddings*, which are AI-generated vector
+representations of the semantic information in pieces of text. The
+[vector distance]({{< relref "/develop/interact/search-and-query/advanced-concepts/vectors#distance-metrics" >}})
+between two embeddings indicates how similar they are semantically. By comparing the
+similarity of an embedding generated from some query text with embeddings stored in hash
+or JSON fields, Redis can retrieve documents that closely match the query in terms
+of their meaning.
+
+In the example below, we use the
+[`@xenova/transformers`](https://www.npmjs.com/package/@xenova/transformers)
+library to generate vector embeddings to store and index with
+Redis Query Engine.
+
+## Initialize
+
+Install [`node-redis`]({{< relref "/develop/clients/nodejs" >}}) if you
+have not already done so. Also, install `@xenova/transformers` with the
+following command:
+
+```bash
+npm install @xenova/transformers
+```
+
+In a new JavaScript source file, start by importing the required classes:
+
+```js
+import * as transformers from '@xenova/transformers';
+import {VectorAlgorithms, createClient, SchemaFieldTypes} from 'redis';
+```
+
+The first of these imports is the `@xenova/transformers` module, which handles
+the embedding models.
+Here, we use an instance of the
+[`all-distilroberta-v1`](https://huggingface.co/sentence-transformers/all-distilroberta-v1)
+model for the embeddings. This model generates vectors with 768 dimensions, regardless
+of the length of the input text, but note that the input is truncated to 128
+tokens (see
+[Word piece tokenization](https://huggingface.co/learn/nlp-course/en/chapter6/6)
+at the [Hugging Face](https://huggingface.co/) docs to learn more about the way tokens
+are related to the original text).
+
+The `pipe` value obtained here is a function that we can call to generate the
+embeddings. We also need an object to pass some options for the `pipe()` function
+call. These specify the way the sentence embedding is generated from individual
+token embeddings (see the
+[`all-distilroberta-v1`](https://huggingface.co/sentence-transformers/all-distilroberta-v1)
+docs for more information).
+
+```js
+let pipe = await transformers.pipeline(
+    'feature-extraction', 'Xenova/all-distilroberta-v1'
+);
+
+const pipeOptions = {
+    pooling: 'mean',
+    normalize: true,
+};
+```
+
+## Create the index
+
+Connect to Redis and delete any index previously created with the
+name `vector_idx`. (The `dropIndex()` call throws an exception if
+the index doesn't already exist, which is why you need the
+`try...catch` block.)
+
+```js
+const client = createClient({url: 'redis://localhost:6379'});
+
+await client.connect();
+
+try { await client.ft.dropIndex('vector_idx'); } catch {}
+```
+
+Next, create the index.
+The schema in the example below specifies hash objects for storage and includes
+three fields: the text content to index, a
+[tag]({{< relref "/develop/interact/search-and-query/advanced-concepts/tags" >}})
+field to represent the "genre" of the text, and the embedding vector generated from
+the original text content. The `embedding` field specifies
+[HNSW]({{< relref "/develop/interact/search-and-query/advanced-concepts/vectors#hnsw-index" >}}) 
+indexing, the
+[L2]({{< relref "/develop/interact/search-and-query/advanced-concepts/vectors#distance-metrics" >}})
+vector distance metric, `Float32` values to represent the vector's components,
+and 768 dimensions, as required by the `all-distilroberta-v1` embedding model.
+
+```js
+await client.ft.create('vector_idx', {
+    'content': {
+        type: SchemaFieldTypes.TEXT,
+    },
+    'genre': {
+        type:SchemaFieldTypes.TAG,
+    },
+    'embedding': {
+        type: SchemaFieldTypes.VECTOR,
+        TYPE: 'FLOAT32',
+        ALGORITHM: VectorAlgorithms.HNSW,
+        DISTANCE_METRIC: 'L2',
+        DIM: 768,
+    }
+},{
+    ON: 'HASH',
+    PREFIX: 'doc:'
+});
+```
+
+## Add data
+
+You can now supply the data objects, which will be indexed automatically
+when you add them with [`hSet()`]({{< relref "/commands/hset" >}}), as long as
+you use the `doc:` prefix specified in the index definition.
+
+Use the `pipe()` method and the `pipeOptions` object that we created earlier to
+generate the embedding that represents the `content` field.
+The object returned by `pipe()` includes a `data` attribute, which is a
+[`Float32Array`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float32Array)
+that contains the embedding data. If you are indexing hash objects, as
+we are here, then you must also call
+[`Buffer.from()`](https://nodejs.org/api/buffer.html#static-method-bufferfromarraybuffer-byteoffset-length)
+on this array's `buffer` value to convert the `Float32Array`
+to a binary string. If you are indexing JSON objects, you can just
+use the `Float32Array` directly to represent the embedding.
+
+Make the `hSet()` calls within a
+[`Promise.all()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/all)
+call to create a Redis [pipeline]({{< relref "/develop/use/pipelining" >}})
+(not to be confused with the `@xenova/transformers` pipeline).
+This combines the commands together into a batch to reduce network
+round trip time.
+
+```js
+const sentence1 = 'That is a very happy person';
+const doc1 = {
+    'content': sentence1, 
+    'genre':'persons', 
+    'embedding':Buffer.from(
+        (await pipe(sentence1, pipeOptions)).data.buffer
+    ),
+};
+
+const sentence2 = 'That is a happy dog';
+const doc2 = {
+    'content': sentence2, 
+    'genre':'pets', 
+    'embedding': Buffer.from(
+        (await pipe(sentence2, pipeOptions)).data.buffer
+    )
+};
+
+const sentence3 = 'Today is a sunny day';
+const doc3 = {
+    'content': sentence3, 
+    'genre':'weather', 
+    'embedding': Buffer.from(
+        (await pipe(sentence3, pipeOptions)).data.buffer
+    )
+};
+
+await Promise.all([
+    client.hSet('doc:1', doc1),
+    client.hSet('doc:2', doc2),
+    client.hSet('doc:3', doc3)
+]);
+```
+
+## Run a query
+
+After you have created the index and added the data, you are ready to run a query.
+To do this, you must create another embedding vector from your chosen query
+text. Redis calculates the vector distance between the query vector and each
+embedding vector in the index and then ranks the results in order of this
+distance value.
+
+The code below creates the query embedding using `pipe()`, as with
+the indexing, and passes it as a parameter during execution
+(see
+[Vector search]({{< relref "/develop/interact/search-and-query/query/vector-search" >}})
+for more information about using query parameters with embeddings).
+
+The query returns an array of objects representing the documents
+that were found (which are hash objects here). The `id` attribute
+contains the document's key. The `value` attribute contains an object
+with a key-value entry corresponding to each index field specified in the
+`RETURN` option of the query.
+
+
+```js
+const similar = await client.ft.search(
+    'vector_idx',
+    '*=>[KNN 3 @embedding $B AS score]',
+    {
+        'PARAMS': {
+            B: Buffer.from(
+                (await pipe('That is a happy person', pipeOptions)).data.buffer
+            ),
+        },
+        'RETURN': ['score', 'content'],
+        'DIALECT': '2'
+    },
+);
+
+for (const doc of similar.documents) {
+    console.log(`${doc.id}: '${doc.value.content}', Score: ${doc.value.score}`);
+}
+
+await client.quit();
+```
+
+The code is now ready to run, but note that it may take a while to download the
+`all-distilroberta-v1` model data the first time you run it. The
+code outputs the following results:
+
+```
+doc:1: 'That is a very happy person', Score: 0.127055495977
+doc:2: 'That is a happy dog', Score: 0.836842417717
+doc:3: 'Today is a sunny day', Score: 1.50889515877
+```
+
+The results are ordered according to the value of the `score`
+field, which represents the vector distance here. The lowest distance indicates
+the greatest similarity to the query.
+As you would expect, the result for `doc:1` with the content text
+*"That is a very happy person"*
+is the result that is most similar in meaning to the query text
+*"That is a happy person"*.
+
+## Learn more
+
+See
+[Vector search]({{< relref "/develop/interact/search-and-query/query/vector-search" >}})
+for more information about the indexing options, distance metrics, and query format
+for vectors.