In the previous chapter you learned how to use embeddings to analyze text. In this one, you'll learn an application of embeddings, which is semantic search. You've already learned semantic search in Module 2, so please feel free to take a look if you need a refresher!

In this chapter, using embeddings, similarity, and nearest neighbors, you'll create a search model that will look for the answer to the given query in the dataset.

This chapter comes with a corresponding codelab, and we encourage you to follow it along as you read the chapter.

For the setup, please refer to the Setting Up chapter at the beginning of this module.

The first example is semantic search. There was a time when web search engines relied on keywords to match your search queries to the most relevant sites. But these days, you would be one frustrated user if that’s the kind experience you get, because these search engines are now able to capture semantic understanding of what you are looking for, beyond just keyword-matching.

Let’s build a simple semantic search engine. For this chapter we'll use the same dataset as in the previous one, consisting of 50 top web search terms about Hello, World! taken from a keyword tool. The following are a few examples:

df = pd.read_csv("hello-world-kw.csv", names=["search_term"])
df.head()

Let’s pretend that these search terms make up an FAQ database. Our job now, given a new query, is to ensure that the search engine returns the most similar FAQs.

Recall that the Embed endpoint is quite straightforward to use:

• Prepare input — The input is the list of text you want to embed.
• Define model settings — The model setting is just one: the model type. But it does make a difference to your task because bigger models generate embeddings with higher dimensions. We’ll use the default which is large.
• Generate output — The output is the corresponding embeddings for the input text.

The code looks like this:

def embed_text(texts):
  output = co.embed(
                model="large",
                texts=texts)
  embedding = output.embeddings

  return embedding

Now, given the FAQs, let’s try the search term “what is the history of hello world.” This is a search term whose keyword (i.e., “history”) doesn’t exist at all in the FAQ. Let’s see how the search fares.

First we get the embeddings of all the FAQs:

df["search_term_embeds"] = embed_text(df["search_term"].tolist())
embeds = np.array(df["search_term_embeds"].tolist())

And then get the embeddings of the new query:

new_query = "what is the history of hello world"
new_query_embeds = embed_text(new_query)

Next, we compare the similarity of the embeddings of the new query with each of the embeddings of the FAQs. There are many options to do this, and one option is using cosine similarity. We’ll utilize scikit-learn’s library to perform this.

The steps are:

• Calculate similarity between the new query with each of the FAQs
• Sort the FAQs by descending order in similarity (the most similar first)
• Show the top FAQs with the highest similarity to the new query

The code is shown below:

from sklearn.metrics.pairwise import cosine_similarity

def get_similarity(target,candidates):
  # Turn list into array
  candidates = np.array(candidates)
  target = np.expand_dims(np.array(target),axis=0)

  # Calculate cosine similarity
  sim = cosine_similarity(target,candidates)
  sim = np.squeeze(sim).tolist()

  # Sort by descending order in similarity
  sim = list(enumerate(sim))
  sim = sorted(sim, key=lambda x:x[1], reverse=True)

  # Return similarity scores
  return sim

similarity = get_similarity(new_query_embeds,embeds)

# Show the top 5 FAQs with the highest similarity to the new query
for idx,score in similarity[:5]:
  print(f"Similarity: {score:.2f};", df.iloc[idx]["search_term"])

And the output we get is:

New query:
what is the history of hello world 

Similar queries:
Similarity: 0.89; how did hello world originate
Similarity: 0.87; where did hello world come from
Similarity: 0.82; what is hello world
Similarity: 0.73; why is hello world so famous
Similarity: 0.70; why hello world

It works! Notice that the top terms are indeed the closest in meaning to the search term (about the history and origin of Hello, World!) even though they use different kinds of words.

In this chapter you learned how to use embeddings a very important language AI task: search.