How to calculate per document probabilities under respective topics with BERTopics?

Question

I am trying to use BERTopic to analyze the topic distribution of documents, after BERTopic is performed, I would like to calculate the probabilities under respective topics per document, how should I did it?

# define model
model = BERTopic(verbose=True,
                 vectorizer_model=vectorizer_model,
                 embedding_model='paraphrase-MiniLM-L3-v2',
                 min_topic_size= 50,
                 nr_topics=10)

#  train model
headline_topics, _ = model.fit_transform(df1.review_processed3)

# examine one of the topic
a_topic = freq.iloc[0]["Topic"] # Select the 1st topic
model.get_topic(a_topic) # Show the words and their c-TF-IDF scores

Below is the words and their c-TF-IDF scores for one of the Topics image 1

How should I change the result into Topic Distribution as below in order to calculate the topic distribution score and also identify the main topic? image 2

Answer 1

First, to compute probabilities, you have to add to your model definition calculate_probabilities=True (this could slow down the extraction of topics if you have many documents, > 100000).

# define model
model = BERTopic(verbose=True,
                 vectorizer_model=vectorizer_model,
                 embedding_model='paraphrase-MiniLM-L3-v2',
                 min_topic_size= 50,
                 nr_topics=10,
                 calculate_probabilities=True)

Then, calling fit_transform, you should save the probabilities:

headline_topics, probs = model.fit_transform(df1.review_processed3)

Now, you can create a pandas dataframe which shows probabilities under respective topics per document.

import pandas as pd
probs_df=pd.DataFrame(probs)
probs_df['main percentage'] = pd.DataFrame({'max': probs_df.max(axis=1)})