Visualize LDA Topic Probabilities of Documents

This example shows how to visualize the topic probabilities of documents using a latent Dirichlet allocation (LDA) topic model.

A latent Dirichlet allocation (LDA) model is a topic model which discovers underlying topics in a collection of documents and infers word probabilities in topics. You can use an LDA model to transform documents into a vector of topic probabilities, also known as a topic mixture. You can visualize the LDA topics using stacked bar charts.

Load LDA Model

Load the LDA model factoryReportsLDAModel which is trained using a data set of factory reports detailing different failure events. For an example showing how to fit an LDA model to a collection of text data, see Analyze Text Data Using Topic Models.

load factoryReportsLDAModel
mdl

mdl = 
  ldaModel with properties:

                     NumTopics: 7
             WordConcentration: 1
            TopicConcentration: 0.5755
      CorpusTopicProbabilities: [0.1587 0.1573 0.1551 0.1534 0.1340 0.1322 0.1093]
    DocumentTopicProbabilities: [480×7 double]
        TopicWordProbabilities: [158×7 double]
                    Vocabulary: ["item"    "occasionally"    "get"    "stuck"    "scanner"    "spool"    "loud"    "rattling"    "sound"    "come"    "assembler"    "piston"    "cut"    "power"    "start"    "plant"    "capacitor"    "mixer"    …    ]
                    TopicOrder: 'initial-fit-probability'
                       FitInfo: [1×1 struct]

Visualize Topics Using Word Clouds

Visualize the topics using the wordcloud function.

numTopics = mdl.NumTopics;
figure
t = tiledlayout("flow");
title(t,"LDA Topics")
for i = 1:numTopics
    nexttile
    wordcloud(mdl,i);
    title("Topic " + i)
end

View Mixtures of Topics in Documents

Create an array of tokenized documents for a set of previously unseen documents using the same preprocessing function used when fitting the model.

The function preprocessText, listed in the Preprocessing Function section of the example, performs the following steps in order:

1. Tokenize the text using tokenizedDocument.

2. Lemmatize the words using normalizeWords.

3. Erase punctuation using erasePunctuation.

4. Remove a list of stop words (such as "and", "of", and "the") using removeStopWords.

5. Remove words with 2 or fewer characters using removeShortWords.

6. Remove words with 15 or more characters using removeLongWords.

Prepare the text data for analysis using the preprocessText function.

str = [
    "Coolant is pooling underneath assembler."
    "Sorter blows fuses at start up."
    "There are some very loud rattling sounds coming from the assembler."];
documents = preprocessText(str);

Transform the documents into vectors of topic probabilities using the transform function. Note that for very short documents, the topic mixtures may not be a strong representation of the document content.

topicMixtures = transform(mdl,documents);

Visualize the first topic mixture in a bar chart and label the bars using the top three words from each topic.

numTopics = mdl.NumTopics;
for i = 1:numTopics
    top = topkwords(mdl,3,i);
    topWords(i) = join(top.Word,", ");
end

figure
bar(categorical(topWords),topicMixtures(1,:))

xlabel("Topic")
ylabel("Probability")
title("Document Topic Probabilities")

To visualize the proportions of the topics in each document, or to visualize multiple topic mixtures, use a stacked bar chart.

figure
barh(topicMixtures,"stacked")

title("Topic Mixtures")
xlabel("Topic Probability")
ylabel("Document")

legend(topWords, ...
    Location="southoutside", ...
    NumColumns=2)

The regions of the stacked bar chart represent the proportion of the document belonging to the corresponding topic.

Preprocessing Function

The function preprocessText, performs the following steps in order:

1. Tokenize the text using tokenizedDocument.

2. Lemmatize the words using normalizeWords.

3. Erase punctuation using erasePunctuation.

4. Remove a list of stop words (such as "and", "of", and "the") using removeStopWords.

5. Remove words with 2 or fewer characters using removeShortWords.

6. Remove words with 15 or more characters using removeLongWords.

function documents = preprocessText(textData)

% Tokenize the text.
documents = tokenizedDocument(textData);

% Lemmatize the words.
documents = addPartOfSpeechDetails(documents);
documents = normalizeWords(documents,Style="lemma");

% Erase punctuation.
documents = erasePunctuation(documents);

% Remove a list of stop words.
documents = removeStopWords(documents);

% Remove words with 2 or fewer characters, and words with 15 or greater
% characters.
documents = removeShortWords(documents,2);
documents = removeLongWords(documents,15);

end