strutopy: Python Implementation for the Structural Topic Model

The implementation in Python aims for computational efficiency as well as ease-of-use.

Structural Topic Model (Roberts et al. 2016) can be used to extend the former topic modelling approaches by including text metadata on a document level. The meta information can be introduced to the estimation procedure two-fold, via:

1. topical content covariates that shape the word usage within topics
2. topical prevalence covariates that shape the frequency of topic occurences.

Contribution of this thesis:

The contribution of this thesis is twofold:

1. A complete implementation of the STM model and estimation procedure is provided. The main module is contained in src/modules/stm.py
2. A comprehensive comparison between STM and its direct predecessor CTM is conducted using the implementation provided hereby.

Setup

In order to reproduce and use the code of the repository, the following steps are recommended:

Create and activate a new virtual environment (from the root of the repository):

python -m venv .venv

Activate the virtual environment:

source .venv/bin/activate

Install all python dependencies:

pip install -r requirements.txt

Quickstart

Navigate to the following folder:

cd src

And execute the python scripts in the following order:

1. To get the articles from wikipedia, run src/01_get_wiki_docs.py:

python 01_get_wiki_docs.py

2. To create the reference corpus, run src/02_create_corpus.py:

python 02_create_corpus.py

3. To fit the reference model for K=[10,...,70], run src/03_fit_reference_model.py:

python 03_fit_reference_model.py

4. To create the set of synthetic corpora for varying value of gamma, run src/04_create_synthetic_corpora.py:

python 04_create_synthetic_corpora.py

5. To train STM & CTM on the synthetic corpora, run src/05_train.py:

python 05_train.py

Training STM & CTM provides us with the simulation results obtained in this master thesis. The following example visualisation can be obtained:

6. To reproduce the application results, run src/06_example_application.py:

python 06_example_application.py

Repository Components

1. Corpus creation: A corpus in the Bag-of-Words format is required for STM. In addition, metadata is needed to play to the strengths of STM:

• list of documents containing word indices and their count
• vector of words associated with the indices
• metadata matrix with document covariates

2. Model Estimation (src/modules/stm.py)

• Spectral Initialisation
• Semi collapsed Laplace Approximation Variational Expectation-Maximization Algorithm
• Topical Prevalence Model
• Topical Content Model

3. Model Evaluation

• Label topics by retrieving the most relevant words per topic. Relevance is given in terms of:
  • Highest probability
  • FREX: harmonic mean for semantic coherence and exclusivity