Semanlink - NLP girls and guys AND Text Similarity

First transform text units to vectors? not always (eg. sentence similarity task using lexical word alignment). But vectors are efficient to process, and benefit from existing clustering algorithms such as k-means.

Sentence level or document level? Sentence clustering to summarise large documents.

Thematic clustering vs Semantic clustering: depends on the similarity measure.

Text similarity measures:

- Cosine similarity of tf-idf (suitable to produce thematic clusters)
- Knowledge-based Measures (wordNet) (quantify semantic relatedness of words),
- Word embedings

Examples, sample code:

- using wordnet with NLTK, and the formula to compute sentence similarities from word similarities.
- computing similarities between docs using gensim/word2vec

Which clustering algorithm?

- when we have an approximation of the clusters number, and when the similarity measure is not expensive in terms of computation time, clustering algo are suitable and fast. Sample code of k-means clustering using tf-idf vectors with scikit-learn
- Hierarchical clustering algorithms
    - don't need to give the number of clusters
    - but time consuming (calculate a similarity matrix for the sentences) 
- for voluminous data, use an incremental clustering algorithm: sentences are processed one at a time ; each new sentence is compared to each of the already formed clusters.

2017-05-18 About