spelling

A Machine-Learning project for detection of langage and spelling correction.

How it works

A misspelled word can be considered as the observation of the real word that was meant to be written. Thus, correcting a spelling mistake is a classification problem of finding the correct class among all the existing words of a language. In this project, a Naive Bayes Classifier has been implemented.

Here's how it works: if,

• m is the word typed by the user
• c is a possible correction of this word
• P(c|m) is the probability that a user who typed m actually meant to type a correct word c instead

The Bayes Formula states that: P(c|m) = P(m|c)*P(c)/P(m)

We want to find c that maximizes P(c|m), so we can ignore P(m) (which is constant) and maximize P(m|c) and P(c).

• P(m|c) is the probability of making the mistake m by meaning to type c. It is the error model.
• P(c) is the probability that the user wanted to type c. It is the language model.

To model the typing errors, we use the editing distance d(m,c), which is the number of elementary operations (deletion, insetion, replacement or transposition of letters) needed to move from c to m. The error model can be written P(m|c) = Pe^d(m,c), with Pe a fixed error probability for mistyping one letter.

To model the probability of a given word to appear in a text, we can use pragmatic approach: the more this word appears in a large corpus, the greater its probability. The language model P(c) is the frequency of the word c in the corpus.

Finally, for any given typed word m, we generate a lot of potential correction canditates by generating errors of editing distance <= 2. Then, for each of this candidate words we compute the probability P(c|m) that they are the right correction, and we select the candidate with the highest probability.

The same approach can be used to determine the language of the sentence.

Corpus

I used the following corpus for training the language models.

French	English
Émile Zola, L'argent	William Shakespeare, Henry VI
Émile Zola, L'assommoir	William Shakespeare, Hamlet
Émile Zola, Germinal	William Shakespeare, MacBeth
Victor Hugo, Les Misérables	Lewis Caroll, Alice in Wonderland
Marcel Proust, Du côté de chez Swann	Sir Arthur Conan Doyle, Sherlock Holmes
Stendhal, Le rouge et le noir	Herman Melville, Moby Dick ; or The Whale
Alexandre Dumas, Les trois mousquetaires	Mary Shelley, Frankenstein or The Modern Prometheus
Gustave Flaubert, Madame Bovary	Charles Dickens, Great Expectations

Results

The performance of correction reaches about 83%.

A more detailed analysis can be found in the project report.