This CRAN task view contains a list of packages useful for natural language processing.

Side-note on text mining: In recent years, we have elaborated a framework to be used in packages dealing with the processing of written material: the package tm. Extension packages in this area are highly recommended to interface with tm's basic routines and developers are cordially invited to join in the discussion on further developments of this framework package.

Lexical Databases:

• wordnet provides an R interface to WordNet , a large lexical database of English.

Keyword Extraction and General String Manipulation:

• R's base package already provides a rich set of character manipulation routines. See help.search(keyword = "character", package = "base") for more information on these capabilities.
• RKEA provides an R interface to KEA (Version 5.0). KEA (for Keyphrase Extraction Algorithm) allows for extracting keyphrases from text documents. It can be either used for free indexing or for indexing with a controlled vocabulary.
• gsubfn can be used for certain parsing tasks such as extracting words from strings by content rather than by delimiters. demo("gsubfn-gries") shows an example of this in a natural language processing context.
• tau contains basic string manipulation and analysis routines needed in text processing such as dealing with character encoding, language, pattern counting, and tokenization.

Natural Language Processing:

• openNLP provides an R interface to OpenNLP , a collection of natural language processing tools including a sentence detector, tokenizer, pos-tagger, shallow and full syntactic parser, and named-entity detector, using the Maxent Java package for training and using maximum entropy models.
• openNLPmodels.en ships trained models for English and openNLPmodels.es for Spanish to be used with openNLP.
• RWeka is a interface to Weka which is a collection of machine learning algorithms for data mining tasks written in Java. Especially useful in the context of natural language processing is its functionality for tokenization and stemming.
• Snowball provides the Snowball stemmers which contain the Porter stemmer and several other stemmers for different languages. See the Snowball webpage for details.
• Rstem (available from Omegahat) is an alternative interface to a C version of Porter's word stemming algorithm.
• KoNLP provides a collection of conversion routines (e.g. Hangul to Jamos), stemming, and part of speech tagging through interfacing with the Lucene's HanNanum analyzer. In version 0.0-8.0, the documentation is sparse and still needs some help.

String Kernels:

• kernlab allows to create and compute with string kernels, like full string, spectrum, or bounded range string kernels. It can directly use the document format used by tm as input.

Text Mining:

• tm provides a comprehensive text mining framework for R. The Journal of Statistical Software article Text Mining Infrastructure in R gives a detailed overview and presents techniques for count-based analysis methods, text clustering, text classification and string kernels.
• lsa provides routines for performing a latent semantic analysis with R. The basic idea of latent semantic analysis (LSA) is, that text do have a higher order (=latent semantic) structure which, however, is obscured by word usage (e.g. through the use of synonyms or polysemy). By using conceptual indices that are derived statistically via a truncated singular value decomposition (a two-mode factor analysis) over a given document-term matrix, this variability problem can be overcome. The article Investigating Unstructured Texts with Latent Semantic Analysis gives a detailed overview and demonstrates the use of the package with examples from the are of technology-enhanced learning.
• topicmodels provides an interface to the C code for Latent Dirichlet Allocation (LDA) models and Correlated Topics Models (CTM) by David M. Blei and co-authors and the C++ code for fitting LDA models using Gibbs sampling by Xuan-Hieu Phan and co-authors.
• koRpus is a diverse collection of functions for automatic language detection, hyphenation, several indices of lexical diversity (e.g., type token ratio, HD-D/vocd-D, MTLD) and readability (e.g., Flesch, SMOG, LIX, Dale-Chall). See the web page for more information.
• RTextTools is a machine learning package for automatic text classification. It implements the nine different algorithms (svm, slda, boosting, bagging, rf, glmnet, tree, nnet, and maxent) and routines supporting the evaluation of accuracy.
• textir is a suite of tools for text and sentiment mining.
• textcat provides support for n-gram based text categorization.
• corpora offers utility functions for the statistical analysis of corpus frequency data.
• languageR provides data sets and functions exemplifying statistical methods, and some facilitatory utility functions used in the book by R. H. Baayen: "Analyzing Linguistic Data: a Practical Introduction to Statistics Using R", Cambridge University Press, 2008.
• zipfR offers some statistical models for word frequency distributions. The utilities include functions for loading, manipulating and visualizing word frequency data and vocabulary growth curves. The package also implements several statistical models for the distribution of word frequencies in a population. (The name of this library derives from the most famous word frequency distribution, Zipf's law.)
• maxent is an implementation of maxinum entropy minimising memory consumption of very large data-sets.
• TextRegression predict valued outputs based on an input matrix and assess predictive power ('the bag-of-words oracle').
• wordcloud provides a visualisation similar to the famous wordle ones: it horizontally and vertically distributes features in a pleasing visualisation with the font size scaled by frequency.

Import filters and Data Handling:

• tm.plugin.dc allows for distributing corpora across storage devices (local files or Hadoop Distributed File System).
• tm.plugin.mail helps with importing mail messages from archive files such as used in Thunderbird (mbox, eml).