TermDocumentMatrix {tm}

Term-Document Matrix

Description

Constructs or coerces to a term-document matrix or a document-term matrix.

Usage

TermDocumentMatrix(x, control = list())
DocumentTermMatrix(x, control = list())
as.TermDocumentMatrix(x, ...)
as.DocumentTermMatrix(x, ...)

Arguments

x

for the constructors, a corpus or an R object from which a corpus can be generated via Corpus(VectorSource(x)); for the coercing functions, either a term-document matrix or a document-term matrix or a simple triplet matrix (package slam) or a term frequency vector.

control

a named list of control options. There are local options which are evaluated for each document and global options which are evaluated once for the constructed matrix. Available local options are documented in termFreq and are internally delegated to a termFreq call.

This is different for a SimpleCorpus. In this case all options are processed in a fixed order in one pass to improve performance. It always uses the Boost (https://www.boost.org) Tokenizer (via Rcpp) and takes no custom functions as option arguments.

Available global options are:

bounds

A list with a tag global whose value must be an integer vector of length 2. Terms that appear in less documents than the lower bound bounds$global[1] or in more documents than the upper bound bounds$global[2] are discarded. Defaults to list(global = c(1, Inf)) (i.e., every term will be used).

weighting

A weighting function capable of handling a TermDocumentMatrix. It defaults to weightTf for term frequency weighting. Available weighting functions shipped with the tm package are weightTf, weightTfIdf, weightBin, and weightSMART.

...

the additional argument weighting (typically a WeightFunction) is allowed when coercing a simple triplet matrix to a term-document or document-term matrix.

Value

An object of class TermDocumentMatrix or class DocumentTermMatrix (both inheriting from a simple triplet matrix in package slam) containing a sparse term-document matrix or document-term matrix. The attribute weighting contains the weighting applied to the matrix.

See Also

termFreq for available local control options.

Examples

data("crude")
tdm <- TermDocumentMatrix(crude,
                          control = list(removePunctuation = TRUE,
                                         stopwords = TRUE))
dtm <- DocumentTermMatrix(crude,
                          control = list(weighting =
                                         function(x)
                                         weightTfIdf(x, normalize =
                                                     FALSE),
                                         stopwords = TRUE))
inspect(tdm[202:205, 1:5])
inspect(tdm[c("price", "prices", "texas"), c("127", "144", "191", "194")])
inspect(dtm[1:5, 273:276])

s <- SimpleCorpus(VectorSource(unlist(lapply(crude, as.character))))
m <- TermDocumentMatrix(s,
                        control = list(removeNumbers = TRUE,
                                       stopwords = TRUE,
                                       stemming = TRUE))
inspect(m[c("price", "texa"), c("127", "144", "191", "194")])