R: Transformations on Corpora

tm_map {tm} | R Documentation

## Transformations on Corpora

### Description

Interface to apply transformation functions (also denoted as mappings) to corpora.

### Usage

    ## S3 method for class 'PCorpus'
    tm_map(x, FUN, ...)
    ## S3 method for class 'SimpleCorpus'
    tm_map(x, FUN, ...)
    ## S3 method for class 'VCorpus'
    tm_map(x, FUN, ..., lazy = FALSE)

### Arguments

`x` | A corpus.
`FUN` | a transformation function taking a text document (a character vector when `x` is a `SimpleCorpus`) as input and returning a text document (a character vector of the same length as the input vector for `SimpleCorpus`). The function `content_transformer` can be used to create a wrapper to get and set the content of text documents.
`...` | arguments to `FUN`.
`lazy` | a logical. Lazy mappings are mappings which are delayed until the content is accessed. It is useful for large corpora if only few documents will be accessed. In such a case it avoids the computationally expensive application of the mapping to all elements in the corpus.

### Value

A corpus with `FUN` applied to each document in `x`. In case of lazy mappings only internal flags are set. Access of individual documents triggers the execution of the corresponding transformation function.

### Note

Lazy transformations change R's standard evaluation semantics.

### See Also

`getTransformations` for available transformations.

### Examples

    data("crude")
    ## Document access triggers the stemming function
    ## (i.e., all other documents are not stemmed yet)
    tm_map(crude, stemDocument, lazy = TRUE)[[1]]
    ## Use wrapper to apply character processing function
    tm_map(crude, content_transformer(tolower))
    ## Generate a custom transformation function which takes the heading as new content
    headings <- function(x)
        PlainTextDocument(meta(x, "heading"),
                          id = meta(x, "id"),
                          language = meta(x, "language"))
    inspect(tm_map(crude, headings))

[Package tm version 0.7-5 Index]