tm_map | R Documentation |
Interface to apply transformation functions (also denoted as mappings) to corpora.
## 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)
x |
A corpus. |
FUN |
a transformation function taking a text document (a character
vector when |
... |
arguments to |
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. |
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.
Lazy transformations change R's standard evaluation semantics.
getTransformations
for available transformations.
data("crude")
## Document access triggers the stemming function
## (i.e., all other documents are not stemmed yet)
if(requireNamespace("SnowballC")) {
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))
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