polmineR (version 0.8.8)

subset: Subsetting corpora and subcorpora

Description

The structural attributes of a corpus (s-attributes) can be used to generate subcorpora (i.e. a subcorpus class object) by applying the subset-method. To obtain a subcorpus, the subset-method can be applied on a corpus represented by a corpus object, a length-one character vector (as a shortcut), and on a subcorpus object.

Usage

# S4 method for corpus
subset(x, subset, regex = FALSE, ...)
# S4 method for character
subset(x, ...)
# S4 method for subcorpus
subset(x, subset, ...)
# S4 method for remote_corpus
subset(x, subset)

Value

A subcorpus object. If the expression provided by argument subset

includes undefined s-attributes, a warning is issued and the return value is NULL.

Arguments

x

A corpus or subcorpus object. A corpus may also specified by a length-one character vector.

subset

A logical expression indicating elements or rows to keep. The expression may be unevaluated (using quote or bquote).

regex

A logical value. If TRUE, values for s-attributes defined using the three dots (...) are interpreted as regular expressions and passed into a grep call for subsetting a table with the regions and values of structural attributes. If FALSE (the default), values for s-attributes must match exactly.

...

An expression that will be used to create a subcorpus from s-attributes.

See Also

The methods applicable for the subcorpus object resulting from subsetting a corpus or subcorpus are described in the documentation of the \link{subcorpus-class}. Note that the subset-method can also be applied to textstat-class objects (and objects inheriting from this class).

Examples

use("polmineR")

# examples for standard and non-standard evaluation
a <- corpus("GERMAPARLMINI")

# subsetting a corpus object using non-standard evaluation
sc <- subset(a, speaker == "Angela Dorothea Merkel")
sc <- subset(a, speaker == "Angela Dorothea Merkel" & date == "2009-10-28")
sc <- subset(a, grepl("Merkel", speaker))
sc <- subset(a, grepl("Merkel", speaker) & date == "2009-10-28")

# subsetting corpus specified by character vector
sc <- subset("GERMAPARLMINI", grepl("Merkel", speaker))
sc <- subset("GERMAPARLMINI", speaker == "Angela Dorothea Merkel")
sc <- subset("GERMAPARLMINI", speaker == "Angela Dorothea Merkel" & date == "2009-10-28")
sc <- subset("GERMAPARLMINI", grepl("Merkel", speaker) & date == "2009-10-28")

# subsetting a corpus using the (old) logic of the partition-method
sc <- subset(a, speaker = "Angela Dorothea Merkel")
sc <- subset(a, speaker = "Angela Dorothea Merkel", date = "2009-10-28")
sc <- subset(a, speaker = "Merkel", regex = TRUE)
sc <- subset(a, speaker = c("Merkel", "Kauder"), regex = TRUE)
sc <- subset(a, speaker = "Merkel", date = "2009-10-28", regex = TRUE)

# providing the value for s-attribute as a variable
who <- "Volker Kauder"
sc <- subset(a, quote(speaker == !!who))

# quoting and quosures necessary when programming against subset
# note how variable who needs to be handled
gparl <- corpus("GERMAPARLMINI")
subcorpora <- lapply(
  c("Angela Dorothea Merkel", "Volker Kauder", "Ronald Pofalla"),
  function(who) subset(gparl, speaker == !!who)
)