tokens_compound: Convert token sequences into compound tokens

In quanteda: Quantitative Analysis of Textual Data

Convert token sequences into compound tokens

Description

Replace multi-token sequences with a multi-word, or "compound" token. The resulting compound tokens will represent a phrase or multi-word expression, concatenated with concatenator (by default, the "⁠_⁠" character) to form a single "token". This ensures that the sequences will be processed subsequently as single tokens, for instance in constructing a dfm.

Usage

tokens_compound(
  x,
  pattern,
  valuetype = c("glob", "regex", "fixed"),
  concatenator = concat(x),
  window = 0L,
  case_insensitive = TRUE,
  join = TRUE,
  keep_unigrams = FALSE,
  apply_if = NULL
)

Arguments

x	an input tokens object
pattern	a character vector, list of character vectors, dictionary, or collocations object. See pattern for details.
valuetype	the type of pattern matching: "glob" for "glob"-style wildcard expressions; "regex" for regular expressions; or "fixed" for exact matching. See valuetype for details.
concatenator	character; the concatenation character that will connect the tokens making up a multi-token sequence.
window	integer; a vector of length 1 or 2 that specifies size of the window of tokens adjacent to pattern that will be compounded with matches to pattern. The window can be asymmetric if two elements are specified, with the first giving the window size before pattern and the second the window size after. If paddings (empty "" tokens) are found, window will be shrunk to exclude them.
case_insensitive	logical; if TRUE, ignore case when matching a pattern or dictionary values
join	if TRUE, join overlapping compounds into a single compound; otherwise, form these separately. See examples.
keep_unigrams	if TRUE, keep the original tokens.
apply_if	logical vector of length ndoc(x); documents are modified only when corresponding values are TRUE, others are left unchanged.

Value

A tokens object in which the token sequences matching pattern have been replaced by new compounded "tokens" joined by the concatenator.

Note

Patterns to be compounded (naturally) consist of multi-word sequences, and how these are expected in pattern is very specific. If the elements to be compounded are supplied as space-delimited elements of a character vector, wrap the vector in phrase(). If the elements to be compounded are separate elements of a character vector, supply it as a list where each list element is the sequence of character elements.

See the examples below.

Examples

txt <- "The United Kingdom is leaving the European Union."
toks <- tokens(txt, remove_punct = TRUE)

# character vector - not compounded
tokens_compound(toks, c("United", "Kingdom", "European", "Union"))

# elements separated by spaces - not compounded
tokens_compound(toks, c("United Kingdom", "European Union"))

# list of characters - is compounded
tokens_compound(toks, list(c("United", "Kingdom"), c("European", "Union")))

# elements separated by spaces, wrapped in phrase() - is compounded
tokens_compound(toks, phrase(c("United Kingdom", "European Union")))

# supplied as values in a dictionary (same as list) - is compounded
# (keys do not matter)
tokens_compound(toks, dictionary(list(key1 = "United Kingdom",
                                      key2 = "European Union")))
# pattern as dictionaries with glob matches
tokens_compound(toks, dictionary(list(key1 = c("U* K*"))), valuetype = "glob")

# note the differences caused by join = FALSE
compounds <- list(c("the", "European"), c("European", "Union"))
tokens_compound(toks, pattern = compounds, join = TRUE)
tokens_compound(toks, pattern = compounds, join = FALSE)

# use window to form ngrams
tokens_remove(toks, pattern = stopwords("en")) |>
    tokens_compound(pattern = "leav*", join = FALSE, window = c(0, 3))

quanteda documentation built on Sept. 11, 2024, 6:08 p.m.