tokens_replace {quanteda}

Replace tokens in a tokens object

Description

Substitute token types based on vectorized one-to-one matching. Since this function is created for lemmatization or user-defined stemming. It supports substitution of multi-word features by multi-word features, but substitution is fastest when pattern and replacement are character vectors and valuetype = "fixed" as the function only substitute types of tokens. Please use tokens_lookup() with exclusive = FALSE to replace dictionary values.

Usage

tokens_replace(
  x,
  pattern,
  replacement,
  valuetype = "glob",
  case_insensitive = TRUE,
  apply_if = NULL,
  verbose = quanteda_options("verbose")
)

Arguments

x

tokens object whose token elements will be replaced

pattern

a character vector or list of character vectors. See pattern for more details.

replacement

a character vector or (if pattern is a list) list of character vectors of the same length as pattern

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.

case_insensitive

logical; if TRUE, ignore case when matching a pattern or dictionary values

apply_if

logical vector of length ndoc(x); documents are modified only when corresponding values are TRUE, others are left unchanged.

verbose

print status messages if TRUE

See Also

tokens_lookup

Examples

toks1 <- tokens(data_corpus_inaugural, remove_punct = TRUE)

# lemmatization
taxwords <- c("tax", "taxing", "taxed", "taxed", "taxation")
lemma <- rep("TAX", length(taxwords))
toks2 <- tokens_replace(toks1, taxwords, lemma, valuetype = "fixed")
kwic(toks2, "TAX") |>
    tail(10)

# stemming
type <- types(toks1)
stem <- char_wordstem(type, "porter")
toks3 <- tokens_replace(toks1, type, stem, valuetype = "fixed", case_insensitive = FALSE)
identical(toks3, tokens_wordstem(toks1, "porter"))

# multi-multi substitution
toks4 <- tokens_replace(toks1, phrase(c("Supreme Court")),
                        phrase(c("Supreme Court of the United States")))
kwic(toks4, phrase(c("Supreme Court of the United States")))