Replace features in dfm — dfm_replace • quanteda

Substitute features based on vectorized one-to-one matching for lemmatization or user-defined stemming.

dfm_replace(
  x,
  pattern,
  replacement,
  case_insensitive = TRUE,
  verbose = quanteda_options("verbose")
)

Arguments

x: dfm whose features will be replaced
pattern: a character vector. See pattern for more details.
replacement: if pattern is a character vector, then replacement must be character vector of equal length, for a 1:1 match.
case_insensitive: logical; if TRUE, ignore case when matching a pattern or dictionary values
verbose: if TRUE print the number of tokens and documents before and after the function is applied. The number of tokens does not include paddings.

Examples

dfmat1 <- dfm(tokens(data_corpus_inaugural))

# lemmatization
taxwords <- c("tax", "taxing", "taxed", "taxed", "taxation")
lemma <- rep("TAX", length(taxwords))
featnames(dfm_select(dfmat1, pattern = taxwords))
#> [1] "tax"      "taxation" "taxing"  
dfmat2 <- dfm_replace(dfmat1, pattern = taxwords, replacement = lemma)
featnames(dfm_select(dfmat2, pattern = taxwords))
#> [1] "TAX"

# stemming
feat <- featnames(dfmat1)
featstem <- char_wordstem(feat, "porter")
dfmat3 <- dfm_replace(dfmat1, pattern = feat, replacement = featstem, case_insensitive = FALSE)
identical(dfmat3, dfm_wordstem(dfmat1, "porter"))
#> [1] TRUE