R/textstat-methods.R

In quanteda.textstats: Textual Statistics for the Quantitative Analysis of Textual Data

# base methods --------------

# textstat_select ------------

#' Select rows of textstat objects by glob, regex or fixed patterns
#'
#' Users can subset output object of `textstat_collocations`,
#' `textstat_keyness` or `textstat_frequency` based on
#' `"glob"`, `"regex"` or `"fixed"` patterns using this method.
#' @param x a `textstat` object
#' @param pattern see [quanteda::pattern]
#' @param selection whether to `"keep"` or `"remove"` the rows that
#'   match the pattern
#' @inheritParams quanteda::valuetype
#' @keywords textstat internal
#' @export
#' @examples
#' library("quanteda")
#'
#' period <- ifelse(docvars(data_corpus_inaugural, "Year") < 1945, "pre-war", "post-war")
#' dfmat <- tokens(data_corpus_inaugural) %>%
#'     dfm() %>%
#'     dfm_group(groups = period)
#' tstat <- textstat_keyness(dfmat)
#' textstat_select(tstat, 'america*')
#'
textstat_select <- function(x,
                            pattern = NULL,
                            selection = c("keep", "remove"),
                            valuetype = c("glob", "regex", "fixed"),
                            case_insensitive = TRUE) {
    UseMethod("textstat_select")
}

#' @export
textstat_select.default <- function(x, pattern = NULL,
                                  selection = c("keep", "remove"),
                                  valuetype = c("glob", "regex", "fixed"),
                                  case_insensitive = TRUE) {
    stop(friendly_class_undefined_message(class(x), "textstat_select"))
}

#' @export
textstat_select.textstat <- function(x, pattern = NULL,
                                     selection = c("keep", "remove"),
                                     valuetype = c("glob", "regex", "fixed"),
                                     case_insensitive = TRUE) {

    if (is.null(pattern)) return(x)
    selection <- match.arg(selection)
    valuetype <- match.arg(valuetype)
    attrs <- attributes(x)

    id <- unlist(pattern2id(pattern, x[[1]], valuetype, case_insensitive))
    if (selection == "keep") {
        x <- x[id, ]
    } else {
        x <- x[id * -1, ]
    }
    class(x) <- attrs$class
    return(x)
}