R/match_col_class.R

In toniprice/jute: Sundry Utility Functions

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#' Get column indexes of a given class in a data frame
#'
#' Given a specified class such as "numeric" or "character", gets the column
#' indexes in a data frame for columns matching that class.
#'
#' @param df The data frame for which columns should be matched.
#' @param class_type The type of class to match as a character string (e.g.
#'   "numeric", "integer", "logical", "character", "factor").
#'
#' @return A vector of column indexes corresponding to columns with classes that
#'   match the specified class.
#'
#' @examples
#' id <- letters[1:3]
#' size <- c(1.2, 3.5, 4.1)
#' num <- c(1, 2, 3)
#' intgr <- c(1L, 2L, 3L)
#'
#' df_no_fac <- data.frame(id, size, num, intgr, stringsAsFactors = FALSE)
#' match_col_class(df_no_fac, "character")
#'
#' df_with_fac <- data.frame(id, size, num, intgr)
#' match_col_class(df_with_fac, "character")
#' match_col_class(df_with_fac, "factor")
#' match_col_class(df_with_fac, "numeric")
#' match_col_class(df_with_fac, "integer")
#'
#' @export
#'
match_col_class <- function(df, class_type) {
  which(vapply(df, class, FUN.VALUE = character(1)) == class_type)
}

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