R/expandRows.R

In splitstackshape: Stack and Reshape Datasets After Splitting Concatenated Values

#' Expand the Rows of a Dataset
#' 
#' Expands (replicates) the rows of a `data.frame` or `data.table`, either by a 
#' fixed number, a specified vector, or a value contained in one of the columns 
#' in the source `data.frame` or `data.table`.
#' 
#' 
#' @param dataset The input `data.frame` or `data.table`.
#' @param count The numeric vector of counts OR the column from the
#' dataset that contains the count data. If `count` is a single
#' digit, it is assumed that all rows should be repeated by this amount.
#' @param count.is.col Logical. Is the `count` value a column from the
#' input dataset? Defaults to `TRUE`.
#' @param drop Logical. If `count.is.col = TRUE`, should the "count"
#' column be dropped from the result? Defaults to `TRUE`.
#' @return A `data.frame` or `data.table`, depending on the input.
#' @author Ananda Mahto
#' @references \url{http://stackoverflow.com/a/19519828/1270695}
#' @examples
#' 
#' mydf <- data.frame(x = c("a", "b", "q"), 
#'                    y = c("c", "d", "r"), 
#'                    count = c(2, 5, 3))
#' library(data.table)
#' DT <- as.data.table(mydf)
#' mydf
#' expandRows(mydf, "count")
#' expandRows(DT, "count", drop = FALSE)
#' expandRows(mydf, count = 3) ## This takes values from the third column!
#' expandRows(mydf, count = 3, count.is.col = FALSE)
#' expandRows(mydf, count = c(1, 5, 9), count.is.col = FALSE)
#' expandRows(DT, count = c(1, 5, 9), count.is.col = FALSE)
#' 
#' @export expandRows
expandRows <- function(dataset, count, count.is.col = TRUE, drop = TRUE) {
  if (isTRUE(count.is.col)) {
    vals <- dataset[[count]]
    out <- dataset[rep(sequence(nrow(dataset)), vals), ]
    if (isTRUE(drop)) out[[count]] <- NULL
  } else if (length(count) == 1) {
    vals <- count
    out <- dataset[rep(sequence(nrow(dataset)), each = vals), ]
  } else {
    vals <- count
    out <- dataset[rep(sequence(nrow(dataset)), vals), ]
  }
  if (any(vals == 0)) {
    mess <- sprintf("The following rows have been dropped from the input: \n\n%s\n", 
                    paste(which(vals == 0), collapse = ", "))
    message(mess)
  }
  out
}
NULL