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#' Stack overlapping objects on top of one another.
#'
#' @inheritParams position_identity
#' @family position adjustments
#' @export
#' @examples
#' # Stacking is the default behaviour for most area plots:
#' ggplot(mtcars, aes(factor(cyl), fill = factor(vs))) + geom_bar()
#'
#' # To change stacking order, use factor() to change order of levels
#' mtcars$vs <- factor(mtcars$vs, levels = c(1,0))
#' ggplot(mtcars, aes(factor(cyl), fill = factor(vs))) + geom_bar()
#'
#' ggplot(diamonds, aes(price)) + geom_histogram(binwidth=500)
#' ggplot(diamonds, aes(price, fill = cut)) + geom_histogram(binwidth=500)
#'
#' # Stacking is also useful for time series
#' data.set <- data.frame(
#' Time = c(rep(1, 4),rep(2, 4), rep(3, 4), rep(4, 4)),
#' Type = rep(c('a', 'b', 'c', 'd'), 4),
#' Value = rpois(16, 10)
#' )
#'
#' qplot(Time, Value, data = data.set, fill = Type, geom = "area")
#' # If you want to stack lines, you need to say so:
#' qplot(Time, Value, data = data.set, colour = Type, geom = "line")
#' qplot(Time, Value, data = data.set, colour = Type, geom = "line",
#' position = "stack")
#' # But realise that this makes it *much* harder to compare individual
#' # trends
position_stack <- function (width = NULL, height = NULL) {
PositionStack$new(width = width, height = height)
}
PositionStack <- proto(Position, {
objname <- "stack"
adjust <- function(., data) {
if (empty(data)) return(data.frame())
data <- remove_missing(data, FALSE,
c("x", "y", "ymin", "ymax", "xmin", "xmax"), name = "position_stack")
if (is.null(data$ymax) && is.null(data$y)) {
message("Missing y and ymax in position = 'stack'. ",
"Maybe you want position = 'identity'?")
return(data)
}
if (!is.null(data$ymin) && !all(data$ymin == 0))
warning("Stacking not well defined when ymin != 0", call. = FALSE)
collide(data, .$width, .$my_name(), pos_stack)
}
})
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