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#' Get plot components
#'
#' Extract plot components from a ggplot or gtable. `get_plot_component()`
#' extracts grobs or a list of grobs. `plot_component_names()` provides the
#' names of the components in the plot. `plot_components()` returns all
#' components as a list.
#'
#' @param plot A ggplot or gtable to extract from.
#' @param pattern The name of the component.
#' @param return_all If there is more than one component, should all be returned
#' as a list? Default is `FALSE`.
#'
#' @return A grob or list of grobs (`get_plot_component()`, `plot_components()`)
#' or a character vector (`plot_component_names()`)
#' @examples
#' library(ggplot2)
#'
#' p <- ggplot(mpg, aes(displ, cty)) + geom_point()
#' ggdraw(get_plot_component(p, "ylab-l"))
#'
#' @export
get_plot_component <- function(plot, pattern, return_all = FALSE) {
plot <- as_gtable(plot)
grob_names <- plot_component_names(plot)
grobs <- plot_components(plot)
grobIndex <- which(grepl(pattern, grob_names))
if (length(grobIndex) != 0) {
if (length(grobIndex) > 1 && !return_all) {
# If there's more than one grob, return just the first one
warning("Multiple components found; returning the first one. To return all, use `return_all = TRUE`.")
grobIndex <- grobIndex[1]
matched_grobs <- grobs[[grobIndex]]
} else if (length(grobIndex) > 1 && return_all) {
# If there's more than one grob, return all as a list
matched_grobs <- grobs[grobIndex]
} else {
matched_grobs <- grobs[[grobIndex]]
}
}
# if there's no grob, return NULL
else {
matched_grobs <- NULL
}
invisible(matched_grobs)
}
#' @rdname get_plot_component
#' @export
plot_component_names <- function(plot) {
if (gtable::is.gtable(plot)) {
plot$layout$name
} else {
as_gtable(plot)$layout$name
}
}
#' @rdname get_plot_component
#' @export
plot_components <- function(plot) {
if (gtable::is.gtable(plot)) {
plot$grobs
} else {
as_gtable(plot)$grobs
}
}
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