#' combines multiple plots with shared legend
#'
#' from https://github.com/tidyverse/ggplot2/wiki/share-a-legend-between-two-ggplot2-graphs
#'
#' @return plots
#'
#' @param position bottom or right for legend placement
#' @param ncol how many columns
#' @param nrom how many rows, default 1
#'
#'
#' @examples
#' p1 <- ggplot2::ggplot(data.frame(x=c("A","B","C"),y=1:3), ggplot2::aes(x=x,y=y,colour=x)) + ggplot2::geom_point()
#' p2 <- ggplot2::ggplot(data.frame(x=c("A","B","C"),y=1:3), ggplot2::aes(x=x,y=y,colour=x)) + ggplot2::geom_point()
#' grid_arrange_shared_legend(p1, p2)
#'
#' @export
grid_arrange_shared_legend <- function(..., ncol = length(list(...)), nrow = 1, position = c("bottom", "right")) {
plots <- list(...)
position <- match.arg(position)
g <- ggplotGrob(plots[[1]] + theme(legend.position = position))$grobs
legend <- g[[which(sapply(g, function(x) x$name) == "guide-box")]]
lheight <- sum(legend$height)
lwidth <- sum(legend$width)
gl <- lapply(plots, function(x) x + theme(legend.position="none"))
gl <- c(gl, ncol = ncol, nrow = nrow)
combined <- switch(position,
"bottom" = gridExtra::arrangeGrob(do.call(gridExtra::arrangeGrob, gl),
legend,
ncol = 1,
heights = grid::unit.c(unit(1, "npc") - lheight, lheight)),
"right" = gridExtra::arrangeGrob(do.call(gridExtra::arrangeGrob, gl),
legend,
ncol = 2,
widths = grid::unit.c(unit(1, "npc") - lwidth, lwidth)))
grid.newpage()
grid.draw(combined)
# return gtable invisibly
invisible(combined)
}
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