Controlling the plot layout when sharing legends b

Question

Here is a function to extract the legend from a ggplot2 object and use it as a own object in grid.arrange():

https://github.com/hadley/ggplot2/wiki/Share-a-legend-between-two-ggplot2-graphs

However, what i am really struggling with: I want the plots in only one row, but apparently the plot layout is not changeable. I believe that

grid_arrange_shared_legend <- function(...) {
    plots <- list(...)
    g <- ggplotGrob(plots[[1]] + theme(legend.position="bottom"))$grobs
    legend <- g[[which(sapply(g, function(x) x$name) == "guide-box")]]
    lheight <- sum(legend$height)
    grid.arrange(
        do.call(arrangeGrob, lapply(plots, function(x)
            x + theme(legend.position="none"))),
        legend,
        ncol = 1,
        heights = unit.c(unit(1, "npc") - lheight, lheight))
}

needs a nested grid.arrange command, as the ncol=1 argument is related to the legend. Is there a way to to do this?

Answer 1

here's a shorter alternative,

grid_arrange_shared_legend <- function(..., layout = rbind(c(1,2,3,4), 
                                                           c(5,5,5,5))) {
  plots <- list(...)
  g <- ggplotGrob(plots[[1]] + theme(legend.position="bottom"))$grobs
  legend <- g[[which(sapply(g, function(x) x$name) == "guide-box")]]
  lheight <- sum(legend$height)
  gl <- lapply(plots, function(x) x + theme(legend.position="none"))
  grid.arrange(grobs = c(gl, list(legend)), layout_matrix = layout,
    heights = grid::unit.c(unit(1, "npc") - lheight, lheight))
}

Answer 2

You can supply nrow = 1 as a list to do.call:

do.call(arrangeGrob, c(lapply(plots, function(x)
  x + theme(legend.position="none")), list(nrow = 1)))

I adapted the example from the link you provided:

library(ggplot2)
library(gridExtra)

grid_arrange_shared_legend <- function(...) {
  plots <- list(...)
  g <- ggplotGrob(plots[[1]] + theme(legend.position="bottom"))$grobs
  legend <- g[[which(sapply(g, function(x) x$name) == "guide-box")]]
  lheight <- sum(legend$height)
  grid.arrange(
    do.call(arrangeGrob, c(lapply(plots, function(x)
      x + theme(legend.position="none")), list(nrow = 1))),
    legend,
    ncol = 1,
    heights = grid::unit.c(unit(1, "npc") - lheight, lheight))
}

dsamp <- diamonds[sample(nrow(diamonds), 1000), ]
p1 <- qplot(carat, price, data=dsamp, colour=clarity)
p2 <- qplot(cut, price, data=dsamp, colour=clarity)
p3 <- qplot(color, price, data=dsamp, colour=clarity)
p4 <- qplot(depth, price, data=dsamp, colour=clarity)
grid_arrange_shared_legend(p1, p2, p3, p4)