How to change position of grid.draw

Question

I am arranging plots generated by ggplot2. I have to use print to print out plots and grid.draw to display legend.

Sample Code:

p0 <- ggplot(data = iris, geom = 'blank',
         aes(y = Petal.Width, x = Petal.Length, color = Species)) + geom_point() +
      theme(axis.title.x = element_blank(),
            axis.title.y = element_blank(),
            legend.position = "none")

p1 <- ggplot(data = iris, geom = 'blank',
         aes(y = Petal.Length, x = Petal.Width, color = Species)) + geom_point() +
       theme(axis.title.x = element_blank(),
             axis.title.y = element_blank(),
             legend.position = "none")

g_legend <- function(a.gplot){
  tmp <- ggplot_gtable(ggplot_build(a.gplot))
  leg <- which(sapply(tmp$grobs, function(x) x$name) == "guide-box")
  legend <- tmp$grobs[[leg]]
  return(legend)
}

p <- ggplot(data = iris, geom = 'blank',
        aes(y = Petal.Width, x = Petal.Length, color = Species)) + geom_point()


grid.newpage() 
pushViewport(viewport(layout = grid.layout(2, 4)))
print(p0,vp = viewport(layout.pos.row = 1, layout.pos.col = 1))
print(p0,vp = viewport(layout.pos.row = 1, layout.pos.col = 2:3))
print(p1,vp = viewport(layout.pos.row = 2, layout.pos.col = 2:3))
grid.text("This is x label",gp=gpar(fontsize = 14), vjust = 11,
          vp = viewport(layout.pos.row = 2, layout.pos.col = 2))
grid.text("This is y label",gp=gpar(fontsize = 14), vjust = -11, rot = 90,
          ![enter image description here][1]vp = viewport(layout.pos.row = 2, layout.pos.col = 2))

grid.draw(g_legend(p))

I would like to put the legend at the fourth column. How can I do it? Thanks.

Answer 1

using gridExtra

         library(gridExtra)
         grid.arrange(p0 , p1,  g_legend(p), ncol=3,
         heights=c(10, 1),widths =c(1,2,1) ,as.table =TRUE)

Answer 2

You can manually change the x and y coordinates in the TableGrob object. For example, you could do the following to position the legend in the center of the plot:

leg <- g_legend(p)
leg$vp$x <- unit(.5, 'npc')
leg$vp$y <- unit(.5, 'npc')

When you call grid.draw(leg), it will be positioned in the center. Use different values to put it wherever you like.