ggplot2 dual axes

README.md

Dual axes for ggplot2

Modified from:

https://stackoverflow.com/questions/21026598/ggplot2-adding-secondary-transformed-x-axis-on-top-of-plot

https://rpubs.com/kohske/dual_axis_in_ggplot2

Updated: 2016-07-27

Example for x-axis

# Create fake data.frame
data.add.x = data.frame(
  y1 = runif(100, 0, 100),
  x1 = runif(100, 0, 100)
)

# Add second x-axis that scales with first
data.add.x$x2 = (data.add.x$x1 + 50)^0.75

# Create plots
plot1.x = qplot(y = y1, x = x1, data = data.add.x)
plot2.x = qplot(y = y1, x = x2, data = data.add.x)

# Run function
ggplot_dual_axis(plot1.x, plot2.x, "x")

Example for y-axis

# Add second y-axis that scales with first
data.add.x$y2 = (data.add.x$y^0.5) / 500

# Create plots
plot1.y = qplot(y = y1, x = x1, data = data.add.x)
plot2.y = qplot(y = y2, x = x1, data = data.add.x)

# Run function
ggplot_dual_axis(plot1.y, plot2.y, "y")

ggplot_dual_axis.R

ggplot_dual_axis = function(plot1, plot2, which.axis = "x") {
  
  # Update plot with transparent panel
  plot2 = plot2 + theme(panel.background = element_rect(fill = NA))
  
  grid.newpage()
  
  # Increase right margin if which.axis == "y"
  if(which.axis == "y") plot1 = plot1 + theme(plot.margin = unit(c(0.7, 1.5, 0.4, 0.4), "cm"))
  
  # Extract gtable
  g1 = ggplot_gtable(ggplot_build(plot1))
  
  g2 = ggplot_gtable(ggplot_build(plot2))
  
  # Overlap the panel of the second plot on that of the first
  pp = c(subset(g1$layout, name == "panel", se = t:r))
  
  g = gtable_add_grob(g1, g2$grobs[[which(g2$layout$name=="panel")]], pp$t, pp$l, pp$b, pp$l)

  # Steal axis from second plot and modify
  axis.lab = ifelse(which.axis == "x", "axis-b", "axis-l")
  
  ia = which(g2$layout$name == axis.lab)
  
  ga = g2$grobs[[ia]]
  
  ax = ga$children[[2]]
  
  # Switch position of ticks and labels
  if(which.axis == "x") ax$heights = rev(ax$heights) else ax$widths = rev(ax$widths)
  
  ax$grobs = rev(ax$grobs)
  
  if(which.axis == "x") 
    
    ax$grobs[[2]]$y = ax$grobs[[2]]$y - unit(1, "npc") + unit(0.15, "cm") else
      
      ax$grobs[[1]]$x = ax$grobs[[1]]$x - unit(1, "npc") + unit(0.15, "cm")
  
  # Modify existing row to be tall enough for axis
  if(which.axis == "x") g$heights[[2]] = g$heights[g2$layout[ia,]$t]
  
  # Add new row or column for axis label
  if(which.axis == "x") {
    
    g = gtable_add_grob(g, ax, 2, 4, 2, 4) 
    
    g = gtable_add_rows(g, g2$heights[1], 1)
    
    g = gtable_add_grob(g, g2$grob[[6]], 2, 4, 2, 4)
    
  } else {
    
    g = gtable_add_cols(g, g2$widths[g2$layout[ia, ]$l], length(g$widths) - 1)
    
    g = gtable_add_grob(g, ax, pp$t, length(g$widths) - 1, pp$b) 
    
    g = gtable_add_grob(g, g2$grob[[7]], pp$t, length(g$widths), pp$b - 1)
    
  }
  
  # Draw it
  grid.draw(g)
  
}

It works pretty well. Thanks for writing this function!

hey thanks for this function but it does not seem to work very well. This is what I get running your code. As you can see there are some weird labels/texts on the upper right part of the chart. Any ideas what is causing this?

helpful for me. thanks a lot

@randomgambit wrote:

hey thanks for this function but it does not seem to work very well. This is what I get running your code. As you can see there are some weird labels/texts on the upper right part of the chart

I had the same problem, for dual y-axis if you remove line 59 from the ggplot_dual_axis.R it works fine.

Also, for dual x-axis example apparently there are points plotted outside of the plot area, but if you remove line 51 it seems to work fine.

Thanks for the code! Do you have any suggestion on how perfectly overlap the panels of the two plots?

Is it possible to add a label to the second x axis?

plot1.x = qplot(y = y1, x = x1, data = data.add.x)  + xlab('lab 1')
plot2.x = qplot(y = y1, x = x2, data = data.add.x) + xlab('lab 2')
ggplot_dual_axis(plot1.x, plot2.x, "x")

Does not work

Thanks a lot, @jslefche (and @ttnagata for corrections)! Very usefull!

I agree with @FrancescoRan, is there any option to perfect overlap both plots? Because my zeros in every axis are in different position...

It appears that changing line 59 to
g = gtable_add_grob(g, g2$grob[[13]], pp$t, length(g$widths), pp$b - 1)
fixes the right-y-axis title issue
I also added this on line 2 to flip the text:
plot2 <- plot2 + theme(axis.title.y = element_text(angle = 270))

Thanks to intelligentaccident. Your solution works perfectly.