ggplot: align plots together and add common labels and legend

I have a data.frame in which one variable has many levels (e.g. param1, param2and param3). All these levels have the same unit (concentration mg L-1) but they have different ranges of values.

For example

param1 ranges from 0 to 0.4

param2 ranges from 0 to 0.07

param3 ranges from 0 to 3000

Instead of using my data.frame, I used diamonds to create a reproducible example

library(dplyr)
library(ggplot2)
df <- diamonds %>%
  dplyr::filter(cut%in%c("Fair","Ideal")) %>%
  dplyr::filter(clarity%in%c("I1" ,  "SI2" , "SI1" , "VS2" , "VS1",  "VVS2")) %>%
  dplyr::mutate(new_price = ifelse(cut == "Fair", 
                                   price/100000, 
                                   price/10))

As Fair and Ideal have different ranges of values, I created two separate plots for Fair and Ideal to be able to assign the breaks in y axis

I want the two axes in the two plots to have the same number of decimals. I used fmt_decimals() from here.

library(dplyr)
library(ggplot2)
library(gridExtra)
library(grid)
#function to assign decimals for axes
fmt_dcimals <- function(decimals=0){
  function(x) format(x,nsmall = decimals,scientific = FALSE)
}


f1 <- 
 ggplot(df[df$cut == "Fair",], aes(x=carat , y= new_price, color = color))+
  geom_point(alpha = 0.3)+
  scale_y_continuous( limits = c(0,0.20), breaks=c(0, 0.05,0.1,0.15,0.2), labels = fmt_dcimals(2))+
  scale_x_continuous( limits = c(0,5.2), breaks=c(0,1,2,3,4,5), labels = fmt_dcimals(2))+
  facet_wrap(~cut) +
  labs(x = "",
       y = "")


f2 <- 
  ggplot(df[df$cut == "Ideal",], aes(x=carat , y= new_price, color = color))+
  geom_point(alpha = 0.3)+
  scale_y_continuous( limits = c(0,2000), breaks=c(0, 250,500,750,1000, 1250, 1500, 1750, 2000), labels = fmt_dcimals(2))+
  scale_x_continuous( limits = c(0,5.2), breaks=c(0,1,2,3,4,5), labels = fmt_dcimals(2))+
  facet_wrap(~cut) +
  labs(x = "",
       y = "")


f <- gridExtra::arrangeGrob(f1,f2, ncol=1, 
                            bottom=grid::textGrob(label= expression(Flow~(m^{3}~s^{-1})),
                                                  gp= gpar(fontsize=12, fontface="bold", col="black")),
                            left=grid::textGrob(label=expression(Concentration~mg~L^{-1}), rot=90, 
                                                gp= gpar(fontsize=12, fontface="bold", col="black")))

grid::grid.newpage() 
grid::grid.draw(f)

RESULT

The top and bottom plots are not aligned along x axis.

I can fix this using ggarrange() from egg package

library(egg)
f_1 <- ggarrange( f1, f2)
f_1

Now the two plots are perfectly aligned.

QUESTIONS

Any suggestions to align the two plots along x axis using gridExtra? If not Can I add common labels for axes using egg?

and how can I add only one legend for the two plots?

UPDATE

Thanks to @eipi10

I updated it as below

library(cowplot)
# Function to extract legend
# https://github.com/hadley/ggplot2/wiki/Share-a-legend-between-two-ggplot2-graphs
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) }

# Extract legend as a grob
leg = g_legend(f1)

# Remove legend from plots
f1 = f1 + theme(legend.position = "none")
f2 = f2 + theme(legend.position = "none")

# Lay out the two
f_1 = plot_grid(f1, f2, ncol =1, align="v")

f_3 <- grid.arrange(
  arrangeGrob(f_1,  
              bottom=grid::textGrob(label= expression(Flow~(m^{3}~s^{-1})),
                                    gp= gpar(fontsize=12, fontface="bold", col="black")),
              left=grid::textGrob(label=expression(Concentration~mg~L^{-1}), rot=90, 
                                  gp= gpar(fontsize=12, fontface="bold", col="black"))),
  leg, 
  widths=c(9,1))

But it seems using cowplot, there is no vertical y line on the right side of the plot?

Asked By: shiny

Source

Answer #1:

I think you can everything you want using only ggplot2, including a shared x-axis, shared axis titels and proper spacing. To me that seems easier than messing around with gtables.

This is a perfectly fine attempt:

ggplot(df[df$cut %in% c("Fair", "Ideal"),], aes(x=carat , y= new_price, color = color))+
  geom_point(alpha = 0.3)+
  scale_y_continuous(labels = fmt_dcimals(2))+
  scale_x_continuous(limits = c(0,5.2), breaks=c(0,1,2,3,4,5), labels = fmt_dcimals(2))+
  facet_wrap(~cut, scales = 'free_y', nrow = 2) +
  labs(x = "",
       y = "")

If you really want to have custom breaks, you can use a break function to supply those:

make_breaks <- function(ranges) {
  if(ranges[2] > 1) {
    c(0, 250,500,750,1000, 1250, 1500, 1750, 2000)
  } else {
    c(0, 0.05,0.1,0.15,0.2)
  }
}

ggplot(df[df$cut %in% c("Fair", "Ideal"),], aes(x=carat , y= new_price, color = color))+
  geom_point(alpha = 0.3)+
  scale_y_continuous(labels = fmt_dcimals(2), breaks = make_breaks)+
  scale_x_continuous(limits = c(0,5.2), breaks=c(0,1,2,3,4,5), labels = fmt_dcimals(2))+
  facet_wrap(~cut, scales = 'free_y', nrow = 2) +
  labs(x = "",
       y = "")

Answered By: shiny

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