95

I would like to associate sample size values with points on a plot. I can use geom_text to position the numbers near the points, but this is messy. It would be much cleaner to line them up along the outside edge of the plot.

For instance, I have:

df=data.frame(y=c("cat1","cat2","cat3"),x=c(12,10,14),n=c(5,15,20))

ggplot(df,aes(x=x,y=y,label=n))+geom_point()+geom_text(size=8,hjust=-0.5)

Which produces this plot: enter image description here

I would prefer something more like this: enter image description here

I know I can create a second plot and use grid.arrange (a la this post) but it would be tedious to determine the spacing of the textGrobs to line up with the y-axis. Is there an easier way to do this? Thanks!

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  • 1
    This could be done with secondary axis which I think it's under development. But if you want to give it a try follow this link groups.google.com/forum/?fromgroups=#!topic/ggplot2/_3Pm-JEoCqE Commented Sep 13, 2012 at 15:56
  • Hmm interesting...I was wondering if Hadley was going to implement this. However, I'm getting some weird errors trying to load devtools: call: if (!version_match) { error: argument is of length zero. Commented Sep 14, 2012 at 0:01
  • All I can say is that devtools works for me. You should try posting a question if you cannot solve it. Commented Sep 14, 2012 at 0:04
  • I worked around it by installing ggplot2 0.9.2.1 from the .zip on CRAN. Now the code provided in the link by @LucianoSelzer doesn't run (multiple arguments to the guide_axis). Maybe too much for tonight? I'll sleep on it and see if I can't figure it out in the morning Commented Sep 14, 2012 at 0:16
  • see also stackoverflow.com/a/17493256/471093 Commented Jun 17, 2016 at 22:58

6 Answers 6

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98

This is now straightforward with ggplot2 3.0.0, since now clipping can be disabled in plots by using the clip = 'off' argument in coordinate functions such as coord_cartesian(clip = 'off') or coord_fixed(clip = 'off'). Here's an example below.

    # Generate data
    df <- data.frame(y=c("cat1","cat2","cat3"),
                     x=c(12,10,14),
                     n=c(5,15,20))
    
    # Create the plot
    ggplot(df,aes(x=x,y=y,label=n)) +
      geom_point()+
      geom_text(x = I(1), # Set text's position to the right end of the plot
                hjust = 0,
                size = 8) +
      coord_cartesian(xlim = c(10, 14), # This focuses the x-axis on the range of interest
                      clip = 'off') +   # This keeps the labels from disappearing
      theme(plot.margin = unit(c(1,3,1,1), "lines")) # This widens the right margin

enter image description here

Thanks to @captain-hat for the suggestion to use I(1) in geom_text(x = I(1) to set the text position to the far right end of the plot.

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5 Comments

How can you do this for x-axis of a box-plot?
This is definitely the easiest option, thanks! @ktyagi maybe you sorted this by now, but you would use exactly the same argument but specifying ylim instead or xlim
It's worth noting that this does not appear to work with coord_polar
Does anyone know how the code should be if the x-axis have dates? I was trying with as.Date("2020-09-01") but get the message "Error in as.Date() : 'origin' must be supplied"
As of ggplot 3.5.0 you can set x = I(1) within annotate() in order to place labels on the right-most side of the plot
70

You don't need to be drawing a second plot. You can use annotation_custom to position grobs anywhere inside or outside the plotting area. The positioning of the grobs is in terms of the data coordinates. Assuming that "5", "10", "15" align with "cat1", "cat2", "cat3", the vertical positioning of the textGrobs is taken care of - the y-coordinates of your three textGrobs are given by the y-coordinates of the three data points. By default, ggplot2 clips grobs to the plotting area but the clipping can be overridden. The relevant margin needs to be widened to make room for the grob. The following (using ggplot2 0.9.2) gives a plot similar to your second plot:

library (ggplot2)
library(grid)

df=data.frame(y=c("cat1","cat2","cat3"),x=c(12,10,14),n=c(5,15,20))

p <- ggplot(df, aes(x,y)) + geom_point() +            # Base plot
     theme(plot.margin = unit(c(1,3,1,1), "lines"))   # Make room for the grob

for (i in 1:length(df$n))  {
p <- p + annotation_custom(
      grob = textGrob(label = df$n[i], hjust = 0, gp = gpar(cex = 1.5)),
      ymin = df$y[i],      # Vertical position of the textGrob
      ymax = df$y[i],
      xmin = 14.3,         # Note: The grobs are positioned outside the plot area
      xmax = 14.3)
 }    

# Code to override clipping
gt <- ggplot_gtable(ggplot_build(p))
gt$layout$clip[gt$layout$name == "panel"] <- "off"
grid.draw(gt)

enter image description here

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8 Comments

isn't it easier to have one geom_text layer at x=Inf, hjust>=1, and turn off clipping?
@jslefche, you should note that the solution offered by @baptiste is much simpler. p = p + geom_text(aes(label = n, x = Inf, y = y), hjust = -1). Then turn off the clipping. Although the alignment can be off slightly.
and how does one turn off clipping?
@ThomasBrowne To turn off clipping, see the last three lines of code above.
Unfortunately the x position at which you need to position the text change with the range of the x axis. So you need to use a value of x that is relative to the axis range. Here's my solution. I get the x ggplot computed axis range with xlim.range <- ggplot_build(plot)$panel$ranges[[1]]$x.range. Then I use this as x position: x = xlim.range[1] - diff(xlim.range)/10 and it works!
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7

Simplier solution based on grid

require(grid)

df = data.frame(y = c("cat1", "cat2", "cat3"), x = c(12, 10, 14), n = c(5, 15, 20))

p <- ggplot(df, aes(x, y)) + geom_point() + # Base plot
theme(plot.margin = unit(c(1, 3, 1, 1), "lines"))

p

grid.text("20", x = unit(0.91, "npc"), y = unit(0.80, "npc"))
grid.text("15", x = unit(0.91, "npc"), y = unit(0.56, "npc"))
grid.text("5", x = unit(0.91, "npc"), y = unit(0.31, "npc"))
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2 Comments

Much simpler, at first glance but ... font doesn't match ggplot2 defaults so you then have to fiddle with those settings, and harder to position the text due to using npc units. Probably ends up just as complex.
Exactly: for a quick-and-dirty fix where you just need to slap on some labels and don’t plan to tweak the plot further, this method is perfect. However, in practice, even small changes to axis limits, etc., can misalign the labels. That’s why the more integrated solution — like the one by Sandy Muspratt above — which scales with changes, is usually preferable.
3

Another option could be using annotate from ggplot2 which is almost the same as using geom_text:

library(ggplot2)
df=data.frame(y=c("cat1","cat2","cat3"),x=c(12,10,14),n=c(5,15,20))
ggplot(df,aes(x=x,y=y)) + 
  geom_point() + 
  annotate("text", x = max(df$x) + 0.5, y = df$y, label = df$n, size = 8) +
  coord_cartesian(xlim = c(min(df$x), max(df$x)), clip = "off") +
  theme(plot.margin = unit(c(1,3,1,1), "lines"))

Created on 2022-08-14 by the reprex package (v2.0.1)

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1

This particular example might be a case for ggh4x::guide_axis_manual

# remotes::install_github("teunbrand/ggh4x")
library(ggplot2)

df <- data.frame(y=c("cat1","cat2","cat3"), x=c(12,10,14), n=c(5,15,20))

ggplot(df, aes(x=x, y=y)) +
  geom_point() +
  guides(y.sec=ggh4x::guide_axis_manual(title = element_blank(), breaks = df$y, labels = paste0("n=",df$n)))

Created on 2023-08-24 with reprex v2.0.2

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1

Another option which is similar in spirit to the approach by @jan-glx but using just vanilla ggplot2 would be to use the so-called secondary axis trick which means to use a secondary or duplicated axis to add the annotations.

However, in the case of a discrete scale this is slightly more involved as a discrete scale does not allow for a secondary axis. Hence, we have to switch to a continuous scale first by converting the discrete y axis variable to a numeric using e.g. as.numeric(factor(...)).

library(ggplot2)

df$y_num <- as.numeric(factor(df$y))

ggplot(df, aes(x = x, y = y_num, label = n)) +
  geom_point() +
  scale_y_continuous(
    # Fix the breaks
    breaks = unique(df$y_num),
    labels = df$y,
    # Set default discrete scale amount of expansion
    expand = c(0, .6),
    sec.axis = dup_axis(
      breaks = unique(df$y_num),
      labels = paste0("n = ", df$n)
    )
  ) +
  theme(
    # Multiply by `.pt` to convert to `geom_text` font size
    # (the latter is measured in "mm", while the axis text uses "pt")
    axis.text.y.right = element_text(size = 8 * .pt),
    axis.ticks.y.right = element_blank(),
    axis.title.y.right = element_blank()
  )

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