ggplot2 - annotate outside of plot

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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最佳答案

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

小开

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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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 = 14.25, # Set the position of the text to always be at '14.25'
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

小开

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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