Add colored arrow to axis of ggplot2 (partially outside plot region)

Question

I'd like to add a colored arrow (full length of the axis) to show time moving a in a direction (this can be assumed but for this plot there are no numeric values so I want the arrow to show the direction). I can use geom_segment to plot it but the part outside of the plot region is missing.

I've seen this post: R & ggplot2: How to get arrows under the axis label? but this solution is a hack of the axis title. This post: https://stackoverflow.com/a/10542622/1000343 shows lines outside text region but not a colored arrow.

MWE

library(ggplot2); library(grid); library(scales)

dat <- data.frame(Time=0:5, y=0:5)

ggplot(dat, aes(x=Time, y=y)) +
    geom_area(alpha=.1) + theme_bw() +
    scale_y_continuous(expand = c(0, 0)) +
    scale_x_continuous(expand = c(0, 0)) +
    theme(panel.grid.major = element_blank(), 
        panel.grid.minor = element_blank(),
          axis.text.x=element_blank(),
          axis.ticks.x=element_blank()
    )

I tried:

ggplot(dat, aes(x=Time, y=y)) +
    geom_area(alpha=.1) + theme_bw() +
    scale_y_continuous(expand = c(0, 0)) +
    scale_x_continuous(expand = c(0, 0)) +
    theme(panel.grid.major = element_blank(), 
        panel.grid.minor = element_blank(),
          axis.text.x=element_blank(),
          axis.ticks.x=element_blank()
    ) +
    geom_segment(aes(x=0, xend = 5 , y=0, yend = 0), size=1.5,
        arrow = arrow(length = unit(0.6,"cm")))

Giving

enter image description here

But I want

enter image description here

score 9 · Accepted Answer · edited May 23 '17 at 10:27

The problem appears just to be the clipping region (as answered here). Try:

p1<-ggplot(dat, aes(x=Time, y=y)) +
    geom_area(alpha=.1) + theme_bw() +
    scale_y_continuous(expand = c(0, 0)) +
    scale_x_continuous(expand = c(0, 0)) +
    theme(panel.grid.major = element_blank(), 
        panel.grid.minor = element_blank(),
          axis.text.x=element_blank(),
          axis.ticks.x=element_blank()
    ) +
    geom_segment(aes(x=0, xend = 5 , y=0, yend = 0), size=1.5,
        arrow = arrow(length = unit(0.6,"cm"))) 

gt <- ggplot_gtable(ggplot_build(p1))
gt$layout$clip[gt$layout$name=="panel"] <- "off"
grid.draw(gt)

to get

enter image description here

Nice approach. Thank you kindly. – Tyler Rinker Nov 26 '14 at 03:01 — Tyler Rinker, Nov 26 '14 at 03:01

score 9 · Answer 2 · answered Nov 26 '14 at 12:27

9

You could define your own axis grob,

library(ggplot2)

element_grob.element_custom <- function(element, ...)  {
  grid::segmentsGrob(0,1,1,1, arrow = arrow())
}
 ## silly wrapper to fool ggplot2
axis_custom <- function(...){
  structure(
    list(...), # this ... information is not used, btw
    class = c("element_custom","element_blank", "element") # inheritance test workaround
  ) 

}

ggplot(iris, aes(Sepal.Length, Sepal.Width)) +
  geom_line() +
  theme(axis.line = axis_custom(),
        axis.line.y=element_blank())

enter image description here

answered Nov 26 '14 at 12:27

baptiste

75,767
19
198
294

Thank you for this solution. Could you tell how to set color/width/fill for this arrow? – Yuriy Petrovskiy Mar 09 '15 at 12:01
I know it is late but here is the answer: https://stackoverflow.com/questions/22775567/change-line-colour-and-thickness-in-grid-curve-r . Simply add the gpar argument to the grid::segmentsGrob() function. Just remember to change gpar() in grid::gpar() in case you did not load grid – Jinglestar Oct 01 '18 at 02:23
to edit the arrowhead you simply add the arguments within the function arrow(): e.g., arrow(length=unit(0.1,'inches'), angle=40) – Jinglestar Oct 01 '18 at 02:34

score 3 · Answer 3 · answered Jan 13 '22 at 20:07

element_line(arrow = arrow(...)) has provided this functionality since September 2016. So all that's required is theme(axis.line.x = element_line(arrow = ...). For adjustment of the arrow see the documentation for element_line() and perhaps this superseding question.

library(dplyr)
library(ggplot2)

theme_set(theme_bw())

data = tibble(time = 0:5, y = 0:5)
ggplot(data, aes(x = time, y = y)) +
  geom_area(alpha = 0.1) +
  coord_cartesian(ylim = c(0, 5)) +
  labs(x = "time", y = "y") +
  scale_x_continuous(breaks = NULL, expand = c(0, 0)) +
  scale_y_continuous(expand = c(0, 0)) +
  theme(axis.line.x = element_line(arrow = arrow()),
        panel.grid.major.y = element_blank(),
        panel.grid.minor.y = element_blank())

score 2 · Answer 4 · edited Jan 14 '22 at 00:19

You can also add coord_cartesian(clip = "off"):

ggplot(dat, aes(x=Time, y=y)) +
  geom_area(alpha=.1) + theme_bw() +
  scale_y_continuous(expand = c(0, 0)) +
  scale_x_continuous(expand = c(0, 0)) +
  theme(panel.grid.major = element_blank(), 
        panel.grid.minor = element_blank(),
        axis.text.x=element_blank(),
        axis.ticks.x=element_blank()
  ) +
  geom_segment(aes(x=0, xend = 5 , y=0, yend = 0), size=1.5,
               arrow = arrow(length = unit(0.6,"cm"))) +
  coord_cartesian(clip = "off")

Add colored arrow to axis of ggplot2 (partially outside plot region)

4 Answers4

Linked

Related