Optional segment end

[teunbrand]

This PR aims to fix #5140, fix #3627 and fix #3617.

Briefly, it makes one of xend/yend optional in geom_segment(). The missing aesthetic gets filled by x and y respectively.

Visual demo:

devtools::load_all("~/packages/ggplot2/")
#> ℹ Loading ggplot2

df <- data.frame(x = c("a", "b", "c"), y = c(2.3, 1.9, 3.2))

ggplot(df) + geom_segment(aes(x, y, yend = 0))

ggplot(df) + geom_segment(aes(x, y, xend = 0))

set.seed(42)
df <- data.frame(
  x = rep(letters[1:3], each = 2),
  y = rpois(6, 10),
  group = rep(LETTERS[1:2], 3)
)

p <- ggplot(df, aes(x, y, colour = group))

# Want the ends stay stable? Define them.
p + geom_segment(
  aes(xend = x, yend = 0),
  position = position_dodge(width = 0.9)
)

# Want the ends to be dodged too? Omit one
p + geom_segment(aes(yend = 0), position = position_dodge(width = 0.8))

^{Created on 2023-01-21 with reprex v2.0.2}

[thomasp85]

Am I right in understanding that this does not fully fix the dodging issue - it only help for fully vertical or fully horizontal segments?

[teunbrand]

Indeed, it only helps with horizontal or vertical segments. I'm not sure what dodging with other angles should do, but that isn't addressed by this PR.

[thomasp85]

intuitively dodging a segment would use the width/height of it's bounding box

[thomasp85]

LGTM - as discussed we will tackle dodging fully in another PR (or multiple)

[teunbrand]

Thanks for the review Thomas! I'm merging this despite a failing test on devel (explained here: #5296 (comment))

[smouksassi]

Hi I had a question regarding the automatic flipping running in current ggplot2 we get the below
do we still need to manually specify yend = 0 or xend = 0 for the new approach to work ?
or will the code automatically flip / know what we mean by x/y ends ?
(sorry unable to try the dev version at the moment)

library(patchwork)
library(ggplot2)
#> Warning: package 'ggplot2' was built under R version 4.2.3
set.seed(42)
df <- data.frame(
  x = rep(letters[1:3], each = 2),
  y = rpois(6, 10),
  group = rep(LETTERS[1:2], 3)
)

a<- ggplot(df ,aes(x=x,y=y, colour = group))+
  geom_point(size=5,alpha=0.5,
             position = position_dodge(width = 0.9))+
  geom_segment(aes(yend=0,xend=x),
               position = position_dodge(width = 0.9))
b<- ggplot(df ,aes(x=y,y=x, colour = group))+
  geom_point(size=5,alpha=0.5,
             position = position_dodge(width = 0.9))+
  geom_segment(aes(xend=0,yend=x),
               position = position_dodge(width = 0.9))

a | b

^{Created on 2023-05-10 with reprex v2.0.2}

[teunbrand]

Yes you'd still need to specify yend = 0 or xend = 0, it doesn't do anything that is not in the data.
The new thing is that you can leave out the yend = x or xend = x. Within one layer, you can leave out either xend or yend to have it filled with x and y respectively. The segment geom doesn't really have an orientation, so flipping aesthetics should just work. This filling in happens after positions adjustments, so the missing aesthetic just 'follows' the main one.

devtools::load_all("~/packages/ggplot2/")
#> ℹ Loading ggplot2
library(patchwork)

set.seed(42)
df <- data.frame(
  x = rep(letters[1:3], each = 2),
  y = rpois(6, 10),
  group = rep(LETTERS[1:2], 3)
)

a<- ggplot(df ,aes(x=x,y=y, colour = group))+
  geom_point(size=5,alpha=0.5,
             position = position_dodge(width = 0.9))+
  geom_segment(aes(yend=0), # Note, 'xend' is missing
               position = position_dodge(width = 0.9))
b<- ggplot(df ,aes(x=y,y=x, colour = group))+
  geom_point(size=5,alpha=0.5,
             position = position_dodge(width = 0.9))+
  geom_segment(aes(xend=0), # Note, 'yend' is missing
               position = position_dodge(width = 0.9))

a | b

^{Created on 2023-05-10 with reprex v2.0.2}

[smouksassi]

thank you I will figure out how to switch
from geom_segment(aes(yend=0)) to geom_segment(aes(xend=0) depending on user input.
letting the user do lollipop plots has never been easier! thank you

[joranE]

Was this broken at some point? The examples at the top no longer work in 3.4.4 (haven't tried 3.5.0 yet), geom_segment complains about missing required aesthetics.

[teunbrand]

I don't think it was ever broken, but these examples should only work from 3.5.0 onwards

[joranE]

Gotcha, sorry for the noise. The date it was merged made me think it was incorporated earlier, sorry!