preserve = "single" has no effect for continuous axes

[karawoo]

#2774 made me realize that the preserve = "single" argument to position_dodge() and position_dodge2() has no effect when the x axis is continuous:

library("ggplot2")

df <- data.frame(
  x = c(4, 5, 6, 4, 6),
  y = c("A", "A", "A", "B", "B")
)

ggplot(df, aes(x = x)) +
  geom_bar(position = position_dodge2(preserve = "single")) +
  facet_wrap(~ y)

Compare to the version with a discrete x axis:

ggplot(df, aes(x = factor(x))) +
  geom_bar(position = position_dodge2(preserve = "single")) +
  facet_wrap(~ y)

Created on 2018-07-27 by the reprex package (v0.2.0).

Like @clauswilke said on the other issue, I'm not sure what the expectation should be for continuous axes, but maybe we should at least document that preserve only works for discrete axes.

[tungttnguyen]

Saw this on SO. Not sure if this is related. If not please move it wherever appropriate.

geom_text not properly positioned when using position_dodge(preserve=“single”) in bar plot
https://stackoverflow.com/q/51813898/786542

v1 <- LETTERS[1:2]
v2 <- letters[1:2]
v3 <- c("x","y")
g <- expand.grid(v1,v2,v3)
val=c(sample(10,8))
df<- data.frame(g,val)
df<- df[-8,]


    df %>% ggplot() +
      geom_bar(aes(x=Var2, y=val, fill=Var3, group=Var3), 
               stat="identity", 
               position=position_dodge(preserve="single"))+
      geom_text(aes(x=Var2, y=val+1, label=val, group=Var3), 
                position=position_dodge(width=1))+
  facet_grid(Var1~Var2, scale="free_x")

Using position_dodge2 alignes the bar with the labelling (however, the bar is the then centered and not aligned with the bars in the other facets).

df %>% ggplot() +
  geom_bar(aes(x=Var2, y=val, fill=Var3, group=Var3), stat="identity", 
           position=position_dodge2(preserve="single"))+
  geom_text(aes(x=Var2, y=val+1, label=val, group=Var3), 
            position=position_dodge2(width=1))+
  facet_grid(Var1~Var2, scale="free_x")

[teunbrand]

I think this has been fixed somewhere along the way, so I'm gonna mark this as completed.

library(ggplot2)

df <- data.frame(
  x = c(4, 5, 6, 4, 6),
  y = c("A", "A", "A", "B", "B")
)

ggplot(df, aes(x = x)) +
  geom_bar(position = position_dodge2(preserve = "single")) +
  facet_wrap(~ y)

^{Created on 2023-06-25 with reprex v2.0.2}