ggplot2 中离散 x 轴的子组

Question

I would like to create a sub grouping in a ggplot2 (geom_point), meaning that I would like to shift discrete x values slightly according to a subgroup (see Figure).

I could achieve that by changing the discrete values to continuous and add a subgroup dependent shift value (see Fig.B), and than manually adjust the x labels. But I thought there is probably a more elegant way which deals with spacing and labeling issues.Below is a minimal example which hopefully describes what I mean.

library(ggplot2)
set.seed(1)
df <- data.frame(
    ID =       rep(seq(1,8),2),
    group =    rep(LETTERS[1:4],4),
    subgroup = c(rep("a",8),rep("b",8)),
    value = runif(16)
)
df$xpos <- as.numeric(df$group)+(as.numeric(df$subgroup)/4)


ggplot(data=df, aes(x=group, y= value, color=subgroup))+
  geom_point()+
    ggtitle("How it is")

ggplot(data=df, aes(x=xpos, y= value, color=subgroup))+
  geom_point() +
    ggtitle("How I would like it (without adjusted xAxes Labels)")

Answer 1

We can use position_dodge :

library(ggplot2)
ggplot(data=df, aes(x=group, y= value, color=subgroup))+
  geom_point(position=position_dodge(width=0.5))+
  ggtitle("How it is")

---

Data

set.seed(1)
df <- data.frame(
    ID =       rep(seq(1,8),2),
    group =    rep(LETTERS[1:4],4),
    subgroup = c(rep("a",8),rep("b",8)),
    value = runif(16)
)