How to have a factor outside the axis for an arrow in ggplot-CodePudding

I want to make an annotation with an arrow that goes outside a plot in ggplot. Using geom_curve changes the order of the factor, and I do not understand why.

Here is the example: let's consider the following plot:

df <- data.frame(ID = factor(c("A","B","C"),level = c("AA","B","C","A")),
           y = 1:3)

ggplot(df,aes(ID,y,color = ID)) 
  geom_point() 
  coord_flip(clip = "off") 
  scale_x_discrete(breaks = c("B","C","A"))

I want to keep the order of the vertical axis (B,C,A), and have an arrow pointing at the first point but from above the plot. I thus want to ass a factor before A that goes outside the plot:

ggplot(df,aes(ID,y,color = ID)) 
  geom_point() 
  geom_curve(data = data.frame(ID = factor("AA",level = c("AA","B","C","A")),
                               ID_end = "A",
                               y = 2,y_end = 1),
             aes(x = ID,xend = ID_end,
                 y = y ,yend = y_end),
             curvature = -.1,
             arrow =arrow(length = unit(2, "mm"),type = "closed"),
             color = "grey20" ,size = .2) 
  coord_flip(clip = "off") 
  scale_x_discrete(breaks = c("B","C","A"))

Here the vertical axis has the factors reordered, although I specified the same order in geom_curve. My arrow lies in the middle instead of being on the top/outside the plot.

How can I solve this problem?

CodePudding user response：

Does this help you? The arrow is not really "outside" the plot, but the order on the axis is maintained the way you want

df <- data.frame(
  ID = factor(c(1,2,3), labels=c("B","C","A")),
  y =c(2,3,1)
)

curvedata = data.frame(
  ID = 4, 
  ID_end = 3,
  y = 2,y_end = 1)

ggplot(df,aes(ID,y,color = ID)) 
  geom_point() 
  geom_curve(data=curvedata,
             aes(x = ID,xend = ID_end,
                 y = y ,yend = y_end),
             curvature = -.1,
             arrow =arrow(length = unit(2, "mm"),type = "closed"),
             color = "grey20" ,size = .2) 
  coord_flip(clip = "off")

CodePudding user response：

If you want to manually add a few things to a graph, use annotate(geom = "XXX") rather than geom_XXX with a custom data =.

Also, factor levels get converted to integers. It is easier to specify the integer value, rather than forcing the factor levels.

ggplot(df,aes(ID,y,color = ID)) 
    geom_point() 
    annotate(geom = "curve", x = -1L, xend = 1, y = 2, yend = 1,
             curvature = -.1,
             arrow =arrow(length = unit(2, "mm"),type = "closed"),
             color = "grey20" ,size = .2)  
    coord_flip(clip = "off") 
    scale_x_discrete(breaks = c("B","C","A"))