Selecting factor for labels (ggplot2, directlabels)

2
votes

I'd like to use the package directlabels to label my plot. However, I'd like the label to be the ID of each point. Is there really no way to select which factor to label or did I miss that?

library(ggplot2)
library(directlabels)
df <- structure(
    list(id = 1:10,
         group = structure(c(1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L),
         .Label = c("A", "B"),
         class = "factor"),
         value1 = c(4, 1, 6, 2, 5, 7, 3, 2, 5, 8),
         value2 = c(6, 2, 6, 2, 8, 9, 7, 5, 2, 6)
         ),
.Names = c("id", "group", "value1", "value2"),
row.names = c(NA, -10L),
class = "data.frame")

p1 <- ggplot(df, aes(x=value1, y=value2)) + geom_point(aes(colour=group))
direct.label(p1)

enter image description here

2
rggplot2direct-labels
Why not just use geom_text? – Jaap
direct.label is used as an alternative of the legends (i.e. it is used to show the groups in your graph) not as a way to add labels on each point. For point labels use geom_text as Jaap mentions in his comment. – LyzandeR
@Jaap because my actual plot consists of around 200 points and with geom_text a lot of the labels are overlapped – erc

2 Answers

5
votes

Inspecting the code of direct.label.ggplot() shows that geom_dl() is called in the end. This function expects an aesthetic mapping and a positioning method. The positioning method used by default is the return value of default.picker("ggplot"), which uses call stack examination and in your case is equivalent to calling defaultpf.ggplot("point",,,). The following works for me:

p1 <- ggplot(df, aes(x=value1, y=value2)) +
  geom_point(aes(colour=group)) +
  geom_dl(aes(label = id), method = defaultpf.ggplot("point",,,))
p1

Plot

(Note that you don't need to call direct.label() anymore.)

The documentation of the directlabels package is indeed a bit scarce.

1
votes

You have to write a custom position method, like so:

label_all <- list( dl.trans(x = x + 0.5, y = y + 0.5), # shift every point up and right
                   gapply.fun(d) ) # include all points
direct.label(p1, method = label_all)

enter image description here

For another example, see the documentation, under "Specifying the positioning method as a list".