Adding index to points in ggplot

Question

I have a basic plot, with a small number of points on. I would like to label the points with a numeric index, and then have the full description of the point in the legend. These is commonly seen on maps, as shown in the following example:

However, there seems to be no built-in function within ggplot to add an index. Here is a MWE of the basic concept:

df <- data.frame(x = 6:10, y = 6:10, id = 1:5)
df$label <- paste0("Label", df$id)

library(ggplot)

# Basic plot
ggplot(df, aes(x, y)) +
  geom_point() +
  geom_label(aes(label = id), nudge_x = 0.2)

What I have tried so far is to map the index label to the point by an aesthetic. This way, it creates a legend as follows:

ggplot(df, aes(x, y)) +
  geom_point(aes(fill = label)) +
  geom_label(aes(label = id), nudge_x = 0.2)

This is getting close to a proper index, but ideally, the legend shape would show the numeric count instead of the same shapes. Here is a manual edit of the potential end result:

Does anyone have an idea on how to do this in an elegant way?

There is a previous, unanswered question which is similar to this one: Add numbers to ggplot legend

Having searched further, I realise this question is a duplicate. As always, I was just using the wrong search term: https://stackoverflow.com/questions/24801987/numbered-point-labels-plus-a-legend-in-a-scatterplot?rq=1 — Michael Harper, Feb 19 '18 at 15:59
Although I still feel there should be a better way of doing this, as having an index is quite a common thing to do when making maps! — Michael Harper, Feb 19 '18 at 16:00

score 0 · Accepted Answer · answered Feb 19 '18 at 15:56

My best workaround to this problem:

Create a new column within the original dataset which joins the ID and the Label
Use the new column as the aesthetic for the legend
Hide the legend key

This is the code:

df$legend <- paste0(df$id,": ",df$label)

ggplot(df, aes(x, y)) +
  geom_point(aes(fill = legend), alpha = 0) +
  geom_point() +
  geom_label(aes(label = id), nudge_x = 0.2) +
  scale_fill_discrete(name = "Index") +
  theme(legend.key = element_blank(),
        legend.key.width = unit(0, "cm"),
        legend.title.align=0.5)

Still feels a bit messy though so interested to hear other ways of doing this.

Adding index to points in ggplot

1 Answers1