How to reorder overlaying order of geoms but keep legend order intact in ggplot

Question

I know I can switch the line plotting order (i.e., which line is plotted 1st, 2nd, 3rd,...) by changing the levels of a grouping factor. However, doing so also switches the order of the ggplot legend.

How do I change the plotting order but retain the original legend order?

Example

Given the following data.frame:

dat <- data.frame(id = rep(factor(letters[1:3]),3), y = c(1:3,3,2,1,1,3,1), x = rep(1:3,each = 3))

I can switch the line plotting order by changing the levels of the id factor:

e.g., by reordering the levels using dat$id = relevel(dat$id, 'c').

Using the following ggplot code for the original and relevel'ed data:

library(ggplot2)

#Create coloring objects to kep color consistent:
  cols <- rep(1:3,3)
    names(cols) <- letters[1:3]

#Create line graph:
  ggplot(dat,aes(x=x,y=y,color=id)) + geom_line(size = 2) + 
    scale_colour_manual('id',values=cols)  ##set custom static coloring

produces the following 2 graphs:

^{Left: original level order for factor id | Right: using relevel}

Notice that the lines have been successfully reordered: line c goes from being printed last (and therefore on top) to being printed first (and therefore on the bottom).

However, the legend has also switched order!

How do I retain the legend order from the left graph but modify the line printing order to match that of the right graph?

a dirty move could be to plot two geom_lines : geom_line(size = 2, show.legend = FALSE) + geom_line(aes(color=relevel(id, 'c')), size=2) — user20650
Yup, I know how to do it that way :p. Thanks! However, given the amount and complexity of my actual data, that approach is less than ideal. I'm hoping for some sort of hidden argument I'm not aware of or some other more direct approach than the one you've suggested. — theforestecologist
Use the breaks argument in scale_colour_manual: ggplot(dat, aes(x = x, y = y, color = relevel(id, "c"))) + geom_line(size = 2) + scale_colour_manual('id', values = cols, breaks = levels(dat$id)) — Henrik

tjebo tjebo · Accepted Answer · 2018-09-06T22:10:03

You will probably have found a solution by now. Just saw this question is still 'unanswered' and here a suggestion, based on @Hendrik's comment - which was very helpful but not the entire solution (his code gives your plot 2)

dat$id2 = relevel(dat$id, 'c') # just create a dummy column with the releveled factors

ggplot(dat) + 
  geom_line(aes(x = x, y = y, color = id2), size = 2) + 
# use your dummy column for the line order
  scale_colour_manual('id',values = cols, breaks = levels(dat$id))  
# use @Hendriks break suggestion

How to reorder overlaying order of geoms but keep legend order intact in ggplot

1 Answers