Add group levels to data frame

Question

In How to change the order of facet labels in ggplot (custom facet wrap labels) it is described how to add group levels for later use in a sorted facet grid.

How can I generate group levels to mtcars that will turn the number of cylinders in the reversed order?

What is wrong with the answer provided in the question to which you linked? — mnel, Nov 29 '12 at 01:29
`Group = gl(5, 20, labels = LETTERS[1:5])` assumes that I have 5*20 items, but how will I have to sort it with 30+50+20 items for example? — Jonas Stein, Nov 29 '12 at 01:31
something like `within(mtcars, Group = factor(cylinder, levels = rev(sort(unique(cylinder))))` should suffice. — mnel, Nov 29 '12 at 01:33
works on mtcars and with my data too. Could you make it an answer? Thx. — Jonas Stein, Nov 29 '12 at 01:52

mnel · Accepted Answer · 2012-11-29T02:01:00.940

2

The trick here is to sort the unique values, and then set the levels as the reverse.

for example.

mtcars <- within(mtcars, Group <- factor(cyl, levels = rev(sort(unique(cyl)))))


ggplot(mtcars) + geom_point() + facet_grid(~Group)

edited Nov 29 '12 at 02:01

answered Nov 29 '12 at 01:54

mnel

that works. Now I can combine it with the results from the cited question. – Jonas Stein Nov 29 '12 at 02:10

1 Answers1