Looping over variables in ggplot

Question

I want to use ggplot to loop over several columns to create multiple plots, but using the placeholder in the for loop changes the behavior of ggplot.

If I have this:

t <- data.frame(w = c(1, 2, 3, 4), x = c(23,45,23, 34), 
y = c(23,34,54, 23), z = c(23,12,54, 32))

This works fine:

ggplot(data=t, aes(w, x)) + geom_line()

But this does not:

i <- 'x'
ggplot(data=t, aes(w, i)) + geom_line()

Which is a problem if I want to eventually loop over x, y and z. Any help?

Answer 1

You just need to use aes_string instead of aes, like this:

ggplot(data=t, aes_string(x = "w", y = i)) + geom_line() 

Note that w then needs to be specified as a string, too.