ggplot2 legend items in a single horizontal row

Question

It seems that the code I wrote and tested last week has now suddenly decided to change the output even though nothing in the code or the version of R or Rstudio has changed.

Previously when I drew a plot with ggplot2 and asked for the legend to appear at the bottom of the plot, it automatically oriented the items into a single horizontal row. Now when I run the same code it places the item in a number of 2-row columns.

Here's an example:

mtcars$cyl <- (1:32)
subcars <- subset(mtcars, cyl<10)
subcars$cyl <- as.factor(subcars$cyl)

ggplot(subcars, aes(carb, mpg, group=cyl, colour=cyl)) + 
  geom_line() +
  theme_classic() +
  theme(plot.title = element_text(size = rel(2), face="bold", vjust=-4)) +
  theme(legend.position = "bottom") +
  theme(legend.direction = "horizontal") +
  labs(title="Title") 

As you can see, I have already tried adding in the line theme(legend.direction = "horizontal") but I still get a legend which displays the items in 5 2-row columns (yes, its not even just in two rows).

Now I can only assume that there has been some update that I was not aware of or something, so I'm willing to accept that I need to come up with a new strategy for dealing with this problem (which just wasn't a problem last week). Although I am a little bit confused about why my code has suddenly decided to stop working (any input on this welcome), I'm more interested in finding a fix for the immediate problem of my legend items being displayed in a strange configuration.

Answer 1

Add this to your plot:

+ guides(colour = guide_legend(nrow = 1))