Set categorical axis labels with scales "free" ggplot2

Question

I am trying to set the labels on a categorical axis within a faceted plot using the ggplot2 package (1.0.1) in R (3.1.1) with scales="free". If I plot without manually setting the axis tick labels they appear correctly (first plot), but when I try to set the labels (second plot) only the first n labels are used on both facets (not in sequence as with the original labels).

Here is a reproducible code snippet exemplifying the problem:

foo <- data.frame(yVal=factor(letters[1:8]), xVal=factor(rep(1:4,2)), fillVal=rnorm(8), facetVar=rep(1:2,each=4))
## axis labels are correct
p <- ggplot(foo) + geom_tile(aes(x=xVal, y=yVal, fill=fillVal)) + facet_grid(facetVar ~ ., scales='free')
print(p)
## axis labels are not set correctly
p <- p + scale_y_discrete(labels=c('a','a','b','b','c','d','d','d'))
print(p)

I note that I cannot set the labels correctly within the data.frame as they are not unique. Also I am aware that I can accomplish this with arrange.grid, but this requires "manually" aligning the plots if there are different length labels etc. Additionally, I would like to have the facet labels included in the plot which is not an available option with the arrange.grid solution. Also I haven't tried viewports yet. Maybe that is the solution, but I was hoping for more of the faceted look to this plot and that seems to be more similar to grid.arrange.

It seems to me as though this is a bug, but I am open to an explanation as to how this might be a "feature". I also hope that there might be a simple solution to this problem that I have not thought of yet!

Answer 1

The easiest method would be to create another column in your data set with the right conversion. This would also be easier to audit and manipulate. If you insist on changing manually:

You cannot simply set the labels directly, as it recycles (I think) the label vector for each facet. Instead, you need to set up a conversion using corresponding breaks and labels:

p <- p + scale_y_discrete(labels = c('1','2','3','4','5','6','7','8'), breaks=c('a','b','c','d','e','f','g','h'))
print(p)

Any y axis value of a will now be replaced with 1, b with 2 and so on. You can play around with the label values to see what I mean. Just make sure that every factor value you have is also represented in the breaks argument.

Answer 2

I think I may actually have a solution to this. My problem was that my labels were not correct because as someone above has said - it seems like the label vector is recycled through. This line of code gave me incorrect labels.

ggplot(dat, aes(x, y))+geom_col()+facet_grid(d ~ t, switch = "y", scales = "free_x")+ylab(NULL)+ylim(0,10)+geom_text(aes(label = x))

However when the geom_text was moved prior to the facet_grid, the below code gave me correct labels.

ggplot(dat, aes(x, y))+geom_col()+geom_text(aes(label = x))+facet_grid(d ~ t, switch = "y", scales = "free_x")+ylab(NULL)+ylim(0,10)

There's a good chance I may have misunderstood the problem above, but I certainly solved my problem so hopefully this is helpful to someone!