facet_wrap Title wrapping & Decimal places on free_y axis (ggplot2)

Question

I have a set of code that produces multiple plots using facet_wrap:

ggplot(summ,aes(x=depth,y=expr,colour=bank,group=bank)) +
geom_errorbar(aes(ymin=expr-se,ymax=expr+se),lwd=0.4,width=0.3,position=pd) +
geom_line(aes(group=bank,linetype=bank),position=pd) +
geom_point(aes(group=bank,pch=bank),position=pd,size=2.5) +
scale_colour_manual(values=c("coral","cyan3", "blue")) +
facet_wrap(~gene,scales="free_y") +  
theme_bw()

With the reference datasets, this code produces figures like this:

I am trying to accomplish two goals here:

1. Keep the auto scaling of the y axis, but make sure only 1 decimal place is displayed across all the plots. I have tried creating a new column of the rounded expr values, but it causes the error bars to not line up properly.
2. I would like to wrap the titles. I have tried changing the font size as in Change plot title sizes in a facet_wrap multiplot, but some of the gene names are too long and will end up being too small to read if I cram them on a single line. Is there a way to wrap the text, using code within the facet_wrap statement?

Answer 1

Probably cannot serve as definite answer, but here are some pointers regarding your questions:

1. Formatting the y-axis scale labels.

First, let's try the direct solution using format function. Here we format all y-axis scale labels to have 1 decimal value, after rounding it with round.

formatter <- function(...){
  function(x) format(round(x, 1), ...)
}

mtcars2 <- mtcars
sp <- ggplot(mtcars2, aes(x = mpg, y = qsec)) + geom_point() + facet_wrap(~cyl, scales = "free_y")
sp <- sp + scale_y_continuous(labels = formatter(nsmall = 1))

The issue is, sometimes this approach is not practical. Take the leftmost plot from your figure, for example. Using the same formatting, all y-axis scale labels would be rounded up to -0.3, which is not preferable.

The other solution is to modify the breaks for each plot into a set of rounded values. But again, taking the leftmost plot of your figure as an example, it'll end up with just one label point, -0.3

Yet another solution is to format the labels into scientific form. For simplicity, you can modify the formatter function as follow:

formatter <- function(...){
  function(x) format(x, ..., scientific = T, digit = 2)
}

Now you can have a uniform format for all of plots' y-axis. My suggestion, though, is to set the label with 2 decimal places after rounding.

---

2. Wrap facet titles

This can be done using labeller argument in facet_wrap.

# Modify cyl into factors
mtcars2$cyl <- c("Four Cylinder", "Six Cylinder", "Eight Cylinder")[match(mtcars2$cyl, c(4,6,8))]

# Redraw the graph
sp <- ggplot(mtcars2, aes(x = mpg, y = qsec)) + geom_point() +
  facet_wrap(~cyl, scales = "free_y", labeller = labeller(cyl = label_wrap_gen(width = 10)))
sp <- sp + scale_y_continuous(labels = formatter(nsmall = 2))

It must be noted that the wrap function detects space to separate labels into lines. So, in your case, you might need to modify your variables.

Answer 2

This only solved the first part of the question. You can create a function to format your axis and use scale_y_continous to adjust it.

df <- data.frame(x=rnorm(11), y1=seq(2, 3, 0.1) + 10, y2=rnorm(11))

library(ggplot2)
library(reshape2)

df <- melt(df, 'x')

# Before
ggplot(df, aes(x=x, y=value)) + geom_point() +
  facet_wrap(~ variable, scale="free")

# label function
f <- function(x){
  format(round(x, 1), nsmall=1)
}

# After
ggplot(df, aes(x=x, y=value)) + geom_point() +
  facet_wrap(~ variable, scale="free") +
  scale_y_continuous(labels=f)

Answer 3

scale_*_continuous(..., labels = function(x) sprintf("%0.0f", x)) worked in my case.