如何使用ggplot2在R中添加大小可变的y轴标签，而又不更改绘图宽度？

Question

I have a plot I made with ggplot2 in R that I would like to add a horizontal text label to the y-axis. However, depending on the length of my text, R compresses my plot accordingly to create a fixed width image. However, I need the plots to be identical length and have identical starting and stopping positions (margins) no matter the text width.

I tried changing the plot margins by overwriting the default ggplot2 theme elements like so:

library(ggplot2)
png(filename="sample.png", width=5600, height=70)
plot.data <- data.frame(start.points=c(my_start),end.points=c(my_stop))
p <- ggplot(plot.data)
p + geom_rect(aes(xmin=start.points, xmax=end.points, ymin=0, ymax=1), fill="red") + theme_bw() + ylab("sample_title") + 
theme(axis.title.y = element_text(size = 30, colour = "black", angle = 0), axis.text = element_blank(), legend.key = element_blank(), axis.ticks = element_blank(), plot.margin = unit(c(0.1, 0.1, 0.1, 12), "lines"))
dev.off()

So this makes a nice plot, but depending on my axis label the entire plot is stretched or compressed. Can someone please help me find a way to hold the plot width and margins static while changing the axis label text? If the axis label text is too long and it extends outside of the left-hand image border on into the plot itself, that is ok, as long as the plot doesn't change.

Thanks for any help! I've been banging my head on this for way too long.

Answer 1

Changing the margins doesn't help in this case because they just add fixed space in addition to your axis label. You could pad your axis label to your expected maximum length to keep the dimensions the same, it's not the most elegant solution but I don't think element_text can do a fixed width at the moment (maybe someone can correct me on this). Anyways, you could try one of these:

ylab(sprintf("%40s", "sample_title"))

(padding the axis title to 40 characters with spaces - although total width will still vary depending on your font)

ylab(paste(sprintf("%40s", ""), "\nsample_title\n")

(adding a line of 40 spaces above your axis title and an empty line below - should always give you the same width as long as the axis title isn't longer than that)