How to pass a string argument to expression function in ggplot2?

Question

I'm writing a wrapper function around ggplot2 and having difficulty with one of the string arguments passed. Here's the sample code

myPlot <- function(tim, labx){
  ggplot(subset(dat,TIME=tim), aes(x=WT, y=Var))+
    geom_point(size=2)+
    facet_wrap(~Dose)+
    scale_x-continuous(expression(bold("Predicted"~labx~"Concentration ("*mu*"g/mL)")))
}

When I say myplot(100, "Week3"), my x-axis label is showing as "Predicted labx Concentration (µg/mL)" instead of "Predicted Week3 Concentration (µg/mL)". How do I fix this?

Welcome to Stack Overflow! Could you make your problem reproducible by sharing a sample of your data so others can help (please do not use str(), head() or screenshot)? You can use the reprex and datapasta packages to assist you with that. See also Help me Help you & How to make a great R reproducible example? — Tung
– Tung, Commented Oct 24, 2018 at 16:08

bdemarest · Accepted Answer · 2018-10-24 18:04:51Z

1

One solution is to use bquote() instead of expression(), and use .() inside of bquote to evaluate character (string) variables.

Below is a fully reproducible example of the issue.

library(ggplot2)

labx = "Week3"

p = ggplot(data.frame(x=1:5, y=1:5), aes(x, y)) + 
    geom_point() + 
    xlab(bquote(bold(Predicted~.(labx)~Concentration~(mu*g/mL))))
p

edited Oct 24, 2018 at 18:04

answered Oct 24, 2018 at 17:29

bdemarest

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1 Comment

Jafar Shaik Over a year ago

Perfect. Worked like a charm !!!. Thanks so much. I was struggling for so long to solve this.

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