r ggplot use plotmath expressions dynamically

Question

I want to change axis labels dynamically using ggplot. The code below is a simple version of what I'd like to do. It correctly displays a degree symbol in the y axis.The commented out ylab lines of code are what I'd like to do but fail. I want to create the plotmath code, assign it to a variable (e.g. yLabel) and then have ggplot interpret it.

library(data.table)
library(ggplot2)

DT <- data.table(timeStamp=c(1:12), ColN1=runif(12, 0, 10))
DT.long <- data.table::melt(
  DT, id.vars = c("timeStamp"))

yLabel <- "Temperature~(~degree~F)"
yLabel1 <- expression("Temperature~(~degree~F)")

p <- ggplot(data = DT.long, aes(x = timeStamp, y = value)) + 
  xlab("Time") + 
  #    ylab( expression(paste("Value is ", yLabel,","))) +
#  ylab(yLabel) +
#  ylab(yLabel1) +
  ylab(Temperature~(~degree~F)) +

    scale_y_continuous() +
  theme_bw() +
  geom_line()
print(p)

B Williams · Accepted Answer · 2017-12-11 00:58:15Z

3

Use bquote

Here is your dynamic component

temp <- 12

Assign it to the label using

ylab(bquote(Temperature ~is ~ .(temp) ~(degree~F)))

Or to address your additional question below

V = "Temperature is ("~degree~"F)"
W = "depth is ("~degree~"C)"

ggplot(data = DT.long, aes(x = timeStamp, y = value)) + 
  xlab("Time") +
  ylab(bquote(.(V)))

ggplot(data = DT.long, aes(x = timeStamp, y = value)) + 
  xlab("Time") +
  ylab(bquote(.(W)))

edited Dec 11, 2017 at 0:58

answered Dec 11, 2017 at 0:12

B Williams

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2 Comments

JerryN Over a year ago

This doesn't do the trick. I want to assign "Temperature is ..." to a variable (say V) and then use ylab(V). I tried ylab(bquote(.V). That didn't work.

Brian D Over a year ago

oddly, if you want to set V conditionally, like: V = case_when(degree>90 ~ bquote("hot^{AF}"), ...) this won't work with case_when(), you need to use if statements like if (degree>90) V = bquote("hot^{AF}")

Magnus · Accepted Answer · 2019-11-22 10:16:43Z

0

I had the same issue with dynamically modifying an axis label and B Williams answer helped me.

The solution:

dynamic <- "dynamic text"

# Put the dynamic text in its right context
str <- sprintf("Static label text [%s]", dynamic)

# Use multiplication "*" rather than "~" to build the expression to avoid unnecessary space 
complete_label <- bquote(.(str)[subscript]*"/L")

To verify that it works:

library(ggplot2)
ggplot() + labs(x = complete_label)

answered Nov 22, 2019 at 10:16

Magnus

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