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How to add subscript to ggplot axis title when title starts with bracket symbol

April 22, 2023

I’ve looked on SO and haven’t found this exact issue or solution for this.
I am trying to label my x-axis: [NO3 + NO2] (mu mol L ^-1); where the 3 and 2 are subscripts, the mu shows as the symbol and the -1 is a superscript.

I think my main issue right now is that my x-axis title has to start with the "[" bracket.
I am using ggplot.

I am able to get the first part "[NO3" but haven’t been able to add anything past the subscripted 3:

xlab(bquote('[NO'* "" [3]))

Can’t seem to add anything after the 3 without getting errors

I’ve tried the following:

xlab(bquote('[NO'* "" [3] '+ NO' * "" [2] '] ('))

Error: unexpected string constant in:
"  #xlab(bquote([NO[3] + NO [2]]))
  xlab(bquote('[NO'* "" [3] '+ NO'"

and

xlab(bquote('[NO'* "" [3]~ '+ NO' * "" [2] '] ('))

Error: unexpected string constant in:
"  #xlab(bquote([NO[3] + NO [2]]))
  xlab(bquote('[NO'* "" [3]~ '+ NO' * "" [2] '] ('"

and

xlab(bquote('[NO'* "" [3]~ ~'+ NO' * "" [2] '] ('))

Error: unexpected string constant in:
"  #xlab(bquote([NO[3] + NO [2]]))
  xlab(bquote('[NO'* "" [3]~ ~'+ NO' * "" [2] '] ('"

and

xlab(bquote('[NO'* "" [3]'+ NO' * "" [2] '] ('))

Error: unexpected string constant in:
"  #xlab(bquote([NO[3] + NO [2]]))
  xlab(bquote('[NO'* "" [3]'+ NO'"

and

xlab(bquote('[NO'* "" [3]}~'+ NO' * "" [2] '] ('))

Error: unexpected '}' in:
"  #xlab(bquote([NO[3] + NO [2]]))
  xlab(bquote('[NO'* "" [3]}"

and

xlab(bquote('[NO'* "" [3]~'+ NO' * "" [2] '] ('))

Error: unexpected string constant in:
"  #xlab(bquote([NO[3] + NO [2]]))
  xlab(bquote('[NO'* "" [3]~'+ NO' * "" [2] '] ('"

and variations of…

labs(x = expression([NO[3]]))

Nothing seems to work…
Any suggestions?

Additionally, any way of splitting y-axis into three lines?
I was able to get what I want for y-axis title, which I have as:

ylab(bquote('\u03b1 '^{"chla"}~'\n(g C g chla'^{"-1"}~'hr'^{"-1"}~'/ ' *mu~ 'mol quanta' ~m^{"-2"}~'s'^{"-1"}~')'))

Is it possible to split this into 3 lines (the \n doesn’t seem to do anything here)?

Thank you.

>Solution :

We could do it this way:

Using atop we could stack the 3 parts of the y label.

With expression we specify the text of the label for x:

The first part of the label is [NO[3]]+NO[2] with a subscripted 3 and 2, the second part of the label is (mu mol L^-1) with the mu symbol and a superscripted -1:

library(ggplot2)

ggplot(mtcars, aes(x = mpg, y = wt)) +
  geom_point() +
  ylab(expression(atop('α' ^{"chla"} ~'', atop((g*C*g*chla^{"-1"}~hr^{"-1"}), '*mu~mol~quanta~m^{"-2"}~s^{"-1"}~'))))+
  xlab(expression(atop("[NO"[3]*"+"*NO[2]*"]"*(mu*"mol L"^-1))))