Adding greek character to axis title - r

Question

I want to add a greek character to the y-axis of my barplot in R.
The problem is that I need this character to be integrated in the title. I want to write:
Diameter of aperture ("mu"m)
in the axis label.
With
ylab=expression()
I can write the greek character, with
ylab="axis title"
I can write the title with proper spaces between the words.
But I can't find a way to put all these together and write a proper label with a greek word in the axis label. I hope I was clear enough.

Answer 1

If you're using plotmath{grDevices}, the main help page (plotmath) contains an example of what you appear to want:
xlab = expression(paste("Phase Angle ", phi))
or for your case, I guess:
ylab = expression(paste("Diameter of aperture ( ", mu, " )"))
Does this work for you?

Answer 2

I think I followed your question properly. The ~ forces a space between characters in a call to expression(). Is this what you want?
plot(1:3, ylab = expression("Diameter of apeture (" * mu ~ "m)"),
, xlab = expression("Force spaces with ~" ~ mu ~ pi * sigma ~ pi)
, main = expression("This is another Greek character with space" ~ sigma))

Answer 3

And if you want to substitute variables in the text, use bquote. For instance, if you have a variable mu and want to show it in the title, then use the following idiom:
mu <- 2.8
plot(1:3, main=bquote(mu == .(mu)))
The part enclosed in .() will be substituted, so that the value of mu will be printed and not the greek "mu" character. Consult the R help on bquote for details.

Answer 4

This should be much more straight forward with latex2exp:
require(latex2exp)
plot(1, xlab = TeX('$\\mu$'))

Answer 5

And, in case you were dealing with an estimated quantity, plotmath{grDevices} also offers the possibility of adding a hat to your greek letter:
ylab = expression(paste("Diameter of aperture ( ", hat(mu), " )"))
The mu enclosed in hat() does the trick.

Answer 6

I give an updated answer to Chase's plot example (from 2011) above while working with Windows 10 with a suitable TrueType Font with the help package utf8 on R 3.62.
In my answer, I assign a value to μ. The unicode characters I just call out by their hex (??) code. The space is just a 'space' inside quotes. See my answer here:
See also:
http://www.unicode.org/Public/10.0.0/ucd/UnicodeData.txt
utf8-package {utf8}
# pi small case
utf8_print("\u03C0")
"π"
# sigma small case
utf8_print("\u03C3")
"σ"
μ <- abs(digamma(1))
μseq <- seq(μ,3*μ,μ)
dev.new()
plot(μseq, ylab = "Diameter of apeture ( μ m)",
, xlab = "Force spaces with ~ μ \u03C0 \u03C3 \u03C0 ",
, main = "This is another Greek character with space \u03C3")
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