[R] graph label greek symbol failure

[Gavin Simpson]

On Wed, 2009-08-19 at 14:20 +0100, e-letter wrote:
> On 18/08/2009, Gavin Simpson <gavin.simpson at ucl.ac.uk> wrote:
> > On Tue, 2009-08-18 at 13:06 +0100, e-letter wrote:
> >> On 17/08/2009, Michael Knudsen <micknudsen at gmail.com> wrote:
> >> > On Mon, Aug 17, 2009 at 12:51 PM, e-letter <inpost at gmail.com> wrote:
> >> >
> >> >> I have tried to add the delta (δ) symbol to the y axis label and the
> >> >> result is &D, using the command:
> >> >>
> >> >> ...ylab="δt"...
> >> >
> >> > Try ylab = expression(delta*t) instead.
> >> >
> >> This does not work, the result is
> >> expression(delta*t)
> >
> > It works for the rest of us who suggested this.
> >
> > plot(1:10, ylab = expression(delta*t))
> >
> True, but the following commands fails:
> plot(1:10,ylab="temperature expression(delta*t)")
> plot(1:10,ylab="temperature" expression(delta*t))
> Error: syntax error, unexpected SYMBOL, expecting ',' in
> "plot(1:10,ylab="temperature" expression"
> 
> So I want to be able to have 'δt' and 'temperature δt' as a y-axis label.

Ah, but you never said that. We aren't mind readers you know ;-)

What you need is an expression that will, when used, give you a text
label containing "Temperature δt". What you have done is create a
character string of the literal "...expression(delta*t)" which is of
course why it is printed as the label - after all , you asked R to do
this.

I suggest you read the plotmath help page, accessed via:

?plotmath

executed at the prompt.

I found this expression stuff complicated when I first started out,
until I realised that whatever gets passed to expression(....) has to be
a syntactically valid R command. So for your particular example we need:

plot(1:10, ylab = expression(Temperature ~ delta*t))

Temperature is treated as the character string "Temperature"; the "~"
means leave some space between the bits either side of "~"; delta is a
special name that will get replaced by the relevant glyph; the "*"
juxtaposes delta and "t", ie places them next to one another without any
space in between.

I see that Baptiste has also just replied with a similar solution to
mine. Baptiste's solution quotes "temperature " with the spacing being
stated explicitly. Whilst both yield similar results, using "~" and not
having to quote things results in a simpler solution, IMHO.

HTH

Gavin

> 
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