R help - Oct 2010 - Displaying a variable as an expression into a plot label, but the variable has brackets

I'm attempting to insert variables as expressions into labels for my plots,
but I'm running into the issue that characters in my labels aren't
allowed
in expressions, notably '[' and ']'. An input string of
"[^3H]5-CT" needs to
be displayed as [3H]5-CT with the 3 as superscript. But brackets aren't
particularly liked in expressions. I know I can do something like

mtext(expression(paste("[",phantom()^3,"H]5-CT (0.8
nM)")),3,2)

but "[^3H]5-CT" is saved as a single variable. I'm not really sure
what to
do other than splitting the string into sections that can and can't be
evaluated as expressions and then pasting as necessary.

Thanks,
Jared

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On Oct 12, 2010, at 12:53 PM, Jared Blashka wrote:
> I'm attempting to insert variables as expressions into labels for my  
> plots,
> but I'm running into the issue that characters in my labels aren't
> allowed
> in expressions, notably '[' and ']'. An input string of
"[^3H]5-CT"
> needs to
> be displayed as [3H]5-CT with the 3 as superscript. But brackets  
> aren't
> particularly liked in expressions. I know I can do something like
>
> mtext(expression(paste("[",phantom()^3,"H]5-CT (0.8
nM)")),3,2)
>
> but "[^3H]5-CT" is saved as a single variable. I'm not really
sure
> what to
> do other than splitting the string into sections that can and can't be
> evaluated as expressions and then pasting as necessary.
bquote to the rescue!

 > varname <- "[^3H]5-CT"
 > plot(1,1,xlab=expression(varname))  # nope
 > plot(1,1,xlab=bquote(.(varname)) )  # Yes
 > plot(1,1,xlab=bquote(.(varname)*"(0.8 nM)") )
        # Yes, note need for "*" or "~" as plotmath
separator.


=
David Winsemius, MD
West Hartford, CT