R help - Apr 2004 - legend(1,1,expression(a<-"10^-6"))

hi all,

I have a problem with showing properly formated mathematical expressions 
in a plot.

The following works:

plot(1:10)
legend(1,10, expression(10^-6))

Howver, if my expression is kept in a char variable, I don't know how to 
show it in the legend.

# I have
st_"10^-6"
# I try to do this
plot(1:10)
legend(1,10, expression(st))
# which doesn't turn out as expected


Is it possible to convert a string into expression? Or is there a 
different way of doing what I want to do?

Thanks in advance for your help.
viet

Viet Nguyen wrote:
> hi all,
> 
> I have a problem with showing properly formated mathematical expressions 
> in a plot.
> 
> The following works:
> 
> plot(1:10)
> legend(1,10, expression(10^-6))
> 
> Howver, if my expression is kept in a char variable, I don't know how
to
> show it in the legend.
> 
> # I have
> st_"10^-6"
You have got a completely outdated version of R, if the code given above 
really works. Note that _ has long been depeceated and does no longer 
work for assignments.

> # I try to do this
> plot(1:10)
> legend(1,10, expression(st))
> # which doesn't turn out as expected
> 
?parse: "parse returns the parsed but unevaluated expressions in a list. 
Each element of the list is of mode expression."

  st <- "10^{-6}"
  plot(1:10)
  legend(1,10, parse(text = st))

Uwe Ligges


> Is it possible to convert a string into expression? Or is there a 
> different way of doing what I want to do?
> 
> Thanks in advance for your help.
> viet
> 
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