[R] how to make plotmath expression work together with paste

[Uwe Ligges]

Paul Johnson wrote:

> Recent questions about using plotmath have renewed my interest in this question
> 
> I want to have expressions take values of variables from the
> environment. I am able to use expressions, and I am able to use paste
> to put text and values of variables into
> plots.  But the two things just won't work together.


See my article "R Help Desk: Automation of Mathematical Annotation in 
Plots" in  R News 2(3), 32-34.

Uwe Ligges



> Here is some example code that shows what I mean.
> 
> 
> plot(NA,xlim=c(0,100),ylim=c(0,100))
> 
> #show plot math works
> text(16, 22, expression(slope == frac(partialdiff * f(hat(theta)),
>      partialdiff * hat(theta))))
> 
> # I want to put values of variables into the middle of expressions
>  avar1 <- 10
> 
> # prove I am able to use paste!
> text(40,40, paste("a word",avar1,"other words")
> 
> # But I'm completely frustrated by the problem of making paste and
> # expression work together.
> 
> amath1 <- expression(slope == frac(partialdiff * f(hat(theta)), 
> partialdiff * hat(theta)))
> 
> # still works
> text(10,60,amath1)
> 
> 
> # paste breaks math output
> text(60,60, paste (amath1, "=" , avar1) )
> 
> 
> # Can't paste expression
> text(20,30, paste("a word",avar1, expression( partialdiff )))
> 
> 
> 
> # paste does not work anymore--value of avar1 not replaced
> text(50,80, expression(paste("slope" == frac(partialdiff *
> f(hat(theta)),partialdiff * hat(theta)), avar1)))
> 
> n<-12
> 
> # This does get the avar1 value in the string and put it in, but it
> # piles the labels on top of each other. Wish they went side by side
>  text(12, 15, labels=c(expression(bar(x) == sum(frac(x[i], n), i==1,
> )), paste("gamma =",avar1)),cex = .8)
> 
> 
> 
> 
> --
> Paul E. Johnson
> Professor, Political Science
> 1541 Lilac Lane, Room 504
> University of Kansas
> 
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