[R] variable of mathematics string not interpreted

[Duncan Murdoch]

delpacho wrote:
> Hi everybody,
>
> my goal is to display symbols on the x-axis of a barplot.
> I read some mathematics strings in a file and convert them to an expression
> as follows:
>
> tt<- scan(file = fstr ,'what' ='character', sep = "");
>
> for (iaa in 1:length(tt)) { 
> tt[iaa]<-do.call(expression, lapply(tt[iaa], as.name));
> }
>
> I obtained the following result:
>
> tt =
>
> expression(`alpha[tr]`, beta, widthD, `S[ts]^-5("[165,275]Hz")`, 
>     `S[ts]^2("[165,275]Hz")`, `S[ts]^-5("[275,460]Hz")`,
> `S[r]^2("[165,275]Hz")`, 
>     `S[r]^-5("[275,460]Hz")`, `S[r]^3("[100,165]Hz")`,
> `T[ts]^4("[165,275]Hz")`, 
>     `T[ts]^7("[21,30]Hz")`, `T[ts]^8("[13,21]Hz")`, `T[r]^7("[21,30]Hz")`, 
>     `T[r]^8("[13,21]Hz")`, `T[r]^9("[8,13]Hz")`, `E("[100,165]Hz")`, 
>     `E("[165,275]Hz")`, `E("[60,100]Hz")`, `E("[8,13]Hz")`,
> `E("[30,60]Hz")`, 
>     `E("[21,30]Hz")`)
>
> only the strings without "`" are interpreted properly when I put the
> property names.arg =tt in barplot (ex:beta displays the greek letter,
> whereas `alpha[tr]` displays alpha[tr]), could you explain me why these
> symbol "`" intervenes when I convert the strings to an expression and/or how 
> can I have the symbols associated with the strings displayed properly?
>   

You used as.name() to convert the strings to expressions, so it 
converted them to names.  You really want to parse them, not just 
convert them to names.  For example,

 > tt <- c("alpha[tr]", "beta", "S[ts]^-5(\"[165,275]Hz\")")
 > barplot(1:3, names.arg=parse(text=tt))

Duncan Murdoch