[R] problem with `legend' + `substitute'

[Uwe Ligges]

Timur Elzhov wrote:
> 
> Hello, R experts!
> 
> I'd like to add the somewhat complicated expression as "legend"
> to the plot:
> 
>   x  <-  1
>   T  <- 10
> 
>   plot(x)
>   legend   ( 1.0 ,1.0
>             ,substitute ( paste ( Sr["2"] ,GaMnO["5.541"]
>                                  ,", T = " ,T ,"K"
>                                 )
>                          ,list (T = T)
>                         )
>             ,bg = "white"
>             ,xjust = 0.5
>             ,yjust = 0.5
>            )
> 
> So, I get plot with not one, but *six* instances of the desired expression,
> one under another!


The structure of your S expression is the point:

  temp <- substitute(paste(Sr["2"], GaMnO["5.541"], 
            ", T = ", T, "K"), list (T = T))
  length(temp)   # ah! 6!
  str(temp)      # that's it! Try also:
  temp[[1]]
  temp[[2]]      # ...



> Ok, trying to use `text' ..
> 
>   plot(x)
>   text     ( 1.0 ,1.0
>             ,substitute ( paste ( Sr["2"] ,GaMnO["5.541"]
>                                  ,", T = " ,T ,"K"
>                                 )
>                          ,list (T = T)
>                         )
>             ,adj = c(0.5, 0.5)
>            )
> 
> Well, `text' works properly!  but why `legend' behaves so?

Because it plots one line per element of your S expression, which
consists of 6!


> (I'm running R v1.6.1 on Debian woody system for i386)


What you can do is:

 x  <-  1
 Te  <- 10
 # substitute at first:
 temp <- substitute(paste(Sr["2"] * GaMnO["5.541"], ",", 
     T == Te * K), list(Te = Te))
 plot(x)
 # and construct a single expression (length = 1) by using do.call():
 legend(1, 1, do.call("expression", list(temp)), 
     bg = "white", xjust = 0.5, yjust = 0.5)

Uwe Ligges
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