[R] legend with math (greek letters) symbols

[David Winsemius]

On Sep 13, 2014, at 5:55 PM, Julio Sergio Santana wrote:

> I need to add a legend with three entries that should
> contain a greek letter (lambda). I learnt that it is
> possible using the function expression. So I need to
> build the expressions from the lambdas vector, and I
> simply cannot do it. This is the uggly result I got:
>
>
>  x <- 0:20
>  cc <- c("yellow", "springgreen", "navyblue")
>  lambdas <- c(6, 10, 13)
>  ds <- as.data.frame(lapply(lambdas, function(ll) dpois(x, ll)))
>  names(ds) <- lambdas
>  funcs <- list(plot, lines)
>
>  for (i in 1:3) {
>      ff <- funcs[[1+(i!=1)]]
>      ff(x,ds[[i]], type="o", pch=21,bg=cc[i])
>  }
>
>  # I can't build the expressions:
>  q <- list(expression(lambda==6), expression(lambda==10),
>            expression(lambda==13))
>
>  legend("topright",
>         legend=q,
>         lty=1, pch=21, pt.bg=cc)

q <- expression(lambda==6, lambda==10 ,lambda==13)
  legend("topright",
          legend=q,
          lty=1, pch=21, pt.bg=cc)

-- 
David.

>
> legend() doesn't interpret the expressions and then it doesn't show
> the lambda symbol.
>
> Do you have any comments on this?
>
> Thanks,
>
> -Sergio.
>
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David Winsemius, MD
Alameda, CA, USA