Sang Sang - 2 months ago 17
R Question

multiple bquote items in legend of an R plot

Following works, (copy & paste into R)

a=123
plot(1,1)
legend('bottomleft',legend=bquote(theta == .(a)))


I want to have multiple items in the legend.
All with greek letters.
As a simple example, if I repeat the item twice the code does not work anymore

a=123
plot(1,1)
legend('bottomleft',legend=c(bquote(theta == .(a)),bquote(theta == .(a))))


I have tried many more complicated expressions but they all did not work.

Any help will be appreciated.

Answer

In this case, plotmath is not able to coerce the list of calls to expressions.

> cs <- c(bquote(theta == .(a)),bquote(theta == .(a)))
> cs
[[1]]
theta == 123

[[2]]
theta == 123

> sapply(cs, class)
[1] "call" "call"

You can make this work if you coerce to expressions yourself:

> c(as.expression(bquote(theta == .(a))), as.expression(bquote(theta == .(a))))
expression(theta == 123, theta == 123)
> plot(1,1)
> legend('bottomleft',legend= c(as.expression(bquote(theta == .(a))), 
+                               as.expression(bquote(theta == .(a)))))

Another way is to coerce the original list of calls to expressions using sapply:

plot(1,1)
legend("bottomleft", 
       sapply(c(bquote(theta == .(a)), bquote(theta == .(a))), as.expression))