How do one modify an expression?
On Tue, 3 Jul 2001, Uwe Ligges wrote:
Henrik Bengtsson wrote:
I am using expressions to annotate x and y labels in plots. I start of with a label as xlab <- expression(X) Note that it is the user that sets this. It could also be something more complicated as expression(sqrt(R*G)). Can I easily add a log[2] "around" this expression? I would like to get xlab <- expression(log[2](X)) I basically know nothing about expressions.
The following seems to work: plot(1:10, xlab= expression(log[2](X)))
He wants X <- expression(sqrt(R*G)) xlab <- ??? plot(1:10, xlab=xlab) to give the same result as plot(1:10, xlab=expression(log[2](sqrt(R*G)))) I believe. Try xlab <- substitute(log[2](foo), list(foo=X[[1]])) plot(1:10, xlab= xlab) If this is not exactly what is required, I am sure substitute is the right tool. Note: I would have used X <- quote(sqrt(R*G)) xlab <- substitute(log[2](foo), list(foo=X)) plot(1:10, xlab= xlab) and avoided the expression().
Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272860 (secr) Oxford OX1 3TG, UK Fax: +44 1865 272595 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._