Addressing x and y in aes by variable number

Question

I need to draw a scatterplot with addressing variables by their column numbers instead of names, i.e. instead of ggplot(dat, aes(x=Var1, y=Var2)) I need something like ggplot(dat, aes(x=dat[,1], y=dat[,2])). (I say 'something' because the latter doesn't work).

Here is my code:

showplot1<-function(indata, inx, iny){   dat<-indata   print(nrow(dat)); # this is just to show that object 'dat' is defined   p <- ggplot(dat, aes(x=dat[,inx], y=dat[,iny]))   p + geom_point(size=4, alpha = 0.5) }  testdata<-data.frame(v1=rnorm(100), v2=rnorm(100), v3=rnorm(100), v4=rnorm(100), v5=rnorm(100)) showplot1(indata=testdata, inx=2, iny=3) 

# Error in eval(expr, envir, enclos) : object 'dat' not found 

Answer 1

Your problem is that aes doesn't know your function's environment and it only looks within global environment. So, the variable dat declared within the function is not visible to ggplot2's aes function unless you pass it explicitly as:

showplot1<-function(indata, inx, iny) {     dat <- indata     p <- ggplot(dat, aes(x=dat[,inx], y=dat[,iny]), environment = environment())     p <- p + geom_point(size=4, alpha = 0.5)     print(p) } 

Note the argument environment = environment() inside the ggplot() command. It should work now.