How to get the column's name in apply function?

Question

I am trying to make a function that makes a small report for every column in a data frame by using apply. In the report I want to use the name of the column so I have to 'extract' it somehow and that is what my question is about. How do I get the name of the column in my apply function?

Here is a simple example where I want to use the name of the column in the graph title: (for now I just hardcoded the name as 'x')

x <- c(1,1,2,2,2,3)
y <- c(2,3,4,5,4,4)
Tb <- data.frame(x,y)
Dq_Hist <- function(Tab){
  Name <- 'x'
  Ttl <- paste('Variable: ',Name,'')
  hist(Tab, main=Ttl, col=c('grey'), xlab=Name)
}
D <- apply(Tb, MARGIN=2, FUN=Dq_Hist)

Answer 1

I found out that you can call sapply with an index list and use this index in the function. So the solution is:

   x <- c(1,1,2,2,2,3)
   y <- c(2,3,4,5,4,4)
   Tb <- data.frame(x,y)
   Dq_Hist <- function(i){
     Name <- colnames(Tb)[i]
     Ttl <- paste('Variable: ',Name,'')
     hist(Tb[,i],main=Ttl,col=c('grey'),xlab=Name)
   }
   D <- sapply(1:ncol(Tb),Dq_Hist)