Question

I am a newcomer to R. Last week I had a long and complicated function working perfectly. The program was letting me pick a subset of columns and doing various manipulations on that subset. The function must work ‘function(arg1=first_header_name, arg2=second_header_name,….)’. I have cleared the console, removed the old history file. I have read the manual again, I have checked the .csv file to make sure everything there is still the same. I have gone back and reworked it all step by step and I have the place where this new problem occurs. As it is a very long function, I am only going to reproduce it in a simplified version of the part that is suddenly not working.

 elbow <- function(arg1,arg2) {
   my_data <- read.csv("data.csv", header=TRUE, sep=",") 
   average_A <- (arg1 + arg2)
   average_A
 }
 elbow(A3,A5)
 # Error in elbow(A3, A5) : object 'A3' not found

Column headers are A3,A4,A5,A7,A8,A9,B2,B3,B5,B6,B7,B9

What stupid little error am I making? This is driving me batty. It has to be something trivial.

Answer 1

Here’s my guess at what might work the way you wanted:

elbow <- function(arg1,arg2) {
   my_data <- read.csv("data.csv", header=TRUE, sep=",") 
   average_A <- my_data[[arg1]] + my_data[[arg2]]   # "[[" evaluates args
   average_A
 }
 elbow('A3','A5')  # entered a character literals

You should realize that the rest of my_data will have evaporated and be garbage collected after return from the elbow call. I could have showed you how to use your original expression following attach(), which would have been arguably safe within that function, but that would have violated my religious principles.