Writing Functions With a “data” Argument

Question

I want to write a function that can take columns within a data frame or column names and the data frame they come from as arguments.

df <- data.frame(x = c(1:         


        

Answer 1

The problem is that when calling my_fxn(x, y, z, df) the object x is not defined. Hence df$x does not return column x but NA.

Consider this small example:

df <- data.frame(x = 1:3, y = 4:6)
x <- "y"
df$x # returns column x
[1] 1 2 3
df[,x] #returns column y since the value which is stored in x is "y"
[1] 4 5 6

To circumvent your problem you can use data[, aaa] instead of data$aaa. Yet another alternative would be to use the dplyr package where you can use select(data, aaa).