best practices for 'object not found' scenarios when trying to use custom functions with `data.table` in R?
I'm attempting to set up I've searched everywhere and can't find a clear answer... I'm working with an 'object not found' behavior when I try to apply a custom function using `data.table`. I have a simple function that calculates the square of a number, and I want to use it within the `j` argument of a `data.table` statement. Here’s my setup: ```r library(data.table) data <- data.table(x = 1:5, y = 6:10) my_function <- function(num) { return(num^2) } data[, z := my_function(x)] ``` When I run this code, I receive the following behavior message: ``` behavior in my_function(x) : object 'x' not found ``` I tried defining `my_function` inside the `data.table` call: ```r data[, z := { my_function <- function(num) { return(num^2) }; my_function(x) }] ``` But this resulted in the same behavior. I suspect that the scenario relates to how `data.table` evaluates expressions within the `j` argument, especially with regard to the scope of variables. I also found that if I just use a standard operation like `x^2`, it works without any problems: ```r data[, z := x^2] ``` Can anyone guide to understand how to correctly use a custom function within `data.table`, or is there a better approach to achieve this? My development environment is Windows. This is part of a larger CLI tool I'm building.