How to write a function that calls a function that calls data.table?

Question

The package data.table has some special syntax that requires one to use expressions as the i and j arguments.

This has some im

Answer 1

I think you might be tieing yourself up in knots. This works:

library(data.table)
foo <- function(data, by){
  by <- by
  data[, .N, by=by]
}

DT <- data.table(mtcars)
foo(DT, 'gear')

plotfoo <- function(data, by){
  foo(data, by)
}
plotfoo(DT, 'gear')

And that method supports passing in character values:

> gg <- 'gear'
> plotfoo <- function(data, by){
+   foo(data, by)
+ }
> plotfoo(DT, gg)
   gear  N
1:    4 12
2:    3 15
3:    5  5