Displaying 1 result from an estimated 1 matches for "droplowmpg".
2014 Feb 11
1
getting environment from "top" promise
...nvironment in which
to evaluate the expression.
Consider:
setClass("A", representation(df = "data.frame"))
setMethod("subset", "A", function(x, subset) {
env <- parent.frame(2)
x@df <- x@df[eval(substitute(subset), x@df, env),,drop=FALSE]
x
})
dropLowMpg <- function(x, cutoff=20) {
invisible(subset(x, mpg > cutoff))
}
a <- new("A", df=mtcars)
dropLowMpg(a)
The above works just fine, because we figured out that we need to evaluate
in the grand-parent frame to avoid the frame of the generic call. But now
let's assume A has...