Removing an element from a lazy_dots list

[hong...@revolutionanalytics.com]

Is there an approved way of removing an element from an object of class lazy_dots?

require(lazyeval)

f <- function(a, ...)

lazy_dots(...)

lst <- f(1, x=2, y=3, z=4)

lst$z <- NULL

#Error in UseMethod("as.lazy") : 

#  no applicable method for 'as.lazy' applied to an object of class "NULL"

lst[["z"]] <- NULL

# this works

lst <- lst[-which(names(lst) == "z")]

# this also works

Setting the list element to NULL using the $ operator gives an error; but using [[ indexing works. I don't know if either behaviour will change in the future though. Using a negative index with which() also works, but that's rather clumsy.

I'm using lazyeval 0.1.10.

[Hadley Wickham]

I think lst[["z"]] <- NULL is probably best.
Hadley

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[hong...@revolutionanalytics.com]

Thanks Hadley. Can I assume that this won't change in the future?

Note that the error with lst$z can be fixed by defining a method for as.lazy.NULL:

as.lazy.NULL <- function(x, ...) NULL

This would give the same behaviour as using [[ indexing.

[Hadley Wickham]

That doesn't seem like consistent behaviour to me.
Hadley

[hong...@revolutionanalytics.com]

I'm not sure what you mean. It would be consistent with the behaviour of [[<-, which deletes the element. It would also be consistent with the common use of assigning a value of NULL to delete from a list. (I think the latter isn't great semantics honestly, but it's what we've got.)