Strict pluck

[hadley]

In base R, [[ sometimes returns an error and sometimes returns NULL:

row[[col]]	Zero-length	OOB (int)	OOB (chr)	Missing
NULL	NULL	NULL	NULL	NULL
Atomic	Error	Error	Error	Error
List	Error	Error	NULL	NULL

pluck() eliminates this inconsistently by (effectively) always return NULL. We need a strict equivalent that eliminates the inconsistency in the opposite direction: by always throwing an error.

[hadley]

We could call it chuck() or suck()

[daniel-barnett]

Were you thinking something like the following (but without the strict parameter)? If so, I can clean it up and make a PR.

test.list <- list(a = 1:5, b = letters[1:5], c = list(abc = 123))
test.atom <- 1:10

> # strict_pluck()
> pluck(NULL, integer(0), strict = TRUE)
Error: `.x` must not be NULL.
> pluck(NULL, 100, strict = TRUE)
Error: `.x` must not be NULL.
> pluck(NULL, "adsaf", strict = TRUE)
Error: `.x` must not be NULL.
> pluck(NULL, NA_integer_, strict = TRUE)
Error: `.x` must not be NULL.

> pluck(test.list, integer(0), strict = TRUE)
Error: Can't find index.
> pluck(test.list, 100, strict = TRUE)
Error: Can't find index.
> pluck(test.list, "adsaf", strict = TRUE)
Error: Can't find index.
> pluck(test.list, NA_integer_, strict = TRUE)
Error: Can't find index.

> pluck(test.atom, integer(0), strict = TRUE)
Error: Can't find index.
> pluck(test.atom, 100, strict = TRUE)
Error: Can't find index.
> pluck(test.atom, "adsaf", strict = TRUE)
Error: Can't find index.
> pluck(test.atom, NA_integer_, strict = TRUE)
Error: Can't find index.

[hadley]

Exactly!

[hadley]

A PR would be great 😄

[daniel-barnett]

So, I also have this working for environments and S4 objects. For environments, it errors if the object doesn't exist in the environment, and for S4 if the object doesn't have the desired slot. This would the desired behaviour, right?

The other big one is indexing by function, but (correct me if I'm wrong) I don't think we can really make this strict as it relies on whatever that function's behaviour is.

[hadley]

That all sounds correct to me