On Fri, Jun 8, 2018 at 2:09 PM, Berry, Charles <ccbe...@ucsd.edu> wrote:
>
>
>> On Jun 8, 2018, at 1:49 PM, Hadley Wickham <h.wick...@gmail.com> wrote:
>>
>> Hmmm, yes, there must be some special case in the C code to avoid
>> recycling a length-1 logical vector:
>
>
> Here is a version that (I think) handles Herve's issue of arrays having one
> or more 0 dimensions.
>
> subset_ROW <-
> function(x,i)
> {
> dims <- dim(x)
> index_list <- which(dims[-1] != 0L) + 3
> mc <- quote(x[i])
> nd <- max(1L, length(dims))
> mc[ index_list ] <- list(TRUE)
> mc[[ nd + 3L ]] <- FALSE
> names( mc )[ nd+3L ] <- "drop"
> eval(mc)
> }
>
> Curiously enough the timing is *much* better for this implementation than for
> the first version I sent.
>
> Constructing a version of `mc' that looks like `x[i,,,,drop=FALSE]' can be
> done with `alist(a=)' in place of `list(TRUE)' in the earlier version but
> seems to slow things down noticeably. It requires almost twice (!!) as much
> time as the version above.
I think that's probably because alist() is a slow way to generate a
missing symbol:
bench::mark(
alist(x = ),
list(x = quote(expr = )),
check = FALSE
)[1:5]
#> # A tibble: 2 x 5
#> expression min mean median max
#> <chr> <bch:tm> <bch:tm> <bch:tm> <bch:tm>
#> 1 alist(x = ) 2.8µs 3.54µs 3.29µs 34.9µs
#> 2 list(x = quote(expr = )) 169ns 219.38ns 181ns 24.2µs
(note the units)
Hadley
--
http://hadley.nz
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