From ccberry @ending from uc@d@edu  Fri Jun  8 23:49:51 2018
From: ccberry @ending from uc@d@edu (Berry, Charles)
Date: Fri, 8 Jun 2018 21:49:51 +0000
Subject: [Rd] Subsetting the "ROW"s of an object
In-Reply-To: <CABdHhvGJm5CCObSQ+4VqP10TMM5b220GzWyZZJD+66xOOYPrtQ@mail.gmail.com>
References: <CABdHhvF9R3Mpk9pMMy8wa=qXzGta9cXdb9BYKT4P69QRuU3rig@mail.gmail.com>
 <F528270A-70D5-457B-BE73-4562540CFA16@ucsd.edu>
 <CABdHhvFcNObMmNvs9BfDk6sgZspNFK2++a571RrwLz-2taF4oQ@mail.gmail.com>
 <83c9327a-d8f1-66da-c75f-13e67a0140e0@fredhutch.org>
 <C43ED250-AD89-4ECC-97B8-038231DB475D@ucsd.edu>
 <CABdHhvHDFyEBESAFaE99rm5_xgdG08ooCAFFkshCvY86y9RmCg@mail.gmail.com>
 <A15318D9-58CD-4514-AD9D-4B9F3FFC3A66@ucsd.edu>
 <CABdHhvEQqx0yJ_b2cwt5iO+azCLqCdMck_v0HDHT0v5FBqOd1g@mail.gmail.com>
 <A63CB03F-000C-4A80-B8F9-621A075F6F6D@ucsd.edu>
 <CABdHhvGJm5CCObSQ+4VqP10TMM5b220GzWyZZJD+66xOOYPrtQ@mail.gmail.com>
Message-ID: <58593D6B-9473-4593-8E3E-EFDE174FF868@ucsd.edu>



> On Jun 8, 2018, at 2:15 PM, Hadley Wickham <h.wickham at gmail.com> wrote:
> 
> On Fri, Jun 8, 2018 at 2:09 PM, Berry, Charles <ccberry at ucsd.edu> wrote:
>> 
>> 
>>> On Jun 8, 2018, at 1:49 PM, Hadley Wickham <h.wickham at 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 = )                 2.8?s   3.54?s   3.29?s   34.9?s
> #> 2 list(x = quote(expr = ))    169ns 219.38ns    181ns   24.2?s
> 
> (note the units)

Yes. That is good for about half the difference. And I guess the rest is getting rid of seq(). This seems a bit quicker than anything else and satisfies Herve's objections:

subset_ROW <-
      function(x,i)
  {
      dims <- dim(x)
      nd <- length(dims)
      index_list <- if (nd > 1) 2L + 2L:nd else 0
      mc <- quote(x[i])
      mc[ index_list ] <- list(quote(expr=))
      mc[[ "drop" ]] <- FALSE
      eval(mc)
  }

Chuck


[Rd] Subsetting the "ROW"s of an object
Berry, Charles