[Rd] dget() much slower in recent R versions

[Hervé Pagès]

On 06/21/2014 12:56 AM, Prof Brian Ripley wrote:
> On 20/06/2014 15:37, Ista Zahn wrote:
>> Hello,
>>
>> I've noticed that dget() is much slower in the current and devel R
>> versions than in previous versions. In 2.15 reading a 10000-row
>> data.frame takes less than half a second:
>>
>>> (which.r <- R.Version()$version.string)
>> [1] "R version 2.15.2 (2012-10-26)"
>>> x <- data.frame(matrix(sample(letters, 100000, replace = TRUE), ncol
>>> = 10))
>>> dput(x, which.r)
>>> system.time(y <- dget(which.r))
>>     user  system elapsed
>>    0.546   0.033   0.586
>>
>> While in 3.1.0 and r-devel it takes around 7 seconds.
>>
>>> (which.r <- R.Version()$version.string)
>> [1] "R version 3.1.0 (2014-04-10)"
>>> x <- data.frame(matrix(sample(letters, 100000, replace = TRUE), ncol
>>> = 10))
>>> dput(x, which.r)
>>> system.time(y <- dget(which.r))
>>     user  system elapsed
>>    6.920   0.060   7.074
>>
>>> (which.r <- R.Version()$version.string)
>> [1] "R Under development (unstable) (2014-06-19 r65979)"
>>> x <- data.frame(matrix(sample(letters, 100000, replace = TRUE), ncol
>>> = 10))
>>> dput(x, which.r)
>>> system.time(y <- dget(which.r))
>>     user  system elapsed
>>    6.886   0.047   6.943
>>>
>>
>> I know dput/dget is probably not the right tool for this job:
>> nevertheless the slowdown in quite dramatic so I thought it was worth
>> calling attention to.
>
> This is completely the wrong way to do this. See ?dump.
>
> dget() basically calls eval(parse()).  parse() is much slower in R >=
> 3.0 mainly because it keeps more information.  Using keep.source=FALSE
> here speeds things up a lot.
>
>  > system.time(y <- dget(which.r))
>     user  system elapsed
>    3.233   0.012   3.248
>  > options(keep.source=FALSE)
>  > system.time(y <- dget(which.r))
>     user  system elapsed
>    0.090   0.001   0.092

Nice. But why add the 'keep.source' arg do dget() in R-devel rev 65990:

   dget <- function(file, keep.source = FALSE)
       eval(parse(file = file, keep.source = FALSE))

(Note that the 'keep.source' arg is actually ignored.)

Why not just:

   dget <- function(file)
       eval(parse(file = file, keep.source = FALSE))

Cheers,

H.