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

[Prof Brian Ripley]

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


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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