1) Unless you know what you are doing, you don't want to use it since
the speed advantage is small at best.
2) Suppose you want the median of 2n+1 values. Then all you need is a
value with n others to the left and n to the right. That is a
partially sorted vector. Example
set.seed(123)
x <- round(runif(11), 3)
sort.int(x, partial=6)
[1] 0.046 0.288 0.409 0.457 0.528 0.551 0.788 0.892 0.940 0.883 0.957
Thare are 5 values on each side of 0.551, but the ones on the right
are not sorted.
Now timings:
set.seed(123)
system.time(for(i in 1:1e5) sort.int(round(runif(11), 3)))
set.seed(123)
system.time(for(i in 1:1e5) sort.int(round(runif(11), 3), partial=6))
Try it for yourself, but remember this is a normally a tiny part of a
real problem and that specifying even 10% of the quantiles can be
slower than a full sort.
On Wed, 14 Jan 2009, rkevinbur...@charter.net wrote:
This is definitely a newbie question but from the documentation I have not been
able to figure out what the partial sort option on the sort method does. I have
read and re-read the documentation and looked at the examples but for some
reason it doesn't register. Would someone attempt to explain what sort with a
non-null partial array of indices does?
Thank you.
Kevin
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--
Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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