What do you want the compressed R object to be? (It is not an R
object.)
Omegahat package Rcompression may help you, but it returns a raw
vector (and that has overheads such as the header: you could use its
length if appropriate).
On Sat, 7 Feb 2009, Markus Loecher wrote:
This might seem like a strange question
It is ore than a little imprecise ....
but is there any way to compress an
R object (such as a matrix) and know its resulting size in bytes ?
Clearly, I could implement this in the following way (if x is my matrix):
zz <- gzfile(fname,"w");
write.table(x,zz);
close(zz);
file.info(fname)[,"size"];
Hmm, that calcuates the size of a compressed character representation
of the object. So do you want the size of an object or of its
character representation? object.size() calculated the first.
However, I need to do this for hundreds of thousands of objects and the
overhead in terms of disk access due to the actual file creation is
prohibitive.
The overheads of finding a character representation and of allocating
an R object for the result would also be large.
I guess, I would like a modified object.size() function that returns the
size of the compressed (e.g. gzip) version of the object.
I don't see the pooint of calculating the size of something you will
not use. And anything involving 'hundreds of thousands of objects' is
better done in C code. So why not just write a C function to do
whatever it is you really want (but have not told us).
In fact ehe way lazy-loading is implemented is pretty close to what
you describe -- that uses an on-disk database and it not slow for
100,000 objects.
Thanks!
Markus
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Brian D. Ripley, rip...@stats.ox.ac.uk
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