selecting a subset of files to be processed

Dear R People:

I am using a Linux system in which I have about 3000 files.

I would like to randomly select about 45 of those files to be processed in R.

Could I make the selection in R or should I do it in Linux, please?

This is with R-2.15.1.

Thanks,
erin


--
Erin Hodgess
Associate Professor
Department of Computer and Mathematical Sciences
University of Houston - Downtown
mailto: erinm.hodgess at gmail.com

Dear R People:

I am using a Linux system in which I have about 3000 files.

I would like to randomly select about 45 of those files to be processed in R.

Could I make the selection in R or should I do it in Linux, please?

This is with R-2.15.1.

Thanks,
erin

Hello,

If the files are to be processed in R select a random sample in R.
Using list.files() you can assign a character vector with the filenames 
of interest and then sample from that vector.

?list.files
filenames <- list.files(path, pattern)

rand.sampl <- sample(filenames, 45)

Hope this helps,

Rui Barradas

Em 28-07-2012 18:49, Erin Hodgess escreveu:

Dear R People:

I am using a Linux system in which I have about 3000 files.

I would like to randomly select about 45 of those files to be processed in
R.

Could I make the selection in R or should I do it in Linux, please?

This is with R-2.15.1.

Thanks,
erin

And, in addition to the tip from Rui (and similar from Joshua) below,
I would advise that there is one good reason not to try doing it
in "pure Linux".

The only source (that I know of) in Linux itself for random numbers
can be tapped by something like

  cat /dev/random > filename

/dev/random stores noise generated by the timings of system events
(keyboard presses, mouse-clicks, disk accesses, interrupts, etc.)
after subjecting them to a high-entropy stirring process. See:

  man random

It yields them in the form of random bytes (each of 8 random 0/1 bits)
and you would have to devise some means of coverting those onto a
form suitable for accessing a directory listing at random. Not a
pretty task!

There is also the command 'rand' available in the openSSL toolkit,
but that still outputs the results in the same format as /dev/random.

If you really want to do this outside R, the I would suggest writing
a little C program (to be run from the Linux command line). C can
do its own random number generation, with results returned as
real (double), and then apply these to select at random from the
contents of a file generated by something like

  ls filesdir > filelist.txt

and output the random selection.

Ted.

On 28-Jul-2012 18:00:38 Rui Barradas wrote:

Hello,

If the files are to be processed in R select a random sample in R.
Using list.files() you can assign a character vector with the filenames
of interest and then sample from that vector.

?list.files
filenames <- list.files(path, pattern)

rand.sampl <- sample(filenames, 45)

Hope this helps,

Rui Barradas

Em 28-07-2012 18:49, Erin Hodgess escreveu:

Dear R People:

I am using a Linux system in which I have about 3000 files.

I would like to randomly select about 45 of those files to be processed in
R.

Could I make the selection in R or should I do it in Linux, please?

This is with R-2.15.1.

Thanks,
erin

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E-Mail: (Ted Harding) <Ted.Harding at wlandres.net>
Date: 28-Jul-2012  Time: 19:32:26
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