[R-sig-hpc] Question about output the objects on slave by SNOW

[Stephen Weston]

'cat' and 'print' work from the workers, but the
output is redirected to /dev/null (or NUL:) by
default.  If you set the 'outfile' option to an
empty string when creating the cluster object,
then output won't be redirected in the workers,
and will generally be displayed in your session.

For example:

> f <- function(iter,x) {
+   y <- sin(x)
+   cat('x=', x,'\n')
+   return(y)
+ }
> library(snow)
> cl <- makeSOCKcluster(2, outfile="")
starting worker for localhost:10187
starting worker for localhost:10187
> clusterExport(cl, ls())
Type: EXEC
Type: EXEC
Type: EXEC
Type: EXEC
>
> parSapply(cl,1:2,f,1)
Type: EXEC
x= 1
Type: EXEC
x= 1
[1] 0.841471 0.841471


The output can be a bit jumbled, and it includes
other output generated by the workers, but I find it
very useful for debugging.

- Steve



On Fri, Mar 16, 2012 at 12:23 PM, Libo Sun <libosun at rams.colostate.edu> wrote:
> Hi all,
>
> I am using SNOW package on my multi-core Windows machine. I am wondering if
> there is a way to output the objects on slave, as far as I know 'cat' or
> 'print' doesn't work. One simple example:
>
>> f<-function(iter,x) {
> + y=sin(x)
> + cat('x=', x,'\n')
> + return(y)
> + }
>>
>> library(snow)
>> cl<-makeCluster(2)
>> clusterExport(cl,ls())
>>
>> parSapply(cl,1:2,f,1)
> [1] 0.841471 0.841471
>>
>
> I would like to get the information about 'x', like this,
>
>> sapply(1:2,f,1)
> x= 1
> x= 1
> [1] 0.841471 0.841471
>>
>
> Thanks,
> Libo
>
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