[R] Does R always insist on sending plot output to a file?

[Matt Shotwell]

Donald,

At least for the PDF device (I know you asked about png, but I believe
they are similar), the answer no. Ultimately, this device calls the
standard C function fopen, and writes its data to the resulting file
stream.

If you're using GNU Linux, you might trick R into writing to a fifo (a
named pipe, see 'man fifo'), or some other in-memory device, and read
from it with another program. My initial experiments with this, however,
were not successful.

A better solution here, would be to have the various graphics devices
write to an R connection, as do most other R functions that input and
output data. In this way, we could write graphics data to a RAW
connection (rawConnection()), which is essentially a memory buffer. 

There are two obvious barriers to this:
1. C level I/O routines (e.g. fprintf) are heavily integrated into the
graphics device code. Hence, accommodating R connections would require
significant changes.
2. The graphics devices are mostly implemented in C, and there is (at
present) no interface to R connections at the C level.

-Matt

On Wed, 2010-08-18 at 21:49 -0400, Donald Paul Winston wrote:
> I need to write the output of a R plot to a Java OutputStream. It looks like
> R insists on sending it's output to a file. Is there anyway to get bytes
> directly from the output of a plot so I can write it with Java? Writing it
> to a file is too slow.
> 
> Is there a parameter in the graphics device function png(..) that directs
> output to a variable in memory? 
> 
> x <- plot(.)  would make sense.

-- 
Matthew S. Shotwell
Graduate Student 
Division of Biostatistics and Epidemiology
Medical University of South Carolina