[R] Using Rscript to read from a file

[Dirk Eddelbuettel]

On 14 October 2010 at 11:21, Dirk Eddelbuettel wrote:
| On 14 October 2010 at 08:49, Saptarshi Guha wrote:
| | Hello,
| | I have this script which will be invoked as
| | 
| | Rscript a.r < a.r
| | 
| | a.r follows
| | 
| | #!/usr/bin/Rscript --vanilla
| | f=file("stdin")
| | while(TRUE){
| |     y=readLines(f,n=1,warn=TRUE)
| |   if(length(y)==0) break else print(y)
| | }
| | 
| | 
| | But it only reads one line from a.r
| | How can I read line by line from standard input?
| 
| If you can substitute in r (from littler) for Rscript, then you get proper
| behaviour.  Here is an old example from littler:
| 
|    $ ls -l /usr/bin | awk '!/^total/ {print $5}' | \
|        r -e 'fsizes <- as.integer(readLines()); print(summary(fsizes))' | \
|        tail -2
|     Min.  1st Qu.   Median     Mean  3rd Qu.     Max.
|        1     1720    10900   108000    39200 11100000
|    $
| 
| This uses awk to get the file size from ls, and then runs R's summary() over
| it.  For some reason, readLines() now echos back to the screen which is why I
| added the 'tail -2' at the end.

Got it. We changed something since we first created this example in 2006, and
we now need to set the -i flags.  So with that:

  $ ls -l /usr/bin | awk '!/^total/ {print $5}' | \
      r -i -e 'fsizes <- as.integer(readLines()); print(summary(fsizes))'
      Min.  1st Qu.   Median     Mean  3rd Qu.     Max. 
         1     1720    10900   108000    39200 11100000 
  $ 

Dirk


-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com