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putting output from print() into a string?

5 messages · David Firth, Uwe Ligges, Peter Dalgaard +1 more

David Firth
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Is there some neat way of storing the printed representation of an 
object as a character string?  I can see how it could be done via 
disk using sink() and then scan(), but that's ugly.

Something like Lisp-Stat's "with-output-to-string" macro perhaps?



David Firth                        Phone +44 1865 278544
Nuffield College                   Fax   +44 1865 278621
Oxford OX1 1NF                     Secretary +44 1865 278612
United Kingdom                     Email david.firth at nuffield.oxford.ac.uk

http://www.stats.ox.ac.uk/~firth/
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Uwe Ligges
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On Sun, 12 Nov 2000, David Firth wrote:

            

      
      
      
    

        
dump() ?

Uwe Ligges

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      Peter Dalgaard
    

    

      
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Uwe Ligges <ligges at statistik.uni-dortmund.de> writes:

            

      
      
      
    

        
I don't think that was what David was looking for. If you really want
to postprocess the printed output, the sink-then-scan method would
seem to be the way to do it (or the soon-to- be readLines() instead of
scan()). I suppose that a sink(text=...) could be implemented, but
AFAIK it is not on anyones TODO list. 

One obvious counterquestion is "Why?". It would normally be preferable
to retrieve information from the object itself rather than the printed
representation, which is generally lossful in a number of ways.

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      David Firth
    

    

      
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That's right, dump() doesn't do what I want: I should have made it 
clearer that what I would like to store in a string is the 
prettily-printed representation that gets displayed on the console 
when print() is called.  Yes, sink()-ing to a string would be nice. 
Or perhaps (more radically?) an optional argument as in print(mydata, 
return.the.string=TRUE) which requests the return of a string instead 
of returning the object mydata itself.

            

      
      
      
    

        
I somehow thought I'd be asked this!  I need to exchange information 
rapidly with a non-R user using write.socket(), and for that purpose 
the information has to be in the form of a character string.  I can 
of course format the string myself using formatC(), paste(), etc., 
but it turns out that the way that data frames get formatted by 
print.matrix() is just right for my purposes.  So, rather than 
duplicate some of the excellent work that went into print.matrix(), 
I'd like to use it!

Thanks anyway for your very helpful answer, Peter: at least I can 
stop looking now.

Regards -- David

            

      
      
      
    

        
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      Brian Ripley
    

    

      
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On 12 Nov 2000, Peter Dalgaard BSA wrote:

        

            

      
      
      
    

        
Sure it is.  Output connections to a character vector solves this, I
believe. I have had a prototype running, but doubt if this will make 1.2.
Indeed, I suspect what David really wants is a socket as an output
connection.  (`Connections' are S4-speak for general hooks for input and
output streams.)

Brian