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readJPEG function cannot open jpeg files

12 messages · Jeff Newmiller, William Dunlap, Yi Yuan +5 more

Jeff Newmiller
# 
Being unable to open a file is a related to your operating system and how R interacts with that OS. If your interactive development environment (IDE, of which RStudio is an example) is trying to make things simpler for you but you don't understand how to use it, then you need to ask help from your RStudio support resources, not here.

When posting here, you should mention your results from using base R functions like

?sessionInfo
?getwd
?list.files

as indicated in the Posting Guide mentioned at the bottom of every R-help email.

Consistent with the fact that this is an interface issue between R and the OS, sometimes you will have to investigate the problem from outside R. For example, you might need to investigate issues with security permissions that are OS specific and completely outside the scope of this forum.
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Sent from my phone. Please excuse my brevity.
Yi Yuan <lambandme at gmail.com> wrote:

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Suzen, Mehmet
    

    

      
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Similar issue with URLs:

            

      
      
      
    

        
description
"http://upload.wikimedia.org/wikipedia/commons/9/9d/Barack_Obama.jpg"
                                                                class
                                                                "url"
                                                                 mode
                                                                  "r"
                                                                 text
                                                               "text"
                                                               opened
                                                             "closed"
                                                             can read
                                                                "yes"
                                                            can write
                                                                 "no"

            

      
      
      
    

        
Error in readJPEG(yesWeCan) :
  unable to open
http://upload.wikimedia.org/wikipedia/commons/9/9d/Barack_Obama.jpg

        
On 14 January 2013 14:57, Yi Yuan <lambandme at gmail.com> wrote:

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      William Dunlap
    

    

      
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You can use file.info("myFile") to make sure the file exists and has appropriate permissions ("mode"
in file.info's lingo, as in Unix).  E.g.,

            

      
      
      
    

        
size isdir mode mtime ctime atime  exe
c:/temp/BO.jpeg   NA    NA <NA>  <NA>  <NA>  <NA> <NA>

            

      
      
      
    

        
size isdir mode               mtime               ctime               atime
c:/temp/BO.jpg 150536 FALSE  666 2013-01-14 08:35:32 2013-01-14 08:33:09 2013-01-14 08:33:09
               exe
c:/temp/BO.jpg  no

I can readJPEG() the file with mode 666, but not all permission information is encoded in the mode. 

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        
      

    

    

      
      

        
      

    

    

      
      

        
      

    

    

      
      

        


  

        

      Brian Ripley
    

    

      
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On 14/01/2013 16:26, Suzen, Mehmet wrote:

            

      
      
      
    

        
Not a similar issue at all: a URL is not a file.  That most functions in 
R itself open connections including URLs does not mean that contributed 
packages do.  The package help is quite specific about its requirements.

   source: Either name of the file to read from or a raw vector
           representing the JPEG file content.

Which suggests to you how you can do this, apart from download.file, of 
course.  Something like

readJPEG(readBin(yesWeCan, "raw", 1e6))

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Duncan Murdoch
    

    

      
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On 13-01-14 11:59 AM, Yi Yuan wrote:

            

      
      
      
    

        
You seem to sometimes have spaces ahead of "home" and sometimes not.

What I recommend most people do on Windows is not to try to type the 
filename yourself, use file.choose() or choose.files() to get a dialog 
box and pick it out of there.

Duncan Murdoch

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Duncan Murdoch
    

    

      
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On 13-01-14 12:18 PM, Yi Yuan wrote:

            

      
      
      
    

        
Another recommendation I make for all Windows users is to change the 
Explorer options to display full filenames.  That would have prevented 
this error.  (This is an option in Windows, not in R.)

I've never understood why Microsoft thinks it is good to display 
incomplete filenames.  This practice causes so many problems.

Duncan Murdoch

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Suzen, Mehmet
    

    

      
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On 14 January 2013 18:56, Prof Brian Ripley <ripley at stats.ox.ac.uk> wrote:

            

      
      
      
    

        
Dear Prof. Ripley,

Thank you for the correction. I was thinking in the lines of
'Everything is a file' concept.
(http://en.wikipedia.org/wiki/Everything_is_a_file).

Best,
-m

  
  


  


      

    

    

      
      

        


  

        

      Rolf Turner
    

    

      
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On 01/15/2013 08:04 AM, Duncan Murdoch wrote:

        
<SNIP>

            

      
      
      
    

        
<SNIP>

Personally, I never understand "Why Microsoft?".

     cheers,

         Rolf Turner