[R] How to fetch specific part from a number of Text files?

[Charles C. Berry]

On Mon, 15 Dec 2008, megh wrote:

>
> Hi all,
>
> I my c: drive I have possibly 1,000 notepad files, with .txt extension. They
> are named as the dates on which they were saved i.e. 1st file name is
> "Volume_4-18-2008", 2nd one is "Volume_4-21-2008", 3rd one
> "Volume_4-22-2008" and so on............
>
> Also, content of each file are in same format like :
>
> ******** content of 1st file *************
> section : 1
> -----       ---------      ----------    -----------
> -----       ---------      ----------    -----------
> -----       ---------      ----------    -----------
> -----       ---------      ----------    -----------
> section : 2
> -----       ---------      ----------    -----------
> -----       ---------      ----------    -----------
> -----       ---------      ----------    -----------
> -----       ---------      ----------    -----------
> section : 3
> -----       ---------      ----------    -----------
> -----       ---------      ----------    -----------
> -----       ---------      ----------    -----------
> -----       ---------      ----------    -----------
> section : 4
> -----       ---------      ----------    -----------
> -----       ---------      ----------    -----------
> -----       ---------      ----------    -----------
> -----       ---------      ----------    -----------
>
> Here all files have 4-sections, just like shown here but contents within
> each section (i.e. dashed line here) differs file to file.
>
> What I have to do is I have to fetch contents of "section : 2" from each
> file and then save it to a R-object, matrix of list for further analysis.
>
> Can you ppl please tell me how to do that?

Here is the outline:

 	*) use list.files() or Sys.glob() to get a list of the files

 	*) write a function that takes the file name as its arg, uses
            readLines() to swallow the text and uses grep() to find the
            'section' lines. Then put the 'dashes' in between two section
            lines into a separate object (say, dash.lines). Then use

 		as.matrix( read.table(con <- textConnection( dash.lines ) )
 		close(con)

 	  to get the numeric values or maybe

 		sapply( strsplit(dash.lines, "[ ]+"), as.numeric)

 	*) debug this on one file


 	*) use lapply  to step thru the list of file names.

See

 	?list.files
 	?Sys.glob
 	?readLines
 	?grep
 	?textConnection
 	?strsplit
 	?sapply

HTH,

Chuck


>
> Thanks and regards,
> -- 
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>
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Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901