[R] lapply, strsplit, and list elements

[William Dunlap]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Dick Harray
> Sent: Friday, February 04, 2011 7:37 AM
> To: r-help at r-project.org
> Subject: [R] lapply, strsplit, and list elements
> 
> Hi there,
> 
> I have a problem about lapply, strsplit, and accessing list elements,
> which I don't understand or cannot solve:
> 
> I have e.g. a character vector with three elements:
> 
> x = c("349/077,349/074,349/100,349/117",
>          "340/384.2,340/513,367/139,455/128,D13/168",
>          "600/437,128/903,128/904")
> 
> 	
> The task I want to perform, is to generate a list, comprising the
> portion in front of the "/" of each element of x:
> 
> neededResult = list(c("349","349", "349", "349"),
>                              c("340", "340", "367", "455", "D13"),
>                              c("600", "128", "128") )

Try the following, which first splits each string by commas
(returning a list), then removes the first slash and everything
after it (using lapply to maintain the list structure).

   > gotResult <- lapply(strsplit(x, ","), function(xi)gsub("/.*", "",
xi))
   > identical(getResult, neededResult)
   [1] TRUE

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

> 
> 
> I figured out that for a single element of x the following works
> 
> unlist( lapply( strsplit( unlist( strsplit(x[1], "\\,") ), 
> "/"), "[", 1) )
> 
> but due to "unlist" it doesn't provide the required result if extended
> to all elements of x
> 
> unlist(lapply(strsplit( unlist( lapply(x, strsplit, "\\,")), 
> "/"), "[",))
> 
> 
> Someone can help me to get the needed result?
> 
> Thanks and regards,
> 
> Dirk
> 
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