[R] lapply, strsplit, and list elements

[Greg Snow]

Try this:

> 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")
> 
> library(gsubfn)
> out <- strapply(x, '([0-9]+)(?=/)')
> out
[[1]]
[1] "349" "349" "349" "349"

[[2]]
[1] "340" "340" "367" "455" "13" 

[[3]]
[1] "600" "128" "128"


The strapply looks for the pattern then returns every time it finds the pattern.  The pattern in this case is 1 or more digits that are followed by a /, but the slash is not included in the matched portion (a positive look ahead).

If you need more than digits you can modify the pattern to whatever matches before the /.

Hope this helps,

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111


> -----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 8:37 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") )
> 
> 
> 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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