[R] concatenate vector after strsplit()

[David Winsemius]

On Feb 20, 2011, at 11:13 AM, Robert Baer wrote:

> ls is a list of character vectors created by strsplit()
>
> I want to concatenate  the 1st 4 character elements of each list  
> item as a new vector called file.  I admit to being confused about  
> list syntax even after numerous readings.
>
> Here's what I tried:
>
> ls <- list(c("Focused", "10k", "A12", "t04.tif", "+", "µm"),  
> c("Focused",
> "10k", "A12", "t08.tif", "+", "µm"), c("Focused", "10k", "A12",
> "t12.tif", "+", "µm"), c("Focused", "10k", "A12", "t16.tif",
> "+", "µm"), c("Focused", "10k", "A12", "t20.tif", "+", "µm"),
>    c("Focused", "10k", "A12", "t24.tif", "+", "µm"), c("Focused",
>    "10k", "A12", "t36.tif", "+", "µm"), c("Focused", "10k",
>    "A12", "t48.tif", "+", "µm"), c("Focused", "10k", "B12",
>    "t04.tif", "+", "µm"), c("Focused", "10k", "B12", "t08.tif",
>    "+", "µm"))

Perhaps:

 > sapply(ls1, paste, collapse="")
  [1] "Focused10kA12t04.tif+µm" "Focused10kA12t08.tif+µm"
  [3] "Focused10kA12t12.tif+µm" "Focused10kA12t16.tif+µm"
  [5] "Focused10kA12t20.tif+µm" "Focused10kA12t24.tif+µm"
  [7] "Focused10kA12t36.tif+µm" "Focused10kA12t48.tif+µm"
  [9] "Focused10kB12t04.tif+µm" "Focused10kB12t08.tif+µm"

(I changed the name and will not illustrate its assignment to "file".  
It is generally considered poor programming practice  to use function  
names for variable objects.)
-- 
David.
>
> # Test the waters with one element
> cat(unlist(ls[1])[1:4])      # WHY DOES THE COMMAND PROMPT NOT  
> APPEAR ON NEXT LINE AS USUAL???
>
> # Appears to work except for command prompt glitch
>
> # Attempts to use tapply() don't get me anywhere
> file <- tapply(unlist(ls), list(1:length(unlist(ls))),  
> cat(unlist(ls[1])[1:4]))
>
> I'm grateful for an approach to putting my vector together, but I'd  
> also love to understand the headache I've apparently given the  
> command parser.  I'm apparently doing some "no no".
>
> Thanks,
>
> Rob
>
>> R.Version()
> $platform
> [1] "i386-pc-mingw32"
>
> $arch
> [1] "i386"
>
> $os
> [1] "mingw32"
>
> $system
> [1] "i386, mingw32"
>
> $status
> [1] ""
>
> $major
> [1] "2"
>
> $minor
> [1] "12.1"
>
> $year
> [1] "2010"
>
> $month
> [1] "12"
>
> $day
> [1] "16"
>
> $`svn rev`
> [1] "53855"
>
> $language
> [1] "R"
>
> $version.string
> [1] "R version 2.12.1 (2010-12-16)"
>
>
> 	[[alternative HTML version deleted]]
>
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David Winsemius, MD
West Hartford, CT