R help - Feb 2015 - How do I access a specific element of a multi-dimensional list

Dear list,

Let's say I have setup the following list:
a = c(2, 3, 5) 
b = c("aa", "bb", "cc") 
c = c(TRUE, FALSE, TRUE) 

x = list(a, b, c)

I want to access the first second dimension element of each first dimension 
element so that the result is something like:
(2, "aa", TRUE)

In my real life problem the list is about 350 elements in the first dimension 
so the solution must handle that.

Sincerely
Knut Hansen

try this:
> a = c(2, 3, 5)
>  b = c("aa", "bb", "cc")
>  c = c(TRUE, FALSE, TRUE)
>
>  x = list(a, b, c)
> x
[[1]]
[1] 2 3 5
[[2]]
[1] "aa" "bb" "cc"
[[3]]
[1]  TRUE FALSE  TRUE
> sapply(x, '[[', 1)
[1] "2"    "aa"   "TRUE"
>
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.


On Fri, Feb 20, 2015 at 7:18 AM, Knut Hansen <knut.hansen at uit.no>
wrote:
> Dear list,
>
> Let's say I have setup the following list:
> a = c(2, 3, 5)
> b = c("aa", "bb", "cc")
> c = c(TRUE, FALSE, TRUE)
>
> x = list(a, b, c)
>
> I want to access the first second dimension element of each first dimension
> element so that the result is something like:
> (2, "aa", TRUE)
>
> In my real life problem the list is about 350 elements in the first
dimension
> so the solution must handle that.
>
> Sincerely
> Knut Hansen
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

Hi,

  Jim's answer is neat.  There is an issue on the result.  All are
characters even though some are numeric or logic.  The following
implementation retains the variable type.
> x
[[1]]
[1] 2 3 5

[[2]]
[1] "aa" "bb" "cc"

[[3]]
[1]  TRUE FALSE  TRUE
> getFirst
function(aList)
{
  result <- list()
  for (i in 1:length(aList))
  {
    result <- c(result, aList[[i]][1])
  }
  return(result)
}
> getFirst(x)
[[1]]
[1] 2

[[2]]
[1] "aa"

[[3]]
[1] TRUE
> 


--
View this message in context:
http://r.789695.n4.nabble.com/How-do-I-access-a-specific-element-of-a-multi-dimensional-list-tp4703596p4703622.html
Sent from the R help mailing list archive at Nabble.com.