R help - Jul 2010 - Subsetting Lists

I am looking for a way to create a vector which contains the second element of 
every vector in the list. However, not every vector has two components, so I 
need to generate an NA for those missing. For example, I have created the 
following list:

lst <- list(c("a", "b"), c("c"),
c("d", "e"), c("f", "g"))
> lst
[[1]]
[1] "a" "b"
[[2]]
[1] "c"
[[3]]
[1] "d" "e"
[[4]]
[1] "f" "g"

I would like the output to be the following:
> output
[1] "b"   NA "e"   "g"

I know I can accomplish this using a for loop, but I am wondering if there's
a
simple and neat way of getting this done in one step?

Thanks in advance.

- Andrew


      
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Hi Andrew,

Try

sapply(lst, "[", 2)

HTH,
Jorge


On Mon, Jul 12, 2010 at 3:12 PM, Andrew Leeser <> wrote:
> I am looking for a way to create a vector which contains the second element
> of
> every vector in the list. However, not every vector has two components, so
> I
> need to generate an NA for those missing. For example, I have created the
> following list:
>
> lst <- list(c("a", "b"), c("c"),
c("d", "e"), c("f", "g"))
>
> > lst
> [[1]]
> [1] "a" "b"
> [[2]]
> [1] "c"
> [[3]]
> [1] "d" "e"
> [[4]]
> [1] "f" "g"
>
> I would like the output to be the following:
>
> > output
> [1] "b"   NA "e"   "g"
>
> I know I can accomplish this using a for loop, but I am wondering if
> there's a
> simple and neat way of getting this done in one step?
>
> Thanks in advance.
>
> - Andrew
>
>
>
>        [[alternative HTML version deleted]]
>
>
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>
>
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