R help - Aug 2011 - Help: extrac the first entry for each component of a list

Dear All,
I would like to know, beside writing a function and then apply it to a list, or
using a for loop, whether there is a one-line command to do the following.
Suppose we have a list, each of whose components are
numeric:
> a <- vector("list",3)
> a[[1]] <-c(1,2)
> a[[2]] <-c(3,4)
> a[[3]] <- c(5,6)
> a
[[1]]
[1] 1 2

[[2]]
[1] 3 4

[[3]]
[1] 5 6

Target: I would like to extract from each of its components the first entry and
store them into a vector, ie, to extract 1 from a[[1]], 3 from a[[2]], 5 from
a[[3]], and store 1,3,5 into a vector without using for loops.
Thank you,
Chee
	[[alternative HTML version deleted]]

sapply(a, `[`, 1)

On Wed, Aug 24, 2011 at 12:18 AM, Chee Chen <chee.chen at yahoo.com>
wrote:
> Dear All,
> I would like to know, beside writing a function and then apply it to a
list, or using a for loop, whether there is a one-line command to do the
following.
> Suppose we have a list, each of whose components are numeric:
>> a <- vector("list",3)
>> a[[1]] <-c(1,2)
>> a[[2]] <-c(3,4)
>> a[[3]] <- c(5,6)
>> a
> [[1]]
> [1] 1 2
>
> [[2]]
> [1] 3 4
>
> [[3]]
> [1] 5 6
>
> Target: I would like to extract from each of its components the first entry
and store them into a vector, ie, to extract 1 from a[[1]], 3 from a[[2]], 5
from a[[3]], and store 1,3,5 into a vector without using for loops.
> Thank you,
> Chee
> ? ? ? ?[[alternative HTML version deleted]]
>
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