Or
rapply(l,function(x) x[1])
#[1] 1 3 7
set.seed(42)
l1 <- replicate(1e6, list(sample(1:5,sample(8),replace=T)))
system.time(r1 <- sapply(l1, `[`, 1))
# user system elapsed
# 1.324 0.000 1.326
system.time(r2 <- rapply(l1, function(x) x[1]))
# user system elapsed
# 0.736 0.004 0.741
identical(r1,r2)
#[1] TRUE
system.time({
eltlens <- elementLengths(l1)
r3 <- unlist(l1, use.names=FALSE)[cumsum(eltlens) - eltlens + 1L]
})
# user system elapsed
# 0.153 0.000 0.154
A.K.
On Tuesday, July 22, 2014 12:11 AM, Richard M. Heiberger <r...@temple.edu>
wrote:
l = list(c(1,2), c(3,5,6), c(7))
sapply(l, `[`, 1)
On Mon, Jul 21, 2014 at 3:55 PM, carol white <wht_...@yahoo.com> wrote:
> Hi,
> If we have a list of vectors of different lengths, how is it possible to
> retrieve the first element of the vectors of the list?
>
>
> l = list(c(1,2), c(3,5,6), c(7))
>
> 1,3,7 should be retrieved
>
> Thanks
>
> Carol
> [[alternative HTML version deleted]]
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
______________________________________________
R-help@r-project.org mailing list
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.
