On 04/01/2014 10:17 AM, Ryan wrote:
That won't work if any vector has fewer than 5 elements. Maybe
lapply(x, head, n=5)
would work?
Yes. Note that you can use endoapply() to preserve the class of the
original object:
> endoapply(cvg, head, n=5)
RleList of length 3
$chr1
integer-Rle of length 5 with 2 runs
Lengths: 4 1
Values : 1 2
$chr2
integer-Rle of length 5 with 4 runs
Lengths: 1 1 1 2
Values : 0 1 2 3
$chr3
integer-Rle of length 5 with 1 run
Lengths: 5
Values : 0
But lapply- or endoapply-based solutions are slower than a [ based
solution. Unfortunately the latter requires too much munging to get
the subscript right:
## parallel seq_len()
pseq_len <- function(eltlens)
{
ans_skeleton <- PartitioningByWidth(eltlens)
tmp <- relist(seq_len(sum(eltlens)), ans_skeleton)
tmp - start(ans_skeleton) + 1L
}
Then:
> pseq_len(c(5, 1, 0, 2))
IntegerList of length 4
[[1]] 1 2 3 4 5
[[2]] 1
[[3]] integer(0)
[[4]] 1 2
> cvg[pseq_len(pmin(elementLengths(cvg), 5))]
RleList of length 3
$chr1
integer-Rle of length 5 with 2 runs
Lengths: 4 1
Values : 1 2
$chr2
integer-Rle of length 5 with 4 runs
Lengths: 1 1 1 2
Values : 0 1 2 3
$chr3
integer-Rle of length 5 with 1 run
Lengths: 5
Values : 0
H.
On Tue Apr 1 09:24:51 2014, Cook, Malcolm wrote:
in the mean time,
lapply(`[`,x,IntegerList(1:5))
??
>-----Original Message-----
>From: bioc-devel-boun...@r-project.org
[mailto:bioc-devel-boun...@r-project.org] On Behalf Of Michael Lawrence
>Sent: Tuesday, April 01, 2014 9:21 AM
>To: bioc-devel@r-project.org
>Subject: [Bioc-devel] Subsetting Lists by Lists
>
>Mostly to Herve:
>
>Sometimes we want to pluck the first 1, or 10, or whatever elements
from
>each element of a list. If I had a list 'x', I thought I could do
this with:
>
>x[IntegerList(1:5)]
>
>But it only gives elements 1:5 from x[[1]], not each element of
'x'. In
>other words, I thought the index would be repped out. Instead, 'x' is
>subset to the length of 'i', and I'm not sure if that makes sense?
>
>But maybe what we really want are pluckHead/Tail, which would be
robust to
>the case that < n elements are in an element. And of course a more
general
>pluck(x, i) to select 'i' from each element, but I wanted the line
above to
>do that.
>
>Michael
>
> [[alternative HTML version deleted]]
>
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Program in Computational Biology
Division of Public Health Sciences
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