[R] Extracting multiple elements from a list
For a long time I've wanted a way to conveniently extract multiple elements from a list, which [[ doesn't allow. Can anyone suggest an efficient function to do this? Wouldn't it be a sensible addition to R? For example, alist - list() alist[[1]] - list() alist[[1]]$name - first alist[[1]]$vec - 1:4 alist[[2]] - list() alist[[2]]$name - second alist[[2]]$vec - 5:8 both.vec - c(alist[[1]]$vec, alist[[2]]$vec) Can I get both.vec without c() or an explicit loop? and new.names - c(one, two) alist[[1]]$name - new.names[1] alist[[2]]$name - new.names[2] Could I assign the new values in a quasi-vectorized way? Thanks, Scott Waichler Pacific Northwest National Laboratory Richland, WA USA __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
RE: [R] Extracting multiple elements from a list
Aren't sapply()/lapply() sufficient for this?
sapply(alist, function(x) x$vec)
[,1] [,2]
[1,]15
[2,]26
[3,]37
[4,]48
lapply(alist, function(x) x$vec)
[[1]]
[1] 1 2 3 4
[[2]]
[1] 5 6 7 8
HTH,
Andy
From: Waichler, Scott R
For a long time I've wanted a way to conveniently extract
multiple elements
from a list, which [[ doesn't allow. Can anyone suggest an efficient
function to do this? Wouldn't it be a sensible addition to R?
For example,
alist - list()
alist[[1]] - list()
alist[[1]]$name - first
alist[[1]]$vec - 1:4
alist[[2]] - list()
alist[[2]]$name - second
alist[[2]]$vec - 5:8
both.vec - c(alist[[1]]$vec, alist[[2]]$vec)
Can I get both.vec without c() or an explicit loop?
and
new.names - c(one, two)
alist[[1]]$name - new.names[1]
alist[[2]]$name - new.names[2]
Could I assign the new values in a quasi-vectorized way?
Thanks,
Scott Waichler
Pacific Northwest National Laboratory
Richland, WA USA
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RE: [R] Extracting multiple elements from a list
[] works on a list and extracts multiple elements. However, that is not
it seems what you want, rather, unions of elements of elements of lists.
That is a pretty unusual need, and perhaps you could explain you you need
it.
Andy's solution still need something like
do.call(c, lapply(alist, function(x) x$vec))
but then it *is* unions of elements of elements of lists.
On Thu, 15 Jan 2004, Liaw, Andy wrote:
Aren't sapply()/lapply() sufficient for this?
sapply(alist, function(x) x$vec)
[,1] [,2]
[1,]15
[2,]26
[3,]37
[4,]48
lapply(alist, function(x) x$vec)
[[1]]
[1] 1 2 3 4
[[2]]
[1] 5 6 7 8
HTH,
Andy
From: Waichler, Scott R
For a long time I've wanted a way to conveniently extract
multiple elements
from a list, which [[ doesn't allow. Can anyone suggest an efficient
function to do this? Wouldn't it be a sensible addition to R?
For example,
alist - list()
alist[[1]] - list()
alist[[1]]$name - first
alist[[1]]$vec - 1:4
alist[[2]] - list()
alist[[2]]$name - second
alist[[2]]$vec - 5:8
both.vec - c(alist[[1]]$vec, alist[[2]]$vec)
Can I get both.vec without c() or an explicit loop?
and
new.names - c(one, two)
alist[[1]]$name - new.names[1]
alist[[2]]$name - new.names[2]
Could I assign the new values in a quasi-vectorized way?
Thanks,
Scott Waichler
Pacific Northwest National Laboratory
Richland, WA USA
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Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UKFax: +44 1865 272595
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Re: [R] Extracting multiple elements from a list
For the first case, I actually do this pretty often and usually use something like: as.vector(sapply(alist, [[, vec)) For the second case, I think you just need to use lapply(): alist - lapply(seq(along = alist), function(i) alist[[i]]$name - new.names[i]) -roger Waichler, Scott R wrote: For a long time I've wanted a way to conveniently extract multiple elements from a list, which [[ doesn't allow. Can anyone suggest an efficient function to do this? Wouldn't it be a sensible addition to R? For example, alist - list() alist[[1]] - list() alist[[1]]$name - first alist[[1]]$vec - 1:4 alist[[2]] - list() alist[[2]]$name - second alist[[2]]$vec - 5:8 both.vec - c(alist[[1]]$vec, alist[[2]]$vec) Can I get both.vec without c() or an explicit loop? and new.names - c(one, two) alist[[1]]$name - new.names[1] alist[[2]]$name - new.names[2] Could I assign the new values in a quasi-vectorized way? Thanks, Scott Waichler Pacific Northwest National Laboratory Richland, WA USA __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Re: [R] Extracting multiple elements from a list
Sorry, that second example should be
alist - lapply(seq(along = alist), function(i) {
alist[[i]]$name - new.names[i])
alist
})
-roger
Roger D. Peng wrote:
For the first case, I actually do this pretty often and usually use
something like:
as.vector(sapply(alist, [[, vec))
For the second case, I think you just need to use lapply():
alist - lapply(seq(along = alist), function(i)
alist[[i]]$name - new.names[i])
-roger
Waichler, Scott R wrote:
For a long time I've wanted a way to conveniently extract multiple
elements
from a list, which [[ doesn't allow. Can anyone suggest an efficient
function to do this? Wouldn't it be a sensible addition to R?
For example,
alist - list()
alist[[1]] - list()
alist[[1]]$name - first
alist[[1]]$vec - 1:4
alist[[2]] - list()
alist[[2]]$name - second
alist[[2]]$vec - 5:8
both.vec - c(alist[[1]]$vec, alist[[2]]$vec)
Can I get both.vec without c() or an explicit loop?
and
new.names - c(one, two)
alist[[1]]$name - new.names[1]
alist[[2]]$name - new.names[2]
Could I assign the new values in a quasi-vectorized way?
Thanks,
Scott Waichler
Pacific Northwest National Laboratory
Richland, WA USA
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RE: [R] Extracting multiple elements from a list
Brian described well the operation I would like to do.
I'm not familiar with do.call() but I'll work on that.
Yes, ideally I would like to access values throughout a list object
with fully implict indexing, such as the invalid alist[[1:2]]$vec[c(2, 4)].
Notice I was hoping to subset anywhere in the data structure.
Since I can't do this subsetting with indexing directly, I was looking for
handy (and hopefully fast) functions that could be defined
generically and then called with arguments. The use of sapply()
and lapply() with function(i) seem promising, but do not quite
cover the functionality I was looking for.
The basic application of sapply() suggested by Andy
is fine but I can't access part of the second-level list, only the whole
vector. Roger's use of sapply()
as.vector(sapply(alist, [[, vec))
is a nice way to get the whole vector also, and I appreciate learning
that syntax. The correction by Roger for his use of lapply() still isn't
right though (see below).
alist - lapply(seq(along = alist), function(i) {
alist[[i]]$name - new.names[i]
alist
})
I desire:
alist
[[1]]
[[1]]$name
[1] one
[[1]]$vec
[1] 1 2 3 4
[[2]]
[[2]]$name
[1] two
[[2]]$vec
[1] 5 6 7 8
Roger's use of lapply() give:
alist
[[1]]
[[1]][[1]]
[[1]][[1]]$name
[1] one
[[1]][[1]]$vec
[1] 1 2 3 4
[[1]][[2]]
[[1]][[2]]$name
[1] two
[[1]][[2]]$vec
[1] 5 6 7 8
[[2]]
[[2]][[1]]
[[2]][[1]]$name
[1] one
[[2]][[1]]$vec
[1] 1 2 3 4
[[2]][[2]]
[[2]][[2]]$name
[1] two
[[2]][[2]]$vec
[1] 5 6 7 8
-Original Message-
From: Roger D. Peng [mailto:[EMAIL PROTECTED]
Sent: Thursday, January 15, 2004 12:24 PM
To: Waichler, Scott R
Cc: [EMAIL PROTECTED]
Subject: Re: [R] Extracting multiple elements from a list
Sorry, that second example should be
alist - lapply(seq(along = alist), function(i) {
alist[[i]]$name - new.names[i])
alist
})
-roger
Roger D. Peng wrote:
For the first case, I actually do this pretty often and usually use
something like:
as.vector(sapply(alist, [[, vec))
For the second case, I think you just need to use lapply():
alist - lapply(seq(along = alist), function(i)
alist[[i]]$name - new.names[i])
-roger
Waichler, Scott R wrote:
For a long time I've wanted a way to conveniently extract multiple
elements
from a list, which [[ doesn't allow. Can anyone suggest
an efficient
function to do this? Wouldn't it be a sensible addition to R?
For example,
alist - list()
alist[[1]] - list()
alist[[1]]$name - first
alist[[1]]$vec - 1:4
alist[[2]] - list()
alist[[2]]$name - second
alist[[2]]$vec - 5:8
both.vec - c(alist[[1]]$vec, alist[[2]]$vec)
Can I get both.vec without c() or an explicit loop?
and
new.names - c(one, two)
alist[[1]]$name - new.names[1]
alist[[2]]$name - new.names[2]
Could I assign the new values in a quasi-vectorized way?
Thanks,
Scott Waichler
Pacific Northwest National Laboratory
Richland, WA USA
__
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Re: [R] Extracting multiple elements from a list
Waichler, Scott R wrote: Brian described well the operation I would like to do. I'm not familiar with do.call() but I'll work on that. Yes, ideally I would like to access values throughout a list object with fully implict indexing, such as the invalid alist[[1:2]]$vec[c(2, 4)]. Notice I was hoping to subset anywhere in the data structure. Since I can't do this subsetting with indexing directly, I was looking for handy (and hopefully fast) functions that could be defined generically and then called with arguments. The use of sapply() and lapply() with function(i) seem promising, but do not quite cover the functionality I was looking for. The functions sapply() and lapply() have more generality that has been overlooked in this thread. This will answer your first question. unlist(lapply(alist, function(x, ind = c(2,4)) x$vec[ind])) [1] 2 4 6 8 hth, Julian -- --- Julian Taylor phone: +61 8 8303 6751 ARC Research Associatefax: +61 8 8303 6760 BiometricsSA, mobile: +61 4 1638 8180 University of Adelaide/SARDIemail: [EMAIL PROTECTED] Private Mail Bag 1www: http://www.BiometricsSA.adelaide.edu.au Glen Osmond SA 5064 There is no spoon. -- Orphan boy --- __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
