Here is an alternative solution
> foo <- array(data = rnorm(32), dim = c(4,4,2),
+ dimnames=list(letters[1:4], LETTERS[1:4], letters[5:6]))
>
> ind <- which(foo > 0, arr.ind = TRUE)
> row.names(ind) <- NULL ## to avoid warnings.
>
> mapply("[", dimnames(foo), data.frame(ind))
[,1] [,2] [,3]
[1,] "a" "A" "e"
[2,] "b" "A" "e"
[3,] "a" "B" "e"
[4,] "c" "B" "e"
[5,] "a" "C" "e"
[6,] "c" "C" "e"
[7,] "b" "D" "e"
[8,] "a" "A" "f"
[9,] "b" "B" "f"
[10,] "c" "B" "f"
[11,] "d" "B" "f"
[12,] "a" "C" "f"
[13,] "d" "C" "f"
[14,] "a" "D" "f"
[15,] "b" "D" "f"
Bill Venables.
-----Original Message-----
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
Behalf Of Dennis Murphy
Sent: Monday, 16 May 2011 3:14 PM
To: Pierre Roudier
Cc: r-help@r-project.org
Subject: Re: [R] Extracting the dimnames of an array with variable dimensions
Hi:
Does it have to be an array? If all you're interested in is the
dimnames, how about this?
library(plyr)
foo <- array(data = rnorm(32), dim = c(4,4,2),
dimnames=list(letters[1:4], LETTERS[1:4], letters[5:6]))
> foo
, , e
A B C D
a -0.2183877 -0.8912908 -2.0175612 -0.8080548
b 0.4870784 -0.8626293 -0.5641368 -0.5219722
c 0.8821044 0.3187850 1.2203297 -0.3151186
d -0.9894656 -1.1779108 0.9853935 0.3560747
, , f
A B C D
a 0.7357773 -1.7591637 1.6320887 1.2248529
b 0.4662315 0.1131432 -0.9790887 -0.6575306
c -0.3564725 -0.9202688 0.1017894 0.7382683
d 0.2825117 0.9242299 0.3577063 -1.3297339
# flatten array into a data frame with dimnames as factors
# adply() converts an array to a data frame, applying a function
# along the stated dimensions
u <- adply(foo, c(1, 2, 3), as.vector)
subset(u, V1 > 0)[, 1:3]
X1 X2 X3
2 b A e
3 c A e
7 c B e
11 c C e
12 d C e
16 d D e
17 a A f
18 b A f
20 d A f
22 b B f
24 d B f
25 a C f
27 c C f
28 d C f
29 a D f
31 c D f
HTH,
Dennis
On Sun, May 15, 2011 at 9:20 PM, Pierre Roudier
<pierre.roud...@gmail.com> wrote:
> Hi list,
>
> In a function I am writing, I need to extract the dimension names of
> an array. I know this can be acheived easily using dimnames() but my
> problem is that I want my function to be robust when the number of
> dimensions varies. Consider the following case:
>
> foo <- array(data = rnorm(32), dim = c(4,4,2),
> dimnames=list(letters[1:4], LETTERS[1:4], letters[5:6]))
>
> # What I want is to extract the *names of the dimensions* for which
> foo have positive values:
> ind <- which(foo > 0, arr.ind = TRUE)
>
> # A first solution is:
> t(apply(ind, 1, function(x) unlist(dimnames(foo[x[1], x[2], x[3],
> drop=FALSE]))))
> # But it does require to know the dimensions of foo
>
> I would like to do something like:
>
> ind <- which(foo > 0, arr.ind = TRUE)
> t(apply(ind, 1, function(x) unlist(dimnames(foo[x, drop=FALSE]))))
>
> but in that case the dimnames are dropped.
>
> Any suggestion?
>
> Cheers,
>
> Pierre
>
> --
> Scientist
> Landcare Research, New Zealand
>
> ______________________________________________
> 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.
>
______________________________________________
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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.
