Re: [R] Extracting the dimnames of an array with variable dimensions

From: <Bill.Venables_at_csiro.au>
Date: Mon, 16 May 2011 16:07:51 +1000

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-bounces_at_r-project.org [mailto:r-help-bounces_at_r-project.org] On Behalf Of Dennis Murphy Sent: Monday, 16 May 2011 3:14 PM
To: Pierre Roudier
Cc: r-help_at_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.roudier_at_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_at_r-project.org mailing list
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R-help_at_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.

R-help_at_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. Received on Mon 16 May 2011 - 06:18:35 GMT

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