[R] {Spam?} Re: sort a 3 dimensional array across third dimension ?

[Claudia Beleites]

On 02/18/2011 04:11 PM, Maas James Dr (MED) wrote:
> Hi Claudia,
>
> It does help a lot, but not quite there yet ... I'm sure you are correct and
> is much appreciated, I need some sort of generalized form, actual arrays in
> my case are 3x3x1000.  Do you suspect it could be done in one step with
> sapply?
Why sapply?

Sure you can to it in one step:
y<- aperm (apply (x, 1:2, sort), c(2, 3, 1))
I just think two lines are more readable.

Note that all these numbers are the "directions" of the array and don't have 
anything to do with the actual size. Just try it out with different array sizes.

 > a <- array (runif (9000), c (3, 3, 1000))
 > a [,,1:2]
, , 1

        [,1]   [,2]    [,3]
[1,] 0.8721 0.5102 0.47370
[2,] 0.7721 0.5744 0.98281
[3,] 0.9357 0.1969 0.08784

, , 2

        [,1]   [,2]   [,3]
[1,] 0.1485 0.6878 0.1018
[2,] 0.3784 0.3864 0.9814
[3,] 0.9219 0.5664 0.4565

 > y<- aperm (apply (a, 1:2, sort), c(2, 3, 1))
 > y [,,1:2]
, , 1

           [,1]      [,2]      [,3]
[1,] 1.121e-03 1.517e-03 0.0008285
[2,] 7.118e-05 3.303e-04 0.0003870
[3,] 7.445e-04 2.461e-05 0.0005980

, , 2

          [,1]      [,2]     [,3]
[1,] 0.001375 0.0049272 0.004581
[2,] 0.002204 0.0004947 0.001148
[3,] 0.004214 0.0006355 0.001610

 > y [,,999:1000]
, , 1

        [,1]   [,2]   [,3]
[1,] 0.9989 0.9980 0.9998
[2,] 0.9982 0.9973 0.9994
[3,] 0.9994 0.9978 0.9993

, , 2

        [,1]   [,2]   [,3]
[1,] 0.9997 0.9992 0.9999
[2,] 0.9986 0.9981 0.9997
[3,] 0.9998 0.9988 0.9996


BTW: as your MARGINS are short, only 3 x 3 = 9 calls to FUN are necessary. I 
don't think you can gain much time here. The calculation with 3 x 3 x 1000 on my 
computer had 3 ms elapsed, and increasing every direction by a factor of 10 
still needs 1/3 s.



Claudia



>
> Regards
>
> J
>
>
> =============================== Dr. Jim Maas Research Associate in Network
> Meta-Analysis School of Medicine, Health Policy and Practice CD Annex, Room
> 1.04 University of East Anglia Norwich, UK NR4 7TJ
>
> +44 (0) 1603 591412
>
>
>> From: Claudia Beleites [mailto:cbeleites at units.it]
>>
>> Dear James,
>>
>> this is what I understood your sorting along the third dimension to be:
>>> x<- array(c(9, 9, 7, 9, 6, 5, 4, 6, 2, 1, 3, 2), dim = list(2, 2,
>> 3))
>>
>>> y<- apply (x, 1:2, sort) y
>> , , 1
>>
>> [,1] [,2] [1,]    2    1 [2,]    6    5 [3,]    9    9
>>
>> , , 2
>>
>> [,1] [,2] [1,]    3    2 [2,]    4    6 [3,]    7    9
>>
>>
>> The results of apply are length (result of function) x [shape of x without
>> the dimensions you hand to apply).
>>
>> Thus, your specified result needs rearranging the dimensions:
>>
>>> y<- aperm (y, c(2, 3, 1)) y
>> , , 1
>>
>> [,1] [,2] [1,]    2    3 [2,]    1    2
>>
>> , , 2
>>
>> [,1] [,2] [1,]    6    4 [2,]    5    6
>>
>> , , 3
>>
>> [,1] [,2] [1,]    9    7 [2,]    9    9
>>
>>
>> HTH Claudia
>>
>> -- Claudia Beleites Dipartimento dei Materiali e delle Risorse Naturali
>> Università degli Studi di Trieste Via Alfonso Valerio 6/a I-34127 Trieste
>>
>> phone: +39 0 40 5 58-37 68 email: cbeleites at units.it


-- 
Claudia Beleites
Dipartimento dei Materiali e delle Risorse Naturali
Università degli Studi di Trieste
Via Alfonso Valerio 6/a
I-34127 Trieste

phone: +39 0 40 5 58-37 68
email: cbeleites at units.it