Re: [R] mirror vector?

From: Robin Hankin <r.hankin_at_noc.soton.ac.uk>
Date: Fri 28 Jul 2006 - 18:05:07 EST

Hi

Not that there's anything wrong with Jacques's answer, but the List might be interested in the following gotcha:

 > m <- matrix(1:30,5,6)
 > apply(m,2,rev)

      [,1] [,2] [,3] [,4] [,5] [,6]

[1,]    5   10   15   20   25   30
[2,]    4    9   14   19   24   29
[3,]    3    8   13   18   23   28
[4,]    2    7   12   17   22   27
[5,]    1    6   11   16   21   26
 > apply(m,1,rev)
      [,1] [,2] [,3] [,4] [,5]
[1,]   26   27   28   29   30
[2,]   21   22   23   24   25
[3,]   16   17   18   19   20
[4,]   11   12   13   14   15

[5,] 6 7 8 9 10
[6,] 1 2 3 4 5
 >

See how the first usage of apply() works as expected (at least for me ;-)
but the second returns the transpose of what one might need. That's why I wrote arev().

comments anyone?

On 28 Jul 2006, at 08:56, Jacques VESLOT wrote:

>> mat <- matrix(1:16,4,4)
>> mat
> [,1] [,2] [,3] [,4]
> [1,] 1 5 9 13
> [2,] 2 6 10 14
> [3,] 3 7 11 15
> [4,] 4 8 12 16
>> apply(mat,2,rev)
> [,1] [,2] [,3] [,4]
> [1,] 4 8 12 16
> [2,] 3 7 11 15
> [3,] 2 6 10 14
> [4,] 1 5 9 13
>
> -------------------------------------------------------------------
> Jacques VESLOT
>
> CNRS UMR 8090
> I.B.L (2ème étage)
> 1 rue du Professeur Calmette
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>
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>
> http://www-good.ibl.fr
> -------------------------------------------------------------------
>
>
> niederlein-rstat@yahoo.de a écrit :
>> Hello,
>>
>> I'm an absolut beginner with R and now I got a 2D vector with
>> numbers. I would like to mirror this vector now by the rows (so
>> that the first row becomes last, second becomes one before
>> last, ...).
>> I don't know if there is any method I can use to do this.
>> Could you please help me?
>>
>> Antje
>>
>>
>> ---------------------------------
>> Was Sie schon immer wissen wollten aber nie zu Fragen trauten?
>> Yahoo! Clever hilft Ihnen.
>> [[alternative HTML version deleted]]
>>
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>>
>
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--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
  tel  023-8059-7743

______________________________________________
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Received on Fri Jul 28 19:31:31 2006

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