[R] mirror vector?

[Robin Hankin]

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
>
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> http://www-good.ibl.fr
> -------------------------------------------------------------------
>
>
> niederlein-rstat at 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.
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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