Hi Antje

use the fact that n:1 counts backwards from n, and then use this as
a row index:

m <- matrix(1:30,5,6)
m[nrow(m):1,]
[,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

[
a more general answer would be

library(magic)
arev(m,1)
]

HTH

rksh

28 Jul 2006, at 08:50, <niederlein-rstat (AT) yahoo (DOT) dewrote:

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]]

R-help (AT) stat (DOT) math.ethz.ch mailing list

PLEASE do read the posting guide
guide.html
and provide commented, minimal, self-contained, reproducible code.

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?

28 Jul 2006, at 08:56, Jacques VESLT 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 VESLT

CNRS UMR 8090
I.B.L ( )
1 rue du Professeur Calmette
B.P. 245
59019 Lille Cedex

Tel : 33 (0)3.20.87.10.44
Fax : 33 (0)3.20.87.10.31

http://www-good.ibl.fr

--
niederlein-rstat (AT) yahoo (DOT) de a :
>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]]
>>
>
>R-help (AT) stat (DOT) math.ethz.ch mailing list
>
>PLEASE do read the posting guide
>guide.html
>and provide commented, minimal, self-contained, reproducible code.
>>
>

R-help (AT) stat (DOT) math.ethz.ch mailing list

PLEASE do read the posting guide
guide.html
and provide commented, minimal, self-contained, reproducible code.