Hi
On 2 Jun 2006 at 10:26, Uwe Ligges wrote:
Date sent: Fri, 02 Jun 2006 10:26:44 +0200
From: Uwe Ligges <ligges at statistik.uni-dortmund.de>
Organization: Fachbereich Statistik, Universitaet Dortmund
To: Tim Alcon <talcon at iastate.edu>
Copies to: r-help at stat.math.ethz.ch
Subject: Re: [R] basic array question
> Tim Alcon wrote:
> > I have a large array and would like to extract from it the row and
> > column indices just of values for which a particular boolean
> > condition
>
> Do you mean a matrix, i.e. exactly 2 dimensions?
>
> > is true. I assume there's a simple way to do this, but I
haven't
> > figured it out yet. Any help would be appreciated.
>
> Example:
>
>
> X <- matrix(1:9, 3)
> col(X)[X == 4]
> row(X)[X == 4]
>
or
> which(X==4, arr.ind=T)
row col
[1,] 1 2>
which works on higher dim arrays too
> X <- array(1:12, c(3,2,2))
> X
, , 1
[,1] [,2]
[1,] 1 4
[2,] 2 5
[3,] 3 6
, , 2
[,1] [,2]
[1,] 7 10
[2,] 8 11
[3,] 9 12
> which(X==6, arr.ind=T)
dim1 dim2 dim3
[1,] 3 2 1>
HTH
Petr
> Uwe Ligges
>
> > Tim
> >
> > ______________________________________________
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>
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Petr Pikal
petr.pikal at precheza.cz