Message-ID: <644e1f320803020418p4a0822e9ub1981723cc9ec8b6@mail.gmail.com>
Date: 2008-03-02T12:18:50Z
From: jim holtman
Subject: an efficient pairwise matrix cell's comparison function
In-Reply-To: <20080302120821.B9B1C1A0DD9@estafeta.csic.es>
Does this do what you want?
> A <- matrix(sample(0:2, 25, TRUE), ncol=5)
> B <- matrix(1:25, ncol=5)
> C <- ifelse(A == 0, 0, B)
> A
[,1] [,2] [,3] [,4] [,5]
[1,] 1 1 1 2 1
[2,] 1 0 1 1 0
[3,] 0 0 1 0 2
[4,] 0 1 2 0 0
[5,] 1 2 1 2 2
> B
[,1] [,2] [,3] [,4] [,5]
[1,] 1 6 11 16 21
[2,] 2 7 12 17 22
[3,] 3 8 13 18 23
[4,] 4 9 14 19 24
[5,] 5 10 15 20 25
> C
[,1] [,2] [,3] [,4] [,5]
[1,] 1 6 11 16 21
[2,] 2 0 12 17 0
[3,] 0 0 13 0 23
[4,] 0 9 14 0 0
[5,] 5 10 15 20 25
>
On Sun, Mar 2, 2008 at 7:11 AM, Diogo Andr? Alagador
<mcnda839 at mncn.csic.es> wrote:
> To all,
>
>
>
> I am undergoing an analysis involving big matrices of about 30000x200 which
> I have to handle in a more efficient way. So I would like some advice to
> build such efficient function to deliver the following result:
>
>
>
> - starting with 2 matrices of the same dimension (eg. A and B)
>
>
>
> 0 0 3 5 6 0 0 5
>
> A= 0 0 6 4 B= 0 4 3 5
>
> 0 0 5 0 1 0 0 9
>
>
>
> - the function should deliver a C matrix (same dimension too),
> where at each position C(i,j), compares A and B.
>
> if A(i,j)=0, than C(i,j)=0,
>
> if A(i,j)!=0, than C(i,j)=B(i,j)
>
>
>
> 6 0 0 5
>
> C= 0 0 3 5
>
> 0 0 0 0
>
>
>
> Although not an expert I could build a function with 2 cycles (reading
> columns and rows) which is not quick. Maybe you can help me in this
> "challenge".
>
>
>
> Much thanks in advance,
>
>
>
>
> Diogo Andr? Alagador
> Biodiversity & Global Change Lab, Museo Nacional de Ciencias Naturales,
> CSIC, Madrid, Espa?a
> Forest Research Centre, Instituto Superior de Agronomia, Universidade
> T?cnica de Lisboa, Lisboa, Portugal
>
>
> [[alternative HTML version deleted]]
>
>
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
>
--
Jim Holtman
Cincinnati, OH
+1 513 646 9390
What is the problem you are trying to solve?