an efficient pairwise matrix cell's comparison function

A <- matrix(sample(0:2, 25, TRUE), ncol=5)
B <- matrix(1:25, ncol=5)
C <- ifelse(A == 0, 0, B)
A

B

C

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


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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]]

--
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?