replace() in matrix

How do I replace values of a matrix, for exemple I want the matrix

1	24	1	1	1
24	1	1	1	1
1	1	1	45	104
1	1	45	1	92
1	1	104	92	1

to be replaced by 

0	24	0	0	0
24	0	0	0	0
0	0	0	45	104
0	0	45	0	92
0	0	104	92	0

Could someone please help me with that?

It is explained in the "An introduction to R" manual (which is included
in the main R distribution) under
"Index vectors: selecting and modifying subsets of a data set"

An example is

a <- matrix(c(1,24,1,103,56,1,1,1,27),3,3)
a

[,1] [,2] [,3]
[1,]    1  103    1
[2,]   24   56    1
[3,]    1    1   27

a[a<=1] <- 0 
a

[,1] [,2] [,3]
[1,]    0  103    0
[2,]   24   56    0
[3,]    0    0   27

guido




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