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[R] Matrix multiplication using apply() or lappy() ?

toby marks

2006-09-06

Replies:

I am trying to divide the columns of a matrix by the first row in the
matrix.

I have tried to get this using apply and I seem to be missing a concept
regarding the apply w/o calling a function but rather command args %*% /
etc. Would using apply be more efficient than this approach?

I have observed examples in the archives using this type of approach. Does
anybody have a snippet of a call to apply() that would accomplish this as
well?

Thanks!


seed=50
$a = array(rnorm(20),dim=c(4,5))
$b = matrix(a[1,],dim(a)[1],dim(a)[2],byrow=T)
$a
      [,1]     [,2]     [,3]     [,4]     [,5]
[1,] -1.3682810 -0.4314462 1.57572752 0.67928882 -0.3672346
[2,] 0.4328180 0.6556479 0.64289931 0.08983289 0.1852306
[3,] -0.8113932 0.3219253 0.08976065 -2.99309008 0.5818237
[4,] 1.4441013 -0.7838389 0.27655075 0.28488295 1.3997368

$a/b
      [,1]     [,2]     [,3]     [,4]    [,5]
[1,] 1.0000000 1.0000000 1.00000000 1.0000000 1.000000
[2,] -0.3163225 -1.5196515 0.40800157 0.1322455 -0.504393
[3,] 0.5930018 -0.7461539 0.05696457 -4.4062113 -1.584338
[4,] -1.0554128 1.8167710 0.17550671 0.4193841 -3.811560



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