Re: [R] inserting rows into a matrix

From: Christos Hatzis <christos_at_nuverabio.com>
Date: Fri 28 Jul 2006 - 00:10:21 EST


This is not as elegant, but should work:

a3 <- f(A2)
a3[ which( apply(a3,1,prod) == 0 ), ] <- rep(0,ncol(a3)) a3

Essentially use the product to pick out the rows with at least one 0 and replace these rows with 0s.

HTH.
-Christos

-----Original Message-----
From: r-help-bounces@stat.math.ethz.ch
[mailto:r-help-bounces@stat.math.ethz.ch] On Behalf Of Robin Hankin
Sent: Thursday, July 27, 2006 9:54 AM
To: RHelp
Subject: [R] inserting rows into a matrix

Hi

I have a little vector function that takes a vector A of strictly positive integers and outputs a matrix M each of whose columns is the vector, modified in a complicated combinatorical way.

Now I want to generalize the function so that A can include zeroes. Given A,
I want to strip out the zeroes, pass it to my function, and pad M   with rows at positions corresponding to the zeroes of A.

Commented, minimal, self-contained, reproducible toy example follows.

f <- function(a){cbind(a,a+1,rev(a))} #real function a ghastly nightmare

  A <- 1:5
  f(A)

      a
[1,] 1 2 5
[2,] 2 3 4

[3,] 3 4 3
[4,] 4 5 2
[5,] 5 6 1

# f() works as desired.

# Now introduce A2, that includes zeroes. In my application, f(A2) would fail because of the zeroes.

A2 <- c(1,0,0,2,4,0,3)

I can strip the zeroes out and call f():   f(A2[A2>0])

      a
[1,] 1 2 3
[2,] 2 3 4
[3,] 4 5 2
[4,] 3 4 1

which is fine. How to put the zeroes back in in the appropriate rows and get the following:

 > cbind(c(1,0,0,2,4,0,3),c(2,0,0,3,5,0,4),c(3,0,0,4,2,0,1))

      [,1] [,2] [,3]
[1,] 1 2 3
[2,] 0 0 0
[3,] 0 0 0
[4,] 2 3 4
[5,] 4 5 2
[6,] 0 0 0
[7,] 3 4 1
 >

anyone?

--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton European Way, Southampton SO14
3ZH, UK
  tel  023-8059-7743

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Received on Fri Jul 28 00:16:42 2006

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