# [R] inserting rows into a matrix

Gabor Grothendieck ggrothendieck at gmail.com
Thu Jul 27 16:36:45 CEST 2006

```Try this where f and A2 are as in your post:

out <-f(A2[A2>0])
replace(matrix(0, length(A2), ncol(out)), A2 > 0, out)

On 7/27/06, Robin Hankin <r.hankin at noc.soton.ac.uk> wrote:
> 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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