[R] inserting rows into a matrix
Robin Hankin
r.hankin at noc.soton.ac.uk
Thu Jul 27 15:54:02 CEST 2006
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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