R help - Aug 2009 - Help with R Function writing for Matrix

Dear all,

I have a task to find the first all zero row of a matrix X ( nothing known
about X). I need to write a function which returns either the row index of
the first all-zero row, or NA if there are no all-zero rows. and I also need
to locate all rows which are non-zero (should be a vector of row indexes).

Can somebody give me some hints on this?

Thanks a lot.

Rene.

	[[alternative HTML version deleted]]

Try this:
> x <- matrix(1:40,ncol=5)
> # function to find zero rows
> f.zero <-
+ function(arr)
+ {
+     which(apply(arr, 1, function(z) all(z == 0)))[1]  # first one
+ }
>
> # now the non-zero rows
> f.nonzero <-
+ function(arr)
+ {
+     which(apply(arr, 1, function(z) any(z != 0)))
+ }
>
> f.zero(x)
[1] NA
> f.nonzero(x)
[1] 1 2 3 4 5 6 7 8
> # now make one zero
> x[3,] <- 0
> f.zero(x)
[1] 3
> f.nonzero(x)
[1] 1 2 4 5 6 7 8
> # more than one
> x[1,] <- 0
> f.zero(x)
[1] 1
> f.nonzero(x)
[1] 2 4 5 6 7 8
>

On Mon, Aug 10, 2009 at 6:15 AM, kaixin maleA<kaixinmalea at gmail.com>
wrote:
> Dear all,
>
> I have a task to find the first all zero row of a matrix X ( nothing known
> about X). I need to write a function which returns either the row index of
> the first all-zero row, or NA if there are no all-zero rows. and I also
need
> to locate all rows which are non-zero (should be a vector of row indexes).
>
> Can somebody give me some hints on this?
>
> Thanks a lot.
>
> Rene.
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?