[R] using IF command

[Dan Davison]

On Mon, Aug 11, 2008 at 08:23:19AM +1200, Gareth Campbell wrote:
> Hey team,
> 
> If I have a matrix:
> 
> 1, 2,
> 3, 4,
> 4, 0,
> 1, 3,
> 0, 3
> 
> 2 columns.
> 
> I want to write an if command that looks at (in this case) row 3 and looks
> to see if either [3,1] or [3,2] has a zero in it.  IF it does have a zero I
> want the zero to be placed in another matrix in the same position.  I know
> how to do the latter part, I just can't get the if command to look at both
> cells and deal with them separately.

I think you want to be using ifelse():

> a
     [,1] [,2]
[1,]    1    2
[2,]    3    4
[3,]    4    0
[4,]    1    3
[5,]    0    3
> b
     [,1] [,2]
[1,]    9    9
[2,]    9    9
[3,]    9    9
[4,]    9    9
[5,]    9    9
> ifelse(a == 0, a, b) ## do the whole thing
     [,1] [,2]
[1,]    9    9
[2,]    9    9
[3,]    9    0
[4,]    9    9
[5,]    0    9
> b[3,] <- ifelse(a[3,] == 0, a[3,], b[3,]) ## just row 3
> b
     [,1] [,2]
[1,]    9    9
[2,]    9    9
[3,]    9    0
[4,]    9    9
[5,]    9    9

Dan


> 
> Thanks
> 
> -- 
> Gareth Campbell
> PhD Candidate
> The University of Auckland
> 
> P +649 815 3670
> M +6421 256 3511
> E gareth.campbell at esr.cri.nz
> gcam032 at gmail.com
> 
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