[R] logical comparison of two matrices

[Prof Brian Ripley]

Use all() or any() to reduce your comparison to a single logical value.
In your case all(S == P) appears to be what you intended, although maybe 
not what you wanted (see the next para).

Also check out ?identical and the comments in ?"==" (which BTW contains 
the answer to your question).

On 24 Jan 2004, Federico Calboli wrote:

> Dear All,
> 
> how can I get a logical comparison between matrices (or vectors) in a if
> statement?
> 
> Whenever I try I get the following:
> 
> 
> > S<-rbind(c(.25,0,0),c(0,.2,0),c(0,0,.1))
> > P<-rbind(c(.75,.15,.01),c(.2,.8,.09),c(.05,.05,.9))
> >
> >
> > aa<-function(S,P){
> + if (S == P){
> + return("OK")
> + }
> + else {
> + return("No match")
> + }
> + }
> >
> >
> > aa(S,P)
> [1] "No match"
> Warning message:
> the condition has length > 1 and only the first element will be used in:
> if (S == P) {
> 
> The warning clearly states that only the first element was used, and
> this would not be good enough.
> 
> If comparing the whole matrices is not possible I could be happy just
> comparing the two diagonals.
> 
> regards,
> 
> Federico Calboli
> 
> 
> 
> 

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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