[R] matrix indexing

[vito muggeo]

Dear tom,
is the following what you are looking for?

 > a=matrix(runif(9),3,3)
 > a
           [,1]      [,2]      [,3]
[1,] 0.9484247 0.9765431 0.6169739
[2,] 0.8423545 0.3137295 0.4031847
[3,] 0.6724235 0.1076373 0.2356923
 > b<-matrix(sample(c(TRUE,FALSE),size=9,replace=TRUE),3,3)
 > b
       [,1]  [,2]  [,3]
[1,] FALSE  TRUE  TRUE
[2,]  TRUE  TRUE  TRUE
[3,] FALSE FALSE FALSE
 > a[b]
[1] 0.8423545 0.9765431 0.3137295 0.6169739 0.4031847
 >

best,
vito

tom wright wrote:
> Can someone please give me a pointer here.
> I have two matrices
> 
> matA
> 	A	B	C
> 1	5	2	4
> 2	2	4	3
> 3	1	2	4
> 
> matB
> 	A	B	C
> 1	TRUE	FALSE	TRUE
> 2	FALSE	TRUE	TRUE
> 3	FALSE	FALSE	FALSE
> 
> how do I extract all the values from matA where the coresponding entry
> in matB == TRUE (or FALSE), perferably in vector form.
> 
> Many thanks
> tom
> 
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-- 
====================================
Vito M.R. Muggeo
Dip.to Sc Statist e Matem `Vianelli'
Università di Palermo
viale delle Scienze, edificio 13
90128 Palermo - ITALY
tel: 091 6626240
fax: 091 485726/485612