[R] matrix selection return types
vincent at 7d4.com
vincent at 7d4.com
Thu Jun 15 15:41:14 CEST 2006
Dear Rusers,
I would like some comments about the following results
(under R-2.2.0)
> m = matrix(1:6 , 2 , 3)
> m
[,1] [,2] [,3]
[1,] 1 3 5
[2,] 2 4 6
> z1 = m[(m[,1]==2),]
> z1
[1] 2 4 6
> is.matrix(z1)
[1] FALSE
> z2 = m[(m[,1]==0),]
> z2
[,1] [,2] [,3]
> is.matrix(z2)
[1] TRUE
Considered together, I'm a bit surprised about the
returned types from z1 and z2.
I would not have been surprised if z1 would still
have been a matrix, or z2=NULL.
There is certainly a logic behind this choice
but it's not very clear for me,
so any help/comment appreciated.
Thanks
Vincent
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