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Weirdness with and without []: assignment of an object of class "numeric" is not valid for slot "values" in an object of class

Submitted by neale on
The following indicates that assignment of numeric values to an @values part of an mxMatrix only works when the [] are there. When they are not there (which used to work fine) we get an error:

> DirectionofCausationBcausesA$ACE.B@values
[,1] [,2]
[1,] 0 0
[2,] 0 0
> DirectionofCausationBcausesA$ACE.B@values[]
[,1] [,2]
[1,] 0 0
[2,] 0 0
>
> DirectionofCausationBcausesA$ACE.B@values<-0
Error in checkSlotAssignment(object, name, value) :
assignment of an object of class "numeric" is not valid for slot "values" in an object of class "FullMatrix"; is(value, "matrix") is not TRUE
>
>
> DirectionofCausationBcausesA$ACE.B@values
[,1] [,2]
[1,] 0 0
[2,] 0 0
>
> DirectionofCausationBcausesA$ACE.B@values[]<-0

Submitted by mspiegel on Wed, 03/24/2010 - 11:03

This is not a bug. The slots of a S4 object are typed objects. They are possibly the only objects in R that are typed objects. '0' is a numeric vector, while ACE.B@values expects a matrix type. Therefore the assignment ACE.B@values[] <- 0 is necessary.
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Submitted by mspiegel on Wed, 03/24/2010 - 11:06

An analogy would be:

foo <- matrix(1:9, 3, 3)
is.matrix(foo) # TRUE
foo <- 0
is.matrix(foo) # FALSE, oops
foo <- matrix(1:9, 3, 3)
foo[] <- 0
is.matrix(foo) # TRUE
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