On Thu, 25 Dec 2014, Duncan Murdoch wrote:
On 25/12/2014 1:57 PM, Mike Miller wrote:
I do think I get what is going on with this, but why should I buy into
this conceptualization? Why is it better to say that a matrix *is* a
vector than to say that a matrix *contains* a vector? The latter seems
to be the more common way of thinking but such things.
"More common"? The better way to think of this is as a class hierarchy.
A matrix is a particular kind of vector (the kind that has a dimension
attribute). A matrix has all the properties that a vector has, plus
some more.
Would you say a cube contains a polygon, or a cube is a polygon?
I would say that the sides of the cube are polygons, so I guess a cube
"contains" six polygons, but "is" would be wrong because a cube is a
polyhedron, not a polygon. A cube is not a polygon.
I get your point about hierarchy.
Someone else showed me that setting the dim attribute to NULL changes the
matrix into a vector so that is.vector() is TRUE.
Mike
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