structure returns the given object with further
an object which will have
various attributes attached to it.
attributes, specified in tag = value
form, which will be attached to data.
Adding a class "factor" will ensure that numeric codes are
given integer storage mode.
For historical reasons (these names are used when deparsing),
attributes ".Dim", ".Dimnames", ".Names",
".Tsp" and ".Label" are renamed to "dim",
"dimnames", "names", "tsp" and "levels".
It is possible to give the same tag more than once, in which case the
last value assigned wins. As with other ways of assigning attributes,
using tag = NULL removes attribute tag from .Data if
it is present.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
The New S Language.
Wadsworth & Brooks/Cole.