Concatenate any number of pairs of x and y
Any number of arguments, each of which is a structure
containing elements x and y.
A list with two components x and y, which are the
concatenations of all the corresponding x and y
vectors in the argument list.
This function can be used to superimpose two or more point patterns
of unmarked points (but see also superimpose which is
It assumes that each of the arguments in
... is a structure containing (at least) the elements
x and y. It concatenates all the x elements
into a vector x, and similarly for y, and returns these