Set is a
direct subtype of Data with functions Set Functions, keys Set keys and example object Set#2 that represents a set of N arrays that are presented in the form of a table.
For i = 1, ..., N, the iᵗʰ array consists of the u values xⁱ₁, xⁱ₂, ..., xⁱᵤ that can be of any type.

The N arrays may be stacked vertically (vertical table orientation) or horizontally (horizontal table orientation).
In the vertical case, there exist N rows with each row containing u component cells.
In the horizontal case, there exist N columns with each column containing u component cells.

Most common is the vertical orientation because for very large N the visual display of N arrays arranged over a range consisting of N rows is preferable to its transposed orientation where the N arrays are arranged over a range consisting of N columns.

The u array components may be optionally identified by u
titles, which - if they exist - must appear at the topmost row (vertical case) or leftmost column (horizontal case).