Key-based indexing can be used to simulate multi-dimensional arrays.

One example of a two-dimensional array is a table. Each item in the table has a row and a column. Shelf item keys can contain the row number and the column number separated by a separator character like period (.). Alternatively, if each row and column has a "name", then those names can be used in the keys instead of the row and column numbers. The following code is an example of a two-dimensional array, with the shelf item keys composed of the row number and column number for each item, separated by a period:

  down-translate
  
  global integer row
  global integer col
  global stream table variable
  
  element table
     clear table
     set row to 0
     suppress
  
  element row
     increment row
     set col to 0
     suppress
  
  element col
     increment col
     set table { "%d(row).%d(col)"} to "%c"

An example of a three-dimensional array with which most readers will be familiar is Rubik's Cube. Suppose we are using OmniMark to solve the cube. The cube is made up of 26 sub-cubes (the center, where you would expect to find the 27th, is empty and thus doesn't need to take up an item on our shelf). Each sub-cube is given a three-part key. The first part indicates where it is relative to the table: 1 if it's in the top layer, 2 if it's in the middle layer, and 3 if it's in the bottom layer. The second part of the key indicates if the sub-cube is in the left slice of the cube (1), the middle slice (2), or the right slice (3). Finally, the third part is used to tell if the sub-cube is facing us (1), in the middle (2), or facing away from us (3).

So, the top-left-front sub-cube would be indicated with a key of "1.1.1" and the bottom-right-rear sub-cube by "3.3.3". Note that there would be no item with a key of "2.2.2" because that is the empty position. An arbitrary position given by three integers, x, y, and z, can be specified by the key %d(x).%d(y).%d(z).

How this shelf would actually be used to solve Rubik's Cube is left as an exercise to the interested reader.

Using records

Another way to create multi-dimensional data structures it to use records. A record field is a shelf, and you can create a shelf of a record type, effectivly giving you shelves that can contain shelves. You can also use records to build other kinds of data structures such as trees.

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