Running Me Ragged

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A
reader asked "Why
are there two types of multidimentional arrays? What is the difference between the (x)(y) and (x,y)
notation?"

Good
question. There are two kinds of multidimensional
arrays, called "rectangular" and "ragged". A
rectangular array is, well, rectangular. You
say

DIm
MyArrary(3,2)

and
you get an array with indices:

(0,0)
(0,1) (0,2)

(1,0)
(1,1) (1,2)

(2,0)
(2,1) (2,2)

(3,0)
(3,1) (3,2)

which
makes a nice rectangle. A three-dimensional
array makes a rectangular prism, and so on up into the higher dimensions.

Now,
as I mentioned earlier, JScript does not have multidimensional arrays. A
clever trick to simulate multidimensional arrays is to make an array of arrays:

var
x = new Array(

  new
Array(1, 2, 3),

  new
Array(4, 5),

  new
Array(6, 7, 8, 9));

And
so dereferencing the outer array gives you the inner array, which can then be dereferenced
itself:

print(x[2][0]);
// 6

But
you notice something about the indices if we write them out as before:

[0][0]
[0][1] [0][2]

[1][0]
[1][1]

[2][0]
[2][1] [2][2] [2][3]

The
indices make a ragged pattern, not a straight rectangular pattern.

You
can have ragged higher dimensional arrays as well, though allocating all the sub-arrays
gets to be a royal pain. 

There
are often times when you want ragged arrays even in a language that supports rectangular
multi-dimensional arrays, so VBScript supports both. If
you say

MyArray(2,3)

then
you are talking to a rectangular two-dimensional array. If
you say

MyArray(2)(3)

then
you are talking to a one dimensional array that contains another one dimensional array.