Arrays in LC [was: Re: [TAO] value() to obtain pointer functionality]

[Richard Gaskin]

Peter Haworth wrote:

 > I may be misunderstanding but does that imply it's still possible to
 > create "old style" arrays in Livecode?  As a relative newcomer to LC,
 > I've only ever known about the current form of arrays and wouldn't
 > know how to set about creating one of the original arrays.

An array is just a collection of key-value pairs, and with associative 
arrays each key is a string.

All that's changed in recent years is that -- in addition to any text or 
binary data as we've always had -- you can now use an array as the value 
for an element, effectively nesting them.

But for keys at any level, a string is a string, whether it's:

    get tArray["Bob"]

...or:

    get tArray["1"]

...or:

    get tArray[1]

...or:

    get tArray["1,2"]

...or:

    put 1 into tFirstPart
    put 2 into tSecondPart
    get tArray[ tFirstPart, tSecondPart]

If you need to work on an array that's stored as the value in another 
array, you'll want to use:

    put tArray[1] into tAnotherArray
    get tAnotherArray[2]

...or shorter, you can access the second-level array without extracting 
it first by using a second set of brackets:

    get tArray[1][2]

But with many uses, such as matrix multiplication, you'll probably never 
need to be able to treat the second dimension as an extractable subset, 
more interested in the collection as a whole.

So when working on one collection you can use:

   get tArray[1,2]

We could illustrate each like this:

   One-dimensional
   tArray keys:
      1,1
      1,2
      1,3
      2,1
      2,2
      2,3


   Two-dimensional
   tArray keys:
      1
        tArray[1] keys:
          1
          2
          3
      2
        tArray[2] keys:
          1
          2
          3


Multidimensional arrays are very useful when the second (and any 
subsequent dimensions) may be needed to be worked on as collections in 
themselves.

But when only working on one collection as a whole, it probably doesn't 
matter much whether you organize your collection as a one-dimensional 
array in which parts of the key string provide a sort of row-and-column 
designation, or make a two-dimensional array.

One advantage of the former is that it allows you to use the existing 
matrixMultiply. :)

There may also be a modest performance gain from using a 
single-dimensional array when practical, because each dimension has to 
run the key through a hash function to determine the memory location of 
its associated value.  That said, the hashes used for most associative 
aren't nearly as complex as cryptographic hashes, so I doubt the 
performance difference would matter much.

-- 
  Richard Gaskin
  Fourth World Systems
  Software Design and Development for the Desktop, Mobile, and the Web
  ____________________________________________________________________
  Ambassador at FourthWorld.com                http://www.FourthWorld.com