Re: Randomizing from a list of variables

[James C. W. <jfc...@ya...>]

--- On Wed, 6/29/11, Urs Holzer <ur...@an...> wrote:


From: Urs Holzer <ur...@an...>
Subject: Re: Randomizing from a list of variables
To: pip...@li...
Date: Wednesday, June 29, 2011, 2:42 AM


Hi James

James C. Wilson wrote:
> Thanks! I'm afraid I don't know what an array is, however...Could you
> explain if possible?

A value in Lua can be of type table. A table actually associates a key 
(which is also just a value) to another value. Of course it can have 
many entries. Say foo is a table, then

foo["bar"]

returns the value associated to the key "bar". Using

foo["bar"] = 1

Sets the value associated to the key "bar" to 1. In other words, a table 
stores values which you can read and set by key.

Lua does not know arrays as other programming languages do, since in 
Lua, an array is realized by a table which only has integers as keys. So 
if I say "array" here, I mean actually a table which has only integers 
as keys.

Example:

local sound = {}  -- create a table
sound[1] = sound1  -- sound now associates the value sound1 to the key 1
sound[2] = sound2  -- sound now associates the value sound2 to the key 2
sound[3] = sound3  -- sound now associates the value sound3 to the key 3

local n = 2  -- Store value 2 in the variable n
sound[n]  -- Returns the value associated to the key 2

You can read up more about tables here: http://www.lua.org/pil/2.5.html

Description from http://en.wikipedia.org/wiki/Associative_array:
An associative array (also associative container, map, mapping, 
dictionary, finite map, table, and in query-processing an index or index 
file) is an abstract data type composed of a collection of unique keys 
and a collection of values, where each key is associated with one value 
(or set of values). The operation of finding the value associated with a 
key is called a lookup or indexing, and this is the most important 
operation supported by an associative array. The relationship between a 
key and its value is sometimes called a mapping or binding. For example, 
if the value associated with the key "bob" is 7, we say that our array 
maps "bob" to 7. Associative arrays are very closely related to the 
mathematical concept of a function with a finite domain. As a 
consequence, a common and important use of associative arrays is in 
memoization.

Hope this helps

Greetings
Urs


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