Chapter 11. Arrays
What Is an Array?
Back in Chapter 3, "Data and Datatypes", we learned that primitive datatypes -- strings, numbers, Booleans, null, and undefined -- represent basic information in our scripts. We also learned that ActionScript supports several composite datatypes, which can group several pieces of data together into a single datum.
The array type is the first composite datatype we'll study. Arrays are used to store and manipulate ordered lists of information and are, therefore, fundamental tools in sequential, repetitive programming. We use them to do everything from storing values retrieved via a user-input form, to generating pull-down menus, to keeping track of enemy spacecraft in a game. In its most basic form, an array is just a list of items, like your grocery list or the entries in your checkbook ledger.
11.1. What Is an Array?
An array is a data structure that can encompass multiple individual data values, just like a building is a physical structure encompassing multiple floors. Unlike a primitive datatype, an array can include more than one data value. Here is a simple example showing first, two strings, and then an array that contains two strings:
"oranges" // A single primitive string value "apples" // Another primitive string value ["oranges", "apples"] // A single array containing two strings
An array is a general-purpose container. It can contain any number of items and even items of different types. An array can even contain other arrays. Here is a simple example showing an array containing both strings and numbers. It might represent your shopping list and how many of each item you intend to buy:
["oranges", 6, "apples", 4, "bananas", 3]
Here's another analogy to make the concept of an array a little more tangible. Consider a chest of drawers. An individual drawer contains some content (socks, shirts, etc.). But the chest itself doesn't contain the content; it contains the drawers. The drawers hold the content. The chest organizes the drawers into a single unit.
When we work with an array (the chest of drawers), we are usually interested in the values within the array (the contents of the drawers). The values contained in an array are the information we want to manage. But we may also manipulate the containing structure itself. We may, for example, change an array's size (add or subtract drawers) or reorder its values (swap the contents of its drawers).
Though we speak of an array as containing many values, it's important to recognize that the array itself is a single datum the same way that a string containing multiple characters is still a single string and a number containing several digits is still a single number. As a single datum, an array may be assigned to a variable or used as part of a complex expression:
product = ["ladies downhill skis", 475] // Store an array in a variable display(product); // Pass that array to a function
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