Other Data Structures

Although web apps are ultimately about strings, actually making those strings requires using other data structures as well. In this section, we’ll learn about some Ruby data structures important for writing Rails applications.

Arrays and Ranges

An array is just a list of elements in a particular order. We haven’t discussed arrays yet in the Rails Tutorial, but understanding them gives a good foundation for understanding hashes (Section 4.3.3) and for aspects of Rails data modeling (such as the has_many association seen in Section 2.3.3 and covered more in Section 10.1.3).

         So far we’ve spent a lot of time understanding strings, and there’s a natural way to get from strings to arrays using the split method:

The result of this operation is an array of three strings. By default, split divides a string into an array by splitting on whitespace, but you can split on nearly anything else as well:  

As is conventional in most computer languages, Ruby arrays are zero-offset, which  means that the first element in the array has index 0, the second has index 1, and so on: 

We see here that Ruby uses square brackets to access array elements. In addition to this bracket notation, Ruby offers synonyms for some commonly accessed elements:6

This last line introduces the equality comparison operator ==, which Ruby shares with many other languages, along with the associated != (‘‘not equal’’), etc.: 

 In addition to length (seen in the first line above), arrays respond to a wealth of other methods: