The Ruby Way: Solutions and Techniques in Ruby Programming, Second Edition

8.2. Working with Hashes

Hashes are known in some circles as associative arrays, dictionaries, and various other names. Perl and Java programmers in particular will be familiar with this data structure.

Think of an array as an entity that creates an association between an index x and a data item y. A hash creates a similar association with at least two exceptions. First, for an array, x is always an integer; for a hash, it need not be. Second, an array is an ordered data structure; a hash typically has no ordering.

A hash key can be of any arbitrary type. As a side effect, this makes a hash a nonsequential data structure. In an array, we know that element 4 follows element 3; but in a hash, the key may be of a type that does not define a real ...