programming-for-dummies

Chapter 3: Collections
and Dictionaries
In This Chapter
Storing data in a collection
Organizing data in a dictionary
Understanding hash tables and collisions
An array can be handy when you need to store the same type of information,
such as a group of integers. However, if you need to store different
information, such as both integers and strings, and you aren’t sure how
many items you need to store, you probably can’t use an array. Instead, you
can use a collection or a dictionary.
A collection acts like a resizable array that can hold different data types
at the same time while identifying each chunk of data with a number. A
dictionary acts like a collection that identifies each chunk of data with a
unique key.
The purpose of both collections and dictionaries is to make it easier to store
different types of data and retrieve them again with the size and single data
type restrictions of an array.
Using a Collection
A collection acts like a super array that can grow and expand without
requiring any special commands. In addition, a collection can store different
data types (such as integers or strings) or even other data structures, such
as an array.
Not all programming languages offer the collection data structure:
✦ In some programming languages (like Python and Smalltalk), collections
are a built-in feature of the language.
✦ In other languages (like C or Pascal), you have to use more primitive
data structures (like arrays) to mimic the features of a collection.
✦ In many newer languages (like C# and Visual Basic.NET), someone
else has already created a collection out of more primitive data structures,
so you can use them without knowing how they were created.