Array Concepts

Learning Goals

• Recognize array as a core programming tool
• Recognize array vocabulary word: Element
• Recognize array vocabulary word: Index
• Recognize array core property: Ordering
• View an Array in Ruby

Introduction

Much of life is understood by grouping things together based on a common characteristic. For instance, here are some groups you might have heard of:

• Family last name (The Simpsons)
• Band name (e.g. The Beatles)
• Grocery list

In most programming languages, the thing for storing a collection is called an "array". Arrays, as we'll learn, can also be used to order the things in the collection ("get the youngest Simpson" or "last grocery item").

Working with arrays is one of the most important tools to master in your programming career. In this lesson we'll make sure we know the vocabulary for working with arrays.

Recognize Array As a Core Programming Tool

The bulk of all programming work is taking inputs, doing some change to them (combining them, filtering them, attaching them together, etc.), and producing new output.

An array allows programmers

1. To create variables that store the input or output
2. To create variables that tell other programmers "there are a bunch of individuals data bits here, but, together, they make up something else, a collection, and knowing that fact is important."

Like all data structures, the Array has rules and we'll explore them in this lesson.

Example Data

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Let's establish an example for the rest of this lesson: the Shark Family as ordered by age, youngest to oldest. To keep things simple, we'll express this list in English, not in any programming language. In English, we tend to start numbering (or indexing) at 1, not 0, but the reverse is true in the programming world.

1. "Baby Shark"
2. "Mama Shark"
3. "Papa Shark"
4. "Grandma Shark"
5. "Grandpa Shark"

Recognize Array Vocabulary Word: Element

An individual member of an array is called an element. In our example, "Baby Shark" is an element. "Grandma Shark" is also an element. All arrays are collections of elements.

Recognize Array Vocabulary Word: Index

Earlier we mentioned that data structures have rules. The main rule of the array data structure is that the individual elements in an array can be "pointed to" by providing a number (Integer) and the name of the array.

In our example, we might say that in the lowest index (1) of the "Shark Family" array, we have "Baby Shark." In the highest index (6) of the "Shark Family" array, we have "Grandpa Shark."

Recognize Array Core Property: Ordering

Because arrays' elements are indexed by numbers that increase from a starting number by whole numbers, arrays can be used to keep elements in order.

Arrays can hold elements that aren't sorted (like "The Beatles" above), but programmers use the ordering property of the indexes to keep the collection in order. If the Shark family had a new baby shark we would put her in index 1 and move all the other sharks up one.

1. "Newborn Baby Sister Shark"
2. "Baby Shark"
3. "Mama Shark"
4. "Papa Shark"
5. "Grandma Shark"
6. "Grandpa Shark"

You'll have the chance to work with the ordering property hands-on shortly.

Let's look at our Shark family in the language of code.

View an Array in Ruby

In this example, imagine that the constant SHARK_FAMILY points to an Array and has already been defined for us (we'll learn to define Arrays in a moment).

In Ruby, we can print out an Array's contents with p and the name of the Array. If we had the following array entered into IRB:

2.3.3 :003 > SHARK_FAMILY = ["Baby Shark", "Mama Shark", "Papa Shark", "Grandma Shark", "Grandpa Shark"]
 => ["Baby Shark", "Mama Shark", "Papa Shark", "Grandma Shark", "Grandpa Shark"]

We could use p to print out SHARK_FAMILY:

2.3.3 :004 > p SHARK_FAMILY
["Baby Shark", "Mama Shark", "Papa Shark", "Grandma Shark", "Grandpa Shark"]
 => ["Baby Shark", "Mama Shark", "Papa Shark", "Grandma Shark", "Grandpa Shark"]

Ruby prints out the Array by putting square-brackets ([]) at the beginning and end of the Array. Between the brackets, it lists each of the elements, separated by commas (,). It does not show the indexes of each of the elements.

Looking at this output, we can see that there are 5 shark family members. At the lowest index, or "index 0" of SHARK_FAMILY, is "Baby Shark." At the largest index, or "index 4" of SHARK_FAMILY, is "Grandpa Shark."

Conclusion

In this lesson, we learned about the data structure Array. From iPhone to Java to Python, nearly every programming language has something like an Array. Arrays are composed of elements which are accessed by an index. Indexes move upward from 0 in Ruby and JavaScript. Arrays are often displayed in programming documentation in array literal syntax which is brackets ([]) filled with elements separated by ,s.

Resources

• Arrays
• Literals