Accessing elements (indexing, first, last) in Ruby - Step-by-Step Execution

Concept Flow - Accessing elements (indexing, first, last)

Start with Array

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Choose index or method

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Indexing: array[index

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Return element at index

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First element: array.first

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Return first element

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Last element: array.last

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Return last element

Start with an array, then access elements by index, or use .first or .last methods to get the first or last element.

Execution Sample

Ruby

arr = [10, 20, 30, 40]
puts arr[1]
puts arr.first
puts arr.last

This code prints the second element, then the first, then the last element of the array.

Execution Table

Step	Expression	Evaluation	Result	Output
1	arr = [10, 20, 30, 40]	Assign array to arr	[10, 20, 30, 40]
2	arr[1]	Access element at index 1	20	20
3	arr.first	Get first element	10	10
4	arr.last	Get last element	40	40
5	End	No more expressions

💡 All expressions evaluated, program ends.

Variable Tracker

Variable	Start	After Step 1	After Step 5
arr	undefined	[10, 20, 30, 40]	[10, 20, 30, 40]

Key Moments - 2 Insights

Why does arr[1] return 20 and not 10?

In Ruby, array indexing starts at 0, so arr[0] is 10, arr[1] is 20 as shown in step 2 of the execution_table.

What happens if I use arr.first on an empty array?

arr.first returns nil if the array is empty, because there is no first element. In Ruby, indexing out of range also returns nil.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output of arr[1] at step 2?

A 20

B 10

C 30

D 40

💡 Hint

Check the 'Result' and 'Output' columns in row for step 2.

At which step do we get the last element of the array?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look for the expression using arr.last in the execution_table.

If we change arr to [5, 15, 25], what would arr.first return?

A 15

B 5

C 25

D nil

💡 Hint

Refer to variable_tracker and remember arr.first returns the first element.

Concept Snapshot

Access elements in Ruby arrays using indexing or methods:
- array[index]: zero-based index access
- array.first: returns first element
- array.last: returns last element
Indexing out of range returns nil
.first and .last are safe for empty arrays

Full Transcript

This lesson shows how to get elements from a Ruby array. You can use array[index] where index starts at 0. For example, arr[1] gets the second element. You can also use arr.first to get the first element and arr.last to get the last element. These methods return nil if the array is empty, which is safe. The example code creates an array with four numbers and prints the second, first, and last elements. The execution table shows each step and the output. Remember, indexing starts at zero, so arr[0] is the first element. This helps you pick any element you want from an array easily.