Array slicing and ranges in Ruby - Step-by-Step Execution

Concept Flow - Array slicing and ranges

Start with array

↓

Define range or slice indices

↓

Extract elements using slice or range

↓

Return new array with selected elements

↓

Use or print sliced array

This flow shows how Ruby extracts parts of an array using slice indices or ranges, returning a new array with those elements.

Execution Sample

Ruby

arr = [10, 20, 30, 40, 50]
slice1 = arr[1..3]
slice2 = arr[2, 2]
puts slice1.inspect
puts slice2.inspect

This code slices the array using a range and using start index with length, then prints the results.

Execution Table

Step	Action	Expression	Result	Output
1	Define array	arr = [10, 20, 30, 40, 50]	[10, 20, 30, 40, 50]
2	Slice with range	slice1 = arr[1..3]	[20, 30, 40]
3	Slice with start and length	slice2 = arr[2, 2]	[30, 40]
4	Print slice1	puts slice1.inspect		[20, 30, 40]
5	Print slice2	puts slice2.inspect		[30, 40]
6	End	No more code

💡 All slices extracted and printed; program ends.

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
arr	[10, 20, 30, 40, 50]	[10, 20, 30, 40, 50]	[10, 20, 30, 40, 50]	[10, 20, 30, 40, 50]
slice1	nil	[20, 30, 40]	[20, 30, 40]	[20, 30, 40]
slice2	nil	nil	[30, 40]	[30, 40]

Key Moments - 2 Insights

Why does arr[1..3] include the element at index 3?

arr[1..3] uses a range which includes both start and end indices (1 to 3), so it includes index 3. arr[2, 2] uses start index 2 and length 2, so it includes indices 2 and 3 only, not index 4.

What happens if the range goes beyond the array length, like arr[3..10]?

Ruby returns elements from index 3 up to the end of the array without error, so it safely slices up to the array's last element.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of slice1 after step 2?

A [20, 30, 40]

B [30, 40]

C [10, 20, 30]

D nil

💡 Hint

Check the 'Result' column at step 2 in the execution_table.

At which step is slice2 assigned a value?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look for the assignment of slice2 in the 'Action' column.

If we change arr[2, 2] to arr[2..3], what would slice2 contain?

A [20, 30]

B [30, 40]

C [30, 40, 50]

D [40, 50]

💡 Hint

Compare how ranges and start,length slicing work in the variable_tracker.

Concept Snapshot

Array slicing in Ruby:
- arr[start..end] extracts elements from start to end index inclusive.
- arr[start, length] extracts length elements starting at start index.
- If range exceeds array length, slicing stops at array end.
- Returns a new array with selected elements.
- Useful for extracting parts of arrays easily.

Full Transcript

This visual trace shows how Ruby slices arrays using ranges and start-length pairs. We start with an array of five numbers. Using arr[1..3], Ruby extracts elements at indices 1, 2, and 3, returning [20, 30, 40]. Using arr[2, 2], Ruby extracts two elements starting at index 2, returning [30, 40]. The execution table tracks each step, showing variable values and outputs. Key moments clarify why ranges include the end index and how slicing beyond array length works safely. The quiz tests understanding of slice values and differences between slicing methods. The snapshot summarizes the syntax and behavior for quick reference.