Array sorting and reversing in Ruby - Step-by-Step Execution

Concept Flow - Array sorting and reversing

Start with array

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Call sort method

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Compare elements

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Rearrange elements in ascending order

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Sorted array ready

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Call reverse method

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Swap elements from ends towards center

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Reversed array ready

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End

The array is first sorted by comparing and rearranging elements in ascending order, then reversed by swapping elements from the ends towards the center.

Execution Sample

Ruby

arr = [3, 1, 4, 2]
sorted_arr = arr.sort
reversed_arr = sorted_arr.reverse
puts reversed_arr

This code sorts the array in ascending order, then reverses it, and prints the reversed array.

Execution Table

Step	Action	Array State	Output/Result
1	Initialize arr	[3, 1, 4, 2]	None
2	Call arr.sort	[3, 1, 4, 2]	Returns [1, 2, 3, 4]
3	Assign sorted_arr	[1, 2, 3, 4]	None
4	Call sorted_arr.reverse	[1, 2, 3, 4]	Returns [4, 3, 2, 1]
5	Assign reversed_arr	[4, 3, 2, 1]	None
6	Print reversed_arr	[4, 3, 2, 1]	4 3 2 1
7	End	[4, 3, 2, 1]	Program ends

💡 All steps completed, program ends after printing reversed array.

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
arr	[3, 1, 4, 2]	[3, 1, 4, 2]	[3, 1, 4, 2]	[3, 1, 4, 2]
sorted_arr	nil	nil	[1, 2, 3, 4]	[1, 2, 3, 4]
reversed_arr	nil	nil	nil	[4, 3, 2, 1]

Key Moments - 3 Insights

Why does arr.sort not change the original array 'arr'?

Because in Ruby, 'sort' returns a new sorted array and does not modify the original array. This is shown in execution_table step 2 where 'arr' stays the same but 'sorted_arr' gets the sorted values.

What does reverse do to the array?

The 'reverse' method returns a new array with elements in opposite order. In step 4, 'sorted_arr' remains ascending, but 'reversed_arr' gets the reversed order.

Why do we assign the result of sort and reverse to new variables?

Because both 'sort' and 'reverse' return new arrays without changing the original. Assigning to new variables keeps the results accessible, as seen in steps 3 and 5.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'sorted_arr' after step 2?

A nil

B [3, 1, 4, 2]

C [1, 2, 3, 4]

D [4, 3, 2, 1]

💡 Hint

Check variable_tracker for 'sorted_arr' after step 2; it is assigned after step 3.

At which step does the array become reversed?

A Step 2

B Step 4

C Step 3

D Step 6

💡 Hint

Look at execution_table step 4 where reverse is called and reversed_arr is assigned.

If we changed 'arr.sort' to 'arr.sort!' (with exclamation), how would 'arr' change after step 2?

A It would remain [3, 1, 4, 2]

B It would become [4, 3, 2, 1]

C It would become [1, 2, 3, 4]

D It would become nil

💡 Hint

In Ruby, methods ending with '!' modify the original object, so 'arr' would be sorted in place.

Concept Snapshot

Array sorting and reversing in Ruby:
- Use arr.sort to get a new sorted array (original unchanged).
- Use arr.sort! to sort in place (modifies original).
- Use arr.reverse to get a new reversed array.
- Use arr.reverse! to reverse in place.
- Assign results to variables to keep changes.

Full Transcript

This visual trace shows how Ruby arrays can be sorted and reversed. Starting with an array [3, 1, 4, 2], calling 'sort' returns a new sorted array [1, 2, 3, 4] without changing the original. Then calling 'reverse' on the sorted array returns a new reversed array [4, 3, 2, 1]. Variables track these changes step by step. Key points include understanding that 'sort' and 'reverse' return new arrays, so assigning their results is necessary to keep changes. The quiz tests understanding of when variables change and the difference between methods that modify in place and those that don't.