Sort_by for custom sorting in Ruby - Step-by-Step Execution

Concept Flow - Sort_by for custom sorting

Start with array

↓

Apply sort_by block

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Transform each element to sort key

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Sort elements by keys

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Return sorted array

The array is transformed by a block to keys used for sorting, then sorted by those keys, returning a new sorted array.

Execution Sample

Ruby

words = ["apple", "pear", "banana"]
sorted = words.sort_by { |word| word.length }
puts sorted

Sorts the array of words by their length in ascending order.

Execution Table

Step	Element	Sort Key (word.length)	Action	Resulting Array State
1	"apple"	5	Calculate key	["apple", "pear", "banana"]
2	"pear"	4	Calculate key	["apple", "pear", "banana"]
3	"banana"	6	Calculate key	["apple", "pear", "banana"]
4	All keys calculated	-	Sort by keys	["pear", "apple", "banana"]
5	Return sorted array	-	Output sorted array	["pear", "apple", "banana"]

💡 All elements transformed to keys and sorted by those keys, sorting ends.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
words	["apple", "pear", "banana"]	["apple", "pear", "banana"]	["apple", "pear", "banana"]	["apple", "pear", "banana"]	["apple", "pear", "banana"]
sorted	nil	nil	nil	nil	["pear", "apple", "banana"]

Key Moments - 2 Insights

Why does sort_by use the block's return value instead of the element itself to sort?

sort_by transforms each element into a key using the block (see steps 1-3 in execution_table). It sorts by these keys, not the original elements, allowing custom sorting criteria.

Does sort_by change the original array?

No, as shown in variable_tracker, the original array 'words' stays the same. sort_by returns a new sorted array stored in 'sorted' (step 5).

Visual Quiz - 3 Questions

Look at the execution_table at step 2, what is the sort key for "pear"?

A 5

B 4

C 6

D 3

💡 Hint

Check the 'Sort Key (word.length)' column at step 2 in execution_table.

At which step does the array get sorted by the keys?

A Step 4

B Step 2

C Step 3

D Step 5

💡 Hint

Look for the 'Action' column mentioning sorting in execution_table.

If we changed the block to sort by the last letter of each word, how would the sort keys change?

A Keys would be word lengths

B Keys would be the first character of each word

C Keys would be the last character of each word

D Keys would be the whole word

💡 Hint

sort_by uses the block return value as key; changing block changes keys (see concept_flow).

Concept Snapshot

sort_by { |element| key } transforms each element to a key
Sorts elements by these keys ascending
Returns new sorted array, original unchanged
Useful for custom sorting criteria
Example: array.sort_by { |x| x.length }

Full Transcript

This example shows how Ruby's sort_by method works. We start with an array of words. Each word is passed to the block, which returns the word's length as the sort key. The method collects these keys, then sorts the original elements by these keys. The original array remains unchanged. The result is a new array sorted by word length. This process is shown step-by-step in the execution table and variable tracker. Key moments clarify why sort_by uses keys and does not modify the original array. The quiz tests understanding of keys and sorting steps.