List vs sorted set for sequences in Redis - Visual Side-by-Side Comparison

Concept Flow - List vs sorted set for sequences

Start

↓

Choose data structure

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List

↓

Add elements at ends

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Retrieve by index

↓

Order is insertion order

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Sorted Set

↓

Add elements with scores

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Retrieve by score or rank

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Order by score

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Unique elements only

You start by choosing either a List or a Sorted Set to store sequences. Lists keep order by insertion and allow duplicates. Sorted Sets store unique elements with scores that define order.

Execution Sample

Redis

LPUSH mylist A
LPUSH mylist B
ZADD myzset 1 A
ZADD myzset 2 B
ZRANGE myzset 0 -1 WITHSCORES

This shows adding elements to a Redis List and a Sorted Set, then retrieving them.

Execution Table

Step	Command	Action	Data Structure State	Output
1	LPUSH mylist A	Add 'A' to head of list	List: ['A']	1 (new length)
2	LPUSH mylist B	Add 'B' to head of list	List: ['B', 'A']	2 (new length)
3	ZADD myzset 1 A	Add 'A' with score 1	Sorted Set: {'A':1}	1 (added)
4	ZADD myzset 2 B	Add 'B' with score 2	Sorted Set: {'A':1, 'B':2}	1 (added)
5	ZRANGE myzset 0 -1 WITHSCORES	Retrieve all elements by score ascending	Sorted Set unchanged	['A', '1', 'B', '2']
6	LRANGE mylist 0 -1	Retrieve all elements by index	List unchanged	['B', 'A']
7	LPUSH mylist A	Add duplicate 'A' to head	List: ['A', 'B', 'A']	3 (new length)
8	ZADD myzset 3 A	Update score of 'A' to 3	Sorted Set: {'A':3, 'B':2}	0 (updated)
9	ZRANGE myzset 0 -1 WITHSCORES	Retrieve all elements by score ascending	Sorted Set unchanged	['B', '2', 'A', '3']
10	LRANGE mylist 0 -1	Retrieve all elements by index	List unchanged	['A', 'B', 'A']
11	End	No more commands	Final states	See above

💡 Commands complete; final states show List allows duplicates and order by insertion; Sorted Set orders by score and keeps unique elements.

Variable Tracker

Data Structure	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 7	After Step 8	Final
List 'mylist'	[]	['A']	['B', 'A']	['B', 'A']	['B', 'A']	['A', 'B', 'A']	['A', 'B', 'A']	['A', 'B', 'A']
Sorted Set 'myzset'	{}	{}	{}	{'A':1}	{'A':1, 'B':2}	{'A':1, 'B':2}	{'A':3, 'B':2}	{'A':3, 'B':2}

Key Moments - 2 Insights

Why does the List allow duplicate elements but the Sorted Set does not?

The execution_table rows 7 and 8 show that adding 'A' again to the List adds a new element (step 7), but adding 'A' to the Sorted Set updates its score instead of adding a duplicate (step 8). Sorted Sets enforce uniqueness by element.

How is the order of elements determined differently in List and Sorted Set?

Rows 2 and 4 show List order is by insertion at head (new elements appear first), while Sorted Set order is by score ascending (rows 5 and 9). This means List keeps insertion order, Sorted Set sorts by score.

Visual Quiz - 3 Questions

Look at the execution_table at step 7. What is the state of the List 'mylist'?

A ['A', 'B', 'A']

B ['B', 'A']

C ['A', 'A', 'B']

D ['B', 'A', 'B']

💡 Hint

Check the 'Data Structure State' column at step 7 in execution_table.

At which step does the Sorted Set update the score of an existing element?

A Step 4

B Step 8

C Step 3

D Step 7

💡 Hint

Look for 'Update score' action in the execution_table.

If you retrieve all elements from the Sorted Set after step 9, what order will they be in?

A ['A', 'B']

B ['A', 'A', 'B']

C ['B', 'A']

D ['B', 'A', 'B']

💡 Hint

Check the output of ZRANGE at step 9 in execution_table.

Concept Snapshot

Redis List stores sequences allowing duplicates and keeps insertion order.
Use LPUSH or RPUSH to add elements.
Retrieve by index with LRANGE.
Sorted Set stores unique elements with scores.
Use ZADD to add/update with score.
Retrieve ordered by score with ZRANGE.
Lists allow duplicates; Sorted Sets do not.
Lists order by insertion; Sorted Sets order by score.

Full Transcript

This visual execution compares Redis List and Sorted Set for sequences. Lists add elements at the head or tail and keep duplicates and insertion order. Sorted Sets add unique elements with scores that define order. The execution table shows commands adding elements, retrieving them, and updating scores. Lists allow duplicates as seen when 'A' is added twice. Sorted Sets update scores instead of duplicates. Retrieval from Lists returns elements in insertion order; Sorted Sets return elements ordered by score. This helps choose the right structure for your sequence needs.