Sets

Redis Sets

A Redis set is an unordered collection of unique strings. Duplicate members are automatically ignored. Sets are ideal for tracking unique items, managing relationships, and performing set operations.

SADD — Add Members

SADD online "Alice" "Bob" "Charlie"
SADD online "Alice"    -- duplicate, ignored
SCARD online            -- count = 3

Output:

(integer) 3
(integer) 0
(integer) 3

SMEMBERS — Get All Members

Returns all members in sorted order (alphabetically in this emulator):

SMEMBERS online

Output:

1) "Alice"
2) "Bob"
3) "Charlie"

SISMEMBER — Check Membership

SISMEMBER online "Alice"    -- 1 (true)
SISMEMBER online "Dave"     -- 0 (false)

SCARD — Set Cardinality (Size)

SCARD online

SREM — Remove Members

SREM online "Charlie"
SCARD online    -- now 2

Set Operations — SUNION, SINTER, SDIFF

These are some of Redis's most powerful features:

SADD team_a "Alice" "Bob" "Charlie"
SADD team_b "Bob" "Charlie" "Dave"

SUNION team_a team_b      -- all unique members across both sets
SINTER team_a team_b      -- members in BOTH sets
SDIFF team_a team_b       -- members in team_a but NOT team_b

Output:

1) "Alice"
2) "Bob"
3) "Charlie"
4) "Dave"
---
1) "Bob"
2) "Charlie"
---
1) "Alice"

Real-World Patterns

Who follows both Alice and Bob?

SADD followers:alice "u1" "u2" "u3"
SADD followers:bob "u2" "u3" "u4"
SINTER followers:alice followers:bob    -- u2, u3

Unique visitors today:

SADD visitors:2024-01-15 "user1" "user2" "user1"
SCARD visitors:2024-01-15    -- 2 unique

Your Task

Create two sets: python_devs with members "Alice", "Bob", "Charlie" and "js_devs" with members "Bob", "Charlie", "Dave". Use SINTER to find developers who know both languages.