Overview:
- Redis is an in-memory data structure.
- Redis supports several data structures. The set is one among them.
- It represents the mathematical concept of a set.
- The set supported by Redis is a set of strings.
- The Redis set supports several set operations like intersection, set subtraction, union of two sets.
- From a Python program redis-py module can be used to interface with a Redis server.
Adding elements to a Redis set:
- The Redis command SADD adds an element to a set.
- The Redis command SCARD returns the cardinality of the set. The cardinality of a set is the number of elements present in it.
- The Redis command SMEMBERS returns all the elements present in a set.
- This Python example uses the equivalent methods provided by redis-py for the Redis commands SADD, SCARD and SMEMBERS.
Example:
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# Sample Python program to demonstrate the set data structure supported by Redis
# import the python interface for Redis: The redis-py import redis
# Create a redis client redisClient = redis.StrictRedis(host='localhost', port=6379, db=0) # The name of the Redis set colorSet = "Colors"
# Add elements to the Redis set redisClient.sadd(colorSet, "Red") redisClient.sadd(colorSet, "Orange") redisClient.sadd(colorSet, "Yellow") redisClient.sadd(colorSet, "Green") redisClient.sadd(colorSet, "Blue") redisClient.sadd(colorSet, "Indigo") redisClient.sadd(colorSet, "violet")
# Print the cardinality of the Redis set print("Cardinality of the Redis set:") print(redisClient.scard(colorSet))
# Print all members of the Redis set print("Contents of the Redis set:") print(redisClient.smembers(colorSet)) |
Output:
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Cardinality of the Redis set: 7 Contents of the Redis set: {b'Indigo', b'violet', b'Orange', b'Yellow', b'Red', b'Green', b'Blue'} MyMac:dir1 usr1$ python3 set1.py Cardinality of the Redis set: 7 Contents of the Redis set: {b'Yellow', b'Green', b'Red', b'Blue', b'violet', b'Orange', b'Indigo'} |
Removing elements from a Redis set:
- The command SPOP removes an element from a Redis list and returns the value of the removed element.
- The SREM command removes an element with a specified value from the set.
Example:
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# Sample Python program to remove elements from a Redis set, using redis-py import redis
# Create a redis client redisClient = redis.StrictRedis(host='localhost', port=6379, db=0) # The name of the Redis set colors = "Hues"
# Add elements to the Redis set redisClient.sadd(colors, "Red") redisClient.sadd(colors, "Green") redisClient.sadd(colors, "Blue") redisClient.sadd(colors, "Yellow")
# Print the members of the Redis set before removing an element print("Initial contents of the Redis set:") print(redisClient.smembers(colors))
# Remove an element from a Redis set redisClient.srem(colors, "Yellow")
# Print the members of the Redis set after removing an element print("Contents of the Redis set after removing an element:") print(redisClient.smembers(colors))
# Remove the elements one by one while(redisClient.scard(colors) > 0): print("Removing {}...".format(redisClient.spop(colors)))
print("Length of the Redis set after removing all the elements:") print(redisClient.scard(colors)) |
Output:
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Initial contents of the Redis set: {b'Blue', b'Yellow', b'Green', b'Red'} Contents of the Redis set after removing an element: {b'Blue', b'Green', b'Red'} Removing b'Red'... Removing b'Blue'... Removing b'Green'... Length of the Redis set after removing all the elements: 0 |