Set operations

Rediset's main purpose is to perform operations on sets, and then compose the results. The operations that Rediset provides are Union, Intersection and Difference. See the Redis documentation for full details on the semantics of these operations.

>>> rs = Rediset()
>>>
>>> nirvana = rs.Set('nirvana')
>>> nirvana.add('kurt', 'krist', 'dave')
>>>
>>> foo_fighters = rs.Set('foo_fighters')
>>> foo_fighters.add('dave', 'nate', 'taylor', 'chris', 'pat')
>>>
>>> nirvana_and_ff = rs.Intersection(nirvana, foo_fighters)
>>> set(nirvana_and_ff)
set(['dave'])

Simple so far. But what if we wanted to know everyone who has been in either Nirvana and the Foo Fighters, or Blur and Gorillaz? We need to create a Union of the two Intersections:

>>> blur = rs.Set('blur')
>>> blur.add('damon', 'graham', 'alex', 'dave')
>>>
>>> gorillaz = rs.Set('gorillaz')
>>> gorillaz.add('damon', 'jamie')
>>>
>>> result = rs.Union(
...     rs.Intersection(nirvana, foo_fighters),
...     rs.Intersection(blur, gorillaz)
... )
>>> set(result)
set(['dave', 'damon'])

You can nest these operations as deeply as you like (see below for details).

Notes on operations

You can't mutate an operation (Union, Intersection or Difference) directly:

>>> u = rs.Union(rs.Set('key1'), rs.Set('bar'))
>>> u.add('a')
Traceback (most recent call last):
  File "<input>", line 1, in <module>
AttributeError: 'UnionNode' object has no attribute 'add'

As a shortcut, if you pass a bare string to any of the operation functions, they will assume this is the name of a key and wrap a Set around it. So these three versions are equivalent:

>>> result = rs.Union(rs.Set('key1'), rs.Set('key2'))
>>> result = rs.Union(rs.Set('key1'), 'key2')
>>> result = rs.Union('key1', 'key2')

Rediset also supports an optional "Python-set-like" interface for operations between sets (and other operations):

>>> s1 = rs.Set('key1')
>>> s2 = rs.Set('key2')
>>> s3 = rs.Set('key3')
>>> i = s1.intersection(s2, s3)
>>> u = s1.union(s2, s3)
>>> d = s1.difference(s2, s3)

How does it work?

Set operations are performed using the SUNIONSTORE, SINTERSTORE and SDIFFSTORE commands provided by Redis. The result of an operation on multiple sets is stored in another set in Redis, under a key generated by Rediset.