Class: PowerSet

• Inheritance
• Description
• Related information
• Class protocol
  • instance creation
• Instance protocol
  • enumerating
  • initialization
  • queries
• Examples

Inheritance:

   Object
   |
   +--Collection
      |
      +--PowerSet

Package:

stx:libbasic2

Category:

Collections-Unordered

Version:

rev: 1.5 date: 2014/02/23 01:14:33

user: cg

file: PowerSet.st directory: libbasic2

module: stx stc-classLibrary: libbasic2

Author:

Claus Gittinger

Description:

A PowerSet of a collection is the set of all possible (sub-)collections
built from the original collection's elements.
This includes the empty collection.

The PowerSet of [1 2 3] is therefore:
    []
    [1]
    [2]
    [3]
    [1 2]
    [1 3]
    [2 3]
    [1 2 3]

As the powerset can quickly become huge in size (for a baseSet of n elements, we
get a powerSet size of 2^N), the elements of the powerset are created dynamically.
I.e. they are only created on demand.
As this, this is a good example of polymorphism: powerSets represent collections,
but do not really store their elements (see Interval for another such Collection).

Related information:

    Set
    Interval

Class protocol:

 for: aCollection

Create & return a new instance for aCollection.

Instance protocol:

 do: aBlock

evaluate the argument, aBlock for each element

 initializeFor: aCollection

 includes: aCollection

(comment from inherited method)
return true, if an element equal to the argument, searchedElement is in the collection.
This compares using #= (i.e. it does not look for the object itself,
instead, one that compares equal).
See #includesIdentical: when identity is asked for.
This is a *very* slow fallback - many subclasses redefine this for performance.

 size

Examples:

    |s p|

    s := #(1 2 3).
    p := PowerSet for:s.

    p do:[:eachSubSet |
        Transcript showCR:eachSubSet
    ].

    |s p|

    s := (1 to:1000).
    p := PowerSet for:s.

    Transcript show:'p''s size is: '; showCR:p size

    |s p|

    s := (1 to:10).
    p := PowerSet for:s.
    p includes:#(1 2 3) asSet.   
    p includes:#(1 2 4) asSet.   
    p includes:#(0 1 2) asSet.