Googling "smalltalk powerset" turns this up: http://www.foldr.org/~michaelw/log/2005/09/

On Wed, Jul 23, 2008 at 11:51 AM, cdrick cdrick65@gmail.com wrote:

When we don't find method, we reinvent the wheel. Ok, so this is what happened with my quest on rounding float. So here is another example. I needed a method subsets ... to have all subsets of a Set...

#(1 2 ) asSet subsets " -> a Set(a Set(1 2) a Set(1) a Set(2) a Set()) "

Is there already something ? I couldn't find so here is what I did ? probably hackish (because of the binary mask) so feel free to comment ;)

Set>>subsets | subsetsSize subsets workArray | workArray := self asArray. subsetsSize := 2 raisedTo: self size. subsets := OrderedCollection new. 1 to: subsetsSize do: [:ea | subsets add: ((workArray masquedBy: (ea printStringBase: 2)) asSet)]. "masque par une conversion binaire" ^subsets asSet "could be an array of sets"

ArrayedCollection>>masquedBy: aBitString | result entry bitString | entry := self reverse. bitString := aBitString reverse. result := OrderedCollection new. 1 to: (self size) do: [:ea | ((bitString at: ea ifAbsent: []) = $1) ifTrue: [result add: (entry at: ea)]]. ^result reverse

Cédrick

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