[Newbies] Another extension proposal -> subsets
cdrick
cdrick65 at gmail.com
Wed Jul 23 15:51:50 UTC 2008
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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