[Newbies] Re: Another extension proposal -> subsets
Zulq Alam
me at zulq.net
Wed Jul 23 16:47:26 UTC 2008
Couldn't find anything obvious but remembered #permutationsDo: which may
help. Not sure if these does what you want, but maybe it can be adapted?
Set>>subsets
| subsets |
subsets := Set with: self.
self asArray permutationsDo: [:e | subsets add: e asSet].
self do: [:e | subsets addAll: (self copyWithout: e) subsets].
^ subsets
#(1 2) asSet subsets.
"a Set(a Set(1 2) a Set() a Set(2) a Set(1))"
#(1 2 3) asSet subsets.
"a Set(a Set(1 2) a Set() a Set(2) a Set(1 2 3) a Set(2 3) a Set(3) a
Set(1 3) a Set(1))"
Z.
cdrick 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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