Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2009

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Re: Re: generating submultisets with repeated

  • To: mathgroup at smc.vnet.net
  • Subject: [mg103741] Re: [mg103700] Re: [mg103681] Re: generating submultisets with repeated
  • From: "Kurt TeKolste" <tekolste at fastmail.us>
  • Date: Sun, 4 Oct 2009 05:37:17 -0400 (EDT)
  • References: <DE9DE45304B6FA4EBE8252CD4EBDA2418286B95F41@PBI-NAMSG-02.MGDPBI.global.pvt>

A simpler trick is to simply repeat all of the elements of the set a
sufficient number of times.  

In[100]:= 
coinSets[set_List, size_Integer] := 
 Union[Subsets[Flatten[ConstantArray[#, size] & /@ set], {1, size}]]

In[101]:= coinSets[{1, 3, 4}, 3]

Out[101]= {{1}, {3}, {4}, {1, 1}, {1, 3}, {1, 4}, {3, 3}, {3, 4}, {4, 
  4}, {1, 1, 1}, {1, 1, 3}, {1, 1, 4}, {1, 3, 3}, {1, 3, 4}, {1, 4, 
  4}, {3, 3, 3}, {3, 3, 4}, {3, 4, 4}, {4, 4, 4}}

In[102]:= coinSets[{1, 3, 4, 9}, 3]

Out[102]= {{1}, {3}, {4}, {9}, {1, 1}, {1, 3}, {1, 4}, {1, 9}, {3, 
  3}, {3, 4}, {3, 9}, {4, 4}, {4, 9}, {9, 9}, {1, 1, 1}, {1, 1, 
  3}, {1, 1, 4}, {1, 1, 9}, {1, 3, 3}, {1, 3, 4}, {1, 3, 9}, {1, 4, 
  4}, {1, 4, 9}, {1, 9, 9}, {3, 3, 3}, {3, 3, 4}, {3, 3, 9}, {3, 4, 
  4}, {3, 4, 9}, {3, 9, 9}, {4, 4, 4}, {4, 4, 9}, {4, 9, 9}, {9, 9, 9}}

In[103]:= coinSets[{a, b, c}, 3]

Out[103]= {{a}, {b}, {c}, {a, a}, {a, b}, {a, c}, {b, b}, {b, c}, {c, 
  c}, {a, a, a}, {a, a, b}, {a, a, c}, {a, b, b}, {a, b, c}, {a, c, 
  c}, {b, b, b}, {b, b, c}, {b, c, c}, {c, c, c}}

ekt



On Sat, 03 Oct 2009 09:01 -0400, "David Bevan" <david.bevan at pb.com>
wrote:
> Daniel,
> 
> Your 'solution' is incorrect since multisets are repeated (e.g. {1,3} and
> {3,1} are both produced). In fact it simply demonstrates the problem. The
> output I want for your example data is:
> 
> {{1},{3},{4},{9},{1,1},{1,3},{1,4},{1,9},{3,3},{3,4},{3,9},{4,4},{4,9},{9,9},{1,1,1},{1,1,3},{1,1,4},{1,1,9},{1,3,3},{1,3,4},{1,3,9},{1,4,4},{1,4,9},{1,9,9},{3,3,3},{3,3,4},{3,3,9},{3,4,4},{3,4,9},{3,9,9},{4,4,4},{4,4,9},{4,9,9},{9,9,9}}
> 
> Btw, who is responsible for the Combinatorica package? Is there some way
> of requesting or perhaps more usefully helping to provide new functions?
> Certainly a (more general) SubMultiset function would perhaps be of use
> to others.
> 
> Thanks.
> 
> David %^>
> ________________________________________
> From: Daniel Lichtblau [danl at wolfram.com]
> Sent: 02 October 2009 16:07
> To: David Bevan
> Subject: [mg103700] Re: [mg103681] Re: generating submultisets with
> repeated elements
> 
> David Bevan wrote:
> > I've now tried the following, which avoids generating the extra multisets:
> >
> >
> > coinSets[s_,k_]:=Flatten[Table[subMultiSets[s,i],{i,k}],1]
> >
> >
> >
> > subMultiSets[s_,k_]:=smsLoop[{},s,k]
> >
> >
> >
> > smsLoop[{ts___},{x_},1]:={{ts,x}}
> >
> >
> >
> > smsLoop[t:{ts___},{x_,xs___},1]:=Prepend[smsLoop[t,{xs},1],{ts,x}]
> >
> >
> >
> > smsLoop[{ts___},s:{x_},k_]:=smsLoop[{ts,x},s,k-1]
> >
> >
> >
> > smsLoop[t:{ts___},s:{x_,xs___},k_]:=Join[smsLoop[{ts,x},s,k-1],smsLoop[t,{xs},k]]
> >
> >
> >
> > Any suggestions for a better approach?
> >
> >
> >
> > David %^>
> >
> >
> > ________________________________
> > From: David Bevan
> > Sent: 01 October 2009 18:57
> > To: mathgroup at smc.vnet.net
> > Subject: [mg103681] generating submultisets with repeated elements
> >
> > I'm new to Mathematica, so if I've missed something obvious, my apologies .
> >
> > I want a function to generate a list of "submultisets" with up to k elements of a set s, allowing elements from s to be repeated.
> >
> > The following works, but is very inefficient since each multiset is generated multiple times and then sorted and then repeats deleted:
> >
> >
> > coinSets[s_,k_]:=DeleteDuplicates[Sort/@Flatten[Tuples[s,#]&/@Range[k],1]]
> >
> >
> >
> > coinSets[{1,3,4},3]
> >
> >
> >
> > {{1},{3},{4},{1,1},{1,3},{1,4},{3,3},{3,4},{4,4},{1,1,1},{1,1,3},{1,1,4},{1,3,3},{1,3,4},{1,4,4},{3,3,3},{3,3,4},{3,4,4},{4,4,4}}
> >
> >
> >
> > I assumed there would be a suitable function in the Combinatorica package, but I can't see anything -- which would be a bit odd for a combinatorial package. What have I missed?
> >
> >
> >
> > Do I need to write my own (perhaps by looking at how KSubsets is implemented) or is there some easy way of generating these multisets?
> >
> >
> >
> > Thanks.
> >
> >
> >
> > David %^>
> 
> Outer can be put to good use here.
> 
> sublists[k_,lst_] :=
>    Flatten[Outer[List,Apply[Sequence,Table[lst,{k}]]], k-1]
> 
> coinSets2[k_,lst_] := Apply[Join, Table[sublists[j,lst], {j,k}]]
> 
> In[23]:= ll = {1,3,4,9};
> 
> In[24]:= InputForm[coinSets2[3,ll]]
> 
> Out[24]//InputForm=
> {{1}, {3}, {4}, {9}, {1, 1}, {1, 3}, {1, 4}, {1, 9}, {3, 1}, {3, 3}, {3,
> 4},
>   {3, 9}, {4, 1}, {4, 3}, {4, 4}, {4, 9}, {9, 1}, {9, 3}, {9, 4}, {9, 9},
>   {1, 1, 1}, {1, 1, 3}, {1, 1, 4}, {1, 1, 9}, {1, 3, 1}, {1, 3, 3}, {1,
> 3, 4},
>   {1, 3, 9}, {1, 4, 1}, {1, 4, 3}, {1, 4, 4}, {1, 4, 9}, {1, 9, 1}, {1,
> 9, 3},
>   {1, 9, 4}, {1, 9, 9}, {3, 1, 1}, {3, 1, 3}, {3, 1, 4}, {3, 1, 9}, {3,
> 3, 1},
>   {3, 3, 3}, {3, 3, 4}, {3, 3, 9}, {3, 4, 1}, {3, 4, 3}, {3, 4, 4}, {3,
> 4, 9},
>   {3, 9, 1}, {3, 9, 3}, {3, 9, 4}, {3, 9, 9}, {4, 1, 1}, {4, 1, 3}, {4,
> 1, 4},
>   {4, 1, 9}, {4, 3, 1}, {4, 3, 3}, {4, 3, 4}, {4, 3, 9}, {4, 4, 1}, {4,
> 4, 3},
>   {4, 4, 4}, {4, 4, 9}, {4, 9, 1}, {4, 9, 3}, {4, 9, 4}, {4, 9, 9}, {9,
> 1, 1},
>   {9, 1, 3}, {9, 1, 4}, {9, 1, 9}, {9, 3, 1}, {9, 3, 3}, {9, 3, 4}, {9,
> 3, 9},
>   {9, 4, 1}, {9, 4, 3}, {9, 4, 4}, {9, 4, 9}, {9, 9, 1}, {9, 9, 3}, {9,
> 9, 4},
>   {9, 9, 9}}
> 
> Daniel Lichtblau
> Wolfram Research
> 
Regards,
Kurt Tekolste



  • Prev by Date: Re: Re: Re: generating submultisets with
  • Next by Date: Prime/Twin Prime Generator
  • Previous by thread: Re: Re: Re: generating submultisets with
  • Next by thread: Prime/Twin Prime Generator