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Re: Binary Vector Manipulation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg84103] Re: Binary Vector Manipulation
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Mon, 10 Dec 2007 20:34:41 -0500 (EST)
  • Organization: The Open University, Milton Keynes, UK
  • References: <fjj183$frv$1@smc.vnet.net>

Tara.Ann.Lorenz at gmail.com wrote:
> I am need of assistance programming the following scenario:
> 
> I have two vectors composed of 0's and 1's.  Vector "A" has 5% 1's
> (and 95% 0's) while Vector "B" has 50% 1's and 50% 0's.
> 
> First, I would like to change Vector B to have a "1" in every place
> that Vector A also has a "1" (in other words, I will then have more
> than 50% 1's in Vector B once this step is completed).
> 
> Then, I would like to *randomly* return Vector B back to a 50/50
> distribution of 1's and 0's.
> 
> I greatly appreciate any proposed programming methods.

The following function should do what you are asking for.

In[1]:= myFun[A : {0 | 1 __}, target : {0 | 1 __}] /;
   Length@A <= Length@B && EvenQ[Length@B] :=
  Module[{B, len, pos},
   B = target;
   len = Length@B;
   B = ReplacePart[B, Position[A, 1] -> 1];
   While[Count[B, 1] - len/2 > 0,
    pos = RandomInteger[{1, len}];
    If[B[[pos]] == 1, B[[pos]] = 0];
    ];
   B
   ]

Then, we make up some data and check that myFun works correctly.

In[2]:= Needs["Combinatorica`"]
A = RandomPermutation[Join[Table[1, {5}], Table[0, {95}]]];
B = RandomPermutation[Join[Table[1, {50}], Table[0, {50}]]];
c = myFun[A, B];
c == B
Count[#, 1] & /@ {A, B, c}

Out[6]= False

Out[7]= {5, 50, 50}

Regards,
-- 
Jean-Marc



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