Question

Okay, this might seem like a weird question, but bear with me.

So I have a random vector in a .m file, with certain constraints built into it. Here is my code:

 randvecall = randsample(done, done, true);
 randvec = randvecall([1;diff(randvecall(:))]~=0);

“Done” is just the range of values we take the sample from, so don’t worry about that. As you can see, this randsamples from a range of values, and then prunes this random vector with the diff function, so that consecutive duplicate values are removed. There is still the potential for duplicate values in the vector, but they simply cannot be consecutive.

This is all well and good, and works perfectly fine.

So, say, randvec looks like this:

randvec =

    54
    47
    52
    26
    39
     2
    14
    51
    24
     6
    19
    56
    34
    46
    12
     7
    41
    18
    29
     7

It is actually a lot longer, with something like 60-70 values, but you get the point.

What I want to do is add a little extra constraint on to this vector. When I sample from this vector, the values are classified according to their range. So values from 1-15 are category 1, 16-30 are category 2, and so on. The reasons for this are unimportant, but it is a pretty important part of the program. So if you look at the values I provided above, you see a section like this:

     7
    41
    18
    29
     7

This is actually bad for my program. Because the value ranges are treated separately, 41, 18, and 29 are used differently than 7 is. So, for all intents and purposes, 7 is appearing consecutively in my script. What I want to do is somehow parse/modify/whatever the vector when it is generated so that the same number from a certain range cannot appear twice “in a row,” regardless of how many other numbers from different ranges are between them. Does this make sense/did I describe this well? So, I want MATLAB to search the vector, and for all values within certain ranges (1-15,16-30,31-45,46-60) make sure that “consecutive” values from the same range are not identical.

So, then, that is what I want to do. This may not by any means be the best way to do this, so any advice/alternatives are, of course, appreciated. I know I can do this better with multiple vectors, but for various reasons I need this to be a single, long vector (the way my script is designed it just wouldn’t work if I had a separate vector for each range of values).

Answer 1

What you may want to do is create four random vectors, one for each category, ensure that they do not contain any two consecutive equal values, and then build your final random vector by ordered picking of values from random categories, i.e.

%# make a 50-by-nCategories array of random numbers
categories = [1,16,31,46;15,30,45,60]; %# category min/max
nCategories = size(categories,2);
randomCategories = zeros(50,nCategories);

for c=1:nCategories
   %# draw 100 numbers for good measure
   tmp = randi(categories(:,c),[100 1]);
   tmp(diff(tmp==0)) = []; %# remove consecutive duplicates

   %# store
   randomCategories(:,c) = tmp(1:50);
end

%# select from which bins to pick. Use half the numbers, so that we don't force the 
%# numbers of entries per category to be exactly equal

bins = randi(nCategories,[100,1]);

%# combine the output, i.e. replace e.g. the numbers
%# '3' in 'bins' with the consecutive entries
%# from the third category
out = zeros(100,1);
for c = 1:nCategories
   cIdx = find(bins==c);
   out(cIdx) = randomCategories(1:length(cIdx),c);
end