How do I alter a row of numbers based on when the number changes?

I have an array of approximately 80 000 numbers, and I'd like to know how many consecutive numbers of each type there are, and if that number is less than 10000 make those values the same as the previous integer.

For example on a smaller scale when any integer appeared less than 5 times it became the same as the previous value:

8 8 8 8 8 7 7 7 7 7 6 6 6

Would become

8 8 8 8 8 7 7 7 7 7 7 7 7

both 8 and 7 appear 5 times in the original list so would remain unchanged, but 6 only appears 3 times so it becomes 7 for all 3 values.

Many thanks

[Azzi Abdelmalek]

Your example is not clear. Why the result is not: [8 8 8 8 8 8 8 8 8 8 8 8 8]?

[Olivia Lynes]

Sorry, I scaled it down for purposes of providing an example.

So if I was setting it so that when any integer appeared less than 5 times it became the same as the previous value the result becomes

8 8 8 8 8 7 7 7 7 7 7 7 7

both 8 and 7 appear 5 times in the original list so would remain unchanged, but 6 only appears 3 times so it becomes 7 for all 3 values.

[Roger Stafford]

There is still a lack of clarity here. With your "5 times" criterion what would

8 8 8 8 8 7 7 7 7 7 6 6 6 3 3 3 1 1 1

become? Would it be

8 8 8 8 8 7 7 7 7 7 7 7 7 7 7 7 7 7 7

or

8 8 8 8 8 7 7 7 7 7 6 6 6 6 6 6 6 6 6

or

8 8 8 8 8 7 7 7 7 7 7 7 7 3 3 3 3 3 3

or something else? The problem you face in making your request clear is that altering one series of numbers has an effect on adjacent numbers. That needs to be specified in a precise manner.

[Olivia Lynes]

My apologies, not being able to word it is I think what's stopping me from working it out.

To use your example:

8 8 8 8 8 7 7 7 7 7 6 6 6 3 3 3 1 1 1

would become

8 8 8 8 8 7 7 7 7 7 7 7 7 7 7 7 7 7 7

so beyond 6 in the list all numbers would become 7 until the next set of consecutive integers which is greater than 5.

In the following list

8 8 8 8 8 7 7 7 7 7 6 6 6 3 3 3 3 3 1

It would become

8 8 8 8 8 7 7 7 7 7 7 7 7 3 3 3 3 3 3

Hopefully that is clearer, many thanks.

[MHN]

Two questions and I will answer your question: 1- what if the first number occurs less than 5 times? 2- Are the numbers consecutive? i.e. if there is [6 6 6 5 5 ...] is there any 6 in ... part? If no, there is an easy way to do what you want.

Answer 1

[Ced]

Maybe something like this? Not pretty, but not fully brute force either. Since you are looking at fairly big chunks (1000), this should be quite fast.

For any order:

a = [8 8 8 8 8 7 7 7 7 7 6 6 6 3 3 3 1 1 1 0 0 0 0 0];
N = 5;
M = length(a);

ind = 1;
while ( ind <= M )
    % are the next N numbers the same?
    if ( all( a(ind) == a(ind:min(M,ind+N-1)) ) ) % if yes, skip ahead
        ind = ind + N;
        while ( ind <= M && a(ind) == a(1) ) % while the next one is the same
            ind = ind + 1;
        end
    else % if no, set all numbers the same, skip ahead
        a(ind:min(M,ind+N-1)) = a(max(1,ind-1));
        ind = ind + N-1;
    end
end

Note that these weird min/max expressions are only there to make sure I don't run over the boundaries (I hope I didn't miss anything).

Now if they are sorted, I'm sure you can find tricks to avoid (almost) any loops. E.g if you want to count the occurrences and see which ones you have to replace:

a = [8 8 8 8 8 7 7 7 7 7 6 6 6 3 3 3 1 1 1 0 0 0 0 0];
M = length(a);
N = 5;

% get indices of changing numbers
[ unique_num, index, rev_index ] = unique(a,'stable'); 

% See how many are consecutive by looking at difference
% calculate last one with distance from end
N_occurrence = [ diff(index) ; length(a)-index(end) + 1 ];

% These numbers need to be fixed:
fix_numbers = (N_occurrence < N);

% now fix numbers, etc.

Good luck!