How can I count the followed occurrences of each element in a vector in MATLAB?

Hi, I want to count the number of followed occurrences of each element in a vector.

So if my input is

x = [1 1 1 2 2 1 1 2 5 5]

I need an output

y = [1 2 1 2 5;3 2 2 1 2] How do I do this?

[William]

check out this post : http://www.mathworks.com/matlabcentral/answers/34302-how-to-find-consecutive-numbers

[lamghari]

thank's William But this post concerns the consecutive numbers (x + 1) !! I need the occurrence of the same numbers followed

Answer 1

[Stephen23]

Judicious use of diff solves this easily:

x = [1 1 1 2 2 1 1 2 5 5];
f = [find(diff(x)),numel(x)];
y(2,:) = [f(1),diff(f)];
y(1,:) = x(f);

which generates this output:

>> y =
      1   2   1   2   5
      3   2   2   1   2

[lamghari]

Thanks Stephen, that works!

[lamghari]

and if I want to reverse the operation: I have a two-line matrix: the first line contains the numbers and second occurrences. I want to convert it to a vector my inpout is for example:

A= 1 2 1 2 5; 3 2 2 1 2 i need an outpout: y = 1 1 1 2 2 1 1 2 5 5

[Stephen23]

If you have a newer MATLAB version, you can use repelem, which provides exactly this functionality:

repelem(A(1,:),A(2,:))

Otherwise use arrayfun and repmat:

>> A = [1,2,1,2,5; 3,2,2,1,2];
>> C = arrayfun(@(v,n)repmat(v,1,n),A(1,:),A(2,:),'UniformOutput',false);
>> B = horzcat(C{:})
B =
   1   1   1   2   2   1   1   2   5   5

[lamghari]

thanks a lot for your cooperation :)

Answer 2

[Jan]

If run time matters, you can try FEX: RunLength

x      = [1 1 1 2 2 1 1 2 5 5];
[b, n] = RunLength(x);
Result = [b; n];

[lamghari]

Thank you Jan