How do i count same consecutive occurrences

Consider I have an array of occurrences

A=[1,1,1,1,1,2,2,2,2,3,3,3,3,2,2,2,1,1,1,1]

I want to find out how many 2 are on each occurrence. The answer should be 4 starting 6th position and 3 starting 14 positions.

Is it possible to do it in a wise Matlab way without many loop complications?

Answer 1

[madhan ravi]

https://in.mathworks.com/matlabcentral/answers/77631-how-to-find-the-number-of-consecutive-occurrence-of-the-numbers#answer_87295

Answer 2

[Daniel Pare]

I wanted to count how many time in a row Head or Tail will occure from a random draw and I came up with this.

Let (x) be your vector of observation like x = [1 1 0 1 0 0 0 1]

The result will be: s = [ 2 1 1 3 1]

 s=0 ;
 j=2;
 i=1;
 while i < nb_it+1
    c=1;
    if i == nb_it
        s = [ s c];
        break
    else
        while   x(i) == x(i+1)
                c = c+1;
                i = i+1;
                 if i == nb_it
                    break
                 end
        end            
    end
    
    s = [ s c];
    i = i+1;
 end
 
 s = s(2:end); % to remove the first zero
 sum(s)        % the sum should be equal to the number of element in (x)
 max(s)        % This is the maximum of consecutive ocurence from the draw

[Guillaume]

Or you could do:

 s = diff([0, find(diff(x)), numel(x)]);

and be done...

[Stephen23]

Or similarly:

>> s = diff(find([1,diff(x),1]))
s =
   2   1   1   3   1

[Daniel Pare]

Awesome, and this way takes way less time than doing many loop.

Thanks

[giannit]

That one line command is amazing, many thanks!

[gummiyummi]

I get an error: Error using horzcat. Dimensions of arrays being concatenated are not consistent.

Can anybody help resolve this?

Answer 3

[Bruno Luong]

Example:

A=[1,1,1,1,1,2,2,2,2,3,3,3,3,2,2,2,1,1,1,1]

Code

d = diff([0, A==2, 0]);
startidx = find(d==1)
lgt = find(d==-1)-startidx % EDIT error

Result

startidx =

     6    14


lgt =

     4     3

[gummiyummi]

I still get the same error...

[Bruno Luong]

@As Sc: Can you tell if your A is a row vector? column vector? Something else?

Please type

class(A)
size(A)

then report the result. A is your array.

[Ayush Meena]

@Bruno can you please tell me what is idx here?

[Bruno Luong]

@Ayush Meena it's a typo, should be startidx.