Number of sequences with 3 or more ascending numbers

Hello,

I have following problem:

I have to find number of sequences occuring in vector. Such sequence contains 3 or more numbers which are ascending

so, for examplet

v = [ 1 8 2 5 8 0 0 1 2 3 4 9]

in this vector, such sequence occurs 2 times: 2 5 8 AND 0 1 2 3 4 9.

I would like to have these sequences stored in separate vector.

So far i have tried this:

v = [ 1 8 2 5 8 0 0 1 2 3 4 9]
n_sequences=0
 for k = 1:length(v)
    if v(k)<v(k+1)<v(k+2)<v(k+3)
    n_sequences= n_sequences + 1   
    end
 end

However this doesnt work as I supposed. I am not sure how to incorporate "3 OR MORE" into code.

Thanks,

Answer 1

[Matt J]

all( diff(v(k:k+2)) >= 0 )

[Avish Sjavi]

Thanks, but i am not sure how to incorporate this to my code

[Matt J]

It tests whether you have 3 increasing elements in a row, as you asked for. Examples:

>> v = [ 1 8 2 5 8 0 0 1 2 3 4 9]

v =

     1     8     2     5     8     0     0     1     2     3     4     9

>> k=3;
>> all( diff(v(k:k+2)) >= 0 )

ans =

  logical

   1

>> k=4;
>> all( diff(v(k:k+2)) >= 0 )

ans =

  logical

   0

>> k=6;
>> all( diff(v(k:k+2)) >= 0 )

ans =

  logical

   1

Answer 2

[Andrei Bobrov]

lo = diff(v) > 0;
lo = [~lo(1);lo];
lo2 = [lo(2:end);false]|lo;
i = cumsum(lo == 0 & lo2).*lo2;
j = accumarray(i + 1,1);
C = accumarray(i + 1,(1:numel(v))',[],@(x){v(x)});
out = C(J >= 3);