To Count the reversal of a series of numbers in a column or row.

I have a data with the first column as follows" A = [1 1 1 1 2 2 2 2 3 3 3 4 4 3 3 2 2 2 3 3 3 3 4 4 4 5 5 5 5 6 6 6 6 6 7 7 7 7 8 8 8 7 7 6 6 7 7 7 8 8 8 9 9 9 9 ]; I want to count how many times the number roll back, means, form the beginning the number keep on increasing and after 4 it reversed again after 2 it start increasing. This thing happen after 7 also. So how can I make a code to count how many times it reversed? For example, in this case , the data A reversed two times. In my original data, I have almost 1000 or even more data with several reversals.

Answer 1

[Jos (10584)]

dA = diff(A) ; 
Nreversals = sum(diff(dA(dA~=0))<0)

[aneps]

It was looking good to me but when I applied to the real data it is giving wrong result! For eg. in the attached data, the col 2 or col 4 both reverse only once. So, the result of Nreversals should be 1. Instead the code is giving result 6 if I use A(:,2) and 35 if I use A(:,4).

[Jos (10584)]

Ok! Corrected code:

dA = sign(diff(A)) ;
Nreversals = sum(diff(dA(dA~=0))<0)

Note there are 15 small reversals in column 4 ...