Count number of changes to 1

Hi, I have got a binary vector which looks like this: vec = [0 0 0 1 1 0 0 0 0 1 1 1 1 1 1 0 0 1 1 1 1 0 0 0 0 0 1 1 1 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 1 0 0 0 ] I would like to know how many times it changes to 1. In this case six times.

I have tried it by first counting the number of changes: r=sum(abs(diff(vec))) and then devide it by 2. This will work when I have got an equal number of changes to 1 and changes to 0, but this is unfortunately not always the case.

What is the best way to do solve this in matlab?

Many thanks.

Answer 1

[Daan]

Thank you both, but I still have one problem. I have also got binary vectors which start with a 1 like: v= [1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 0 0 0] and I want to get eventually the number of streaks of the number 1 (in this case 3). When I determine the number of changes the first streak of 1's isn't counted. How can I solve this problem?

Thanks in advance.

[Thorsten]

Just add a 0 in front of the vec

N = sum(diff([0 vec]) == 1));

Answer 2

[Image Analyst]

Get rid of the abs(). Just simply do this:

vec = [0 0 0 1 1 0 0 0 0 1 1 1 1 1 1 0 0 1 1 1 1 0 0 0 0 0 1 1 1 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 1 0 0 0 ]
d = diff(vec)
numChangesTo1 = sum(d == 1)

[MA-Winlab]

In my case, if I have similar vector with blocks of 0s and blocks of 1s, I want to find the index(s) at which a change from 1 to 0 happens(store them in a vector) and the index(s) at which a change from 0 to 1 happens (returing them in a seprate vector).

Your comments are appreciated

UPDATE:

SW =[1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0       1     1      1      1       1]

I used ischange, but it only returns 1s in the places for both: changes when there is change from 1 to 0 and similarly, when there is change from 0 to 1. In this case, I am not able to know if the change was from 0 to 1 or from 1 to 0, I only know that there was a change.

[MA-Winlab]

Update

I figured out how to do that (in my case, the vector of 0s and 1s has an even number):

OpenClose = find(diff(sign(A))) + 1;

OneToZero = OpenClose(1:2:end)

ZeroToOne = OpenClose(2:2:end)

Answer 3

[Nobel Mondal]

If you're only counting the changes 0 -> 1 , then it would be the number of occurrences of 1 (1-0) in the diff vector.

 >> A = [0 0 0 1 1 0 0 0 0 1 1 1 1 1 1 0 0 1 1 1 1 0 0 0 0 0 1 1 1 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 1 0 0 0 ];
 >> count = length(find(diff(A) == 1));

Your code is actually counting the overall number of value changes in the vector. Hope this helps.

Answer 4

[Image Analyst]

Daan:

If you want the number of streaks in a vector like v= [1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 0 0 0], then, if you have the Image Processing Toolbox, simply do this:

[L, numberOfStreaks] = bwlabel(v);

numberOfStreaks will be 3 since you have 3 separate sections of 1's. Also, each streak will have a unique ID number, given in the L vector, in case you need to use that.

Answer 5

[Mitchell Evan]

Hey, So It looks like I'm pretty late to the game and my solution is pretty hacky but it works!

I had a similar situation where I needed to count the numer of times a signal went from 1 to -1.

count("1 -1",string(sign(vec))) 
%so for you count
("0 1",string(sign(Zeroed'))) 

It counts the number of occurances of that input pattern string.

String methods for the win!

Answer 6

[Image Analyst]

By far the simplest answer is to simply use strfind. It's a single line of code. It's a little known trick that strfind works for numerical arrays as well as character arrays:

vec = [0 0 0 1 1 0 0 0 0 1 1 1 1 1 1 0 0 1 1 1 1 0 0 0 0 0 1 1 1 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 1 0 0 0 ];
numChangesTo1 = numel(strfind(vec, [0, 1])) % Find and count 0-to-1 sequences.

numChangesTo1 = 6