Count number of changes to 1

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Daan
Daan on 16 Sep 2015
Answered: Image Analyst on 22 Sep 2022
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.

Accepted Answer

Daan
Daan on 16 Sep 2015
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.
  1 Comment
Thorsten
Thorsten on 16 Sep 2015
Just add a 0 in front of the vec
N = sum(diff([0 vec]) == 1));

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More Answers (5)

Image Analyst
Image Analyst on 16 Sep 2015
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)
  2 Comments
MA-Winlab
MA-Winlab on 7 Apr 2019
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)

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Nobel Mondal
Nobel Mondal on 16 Sep 2015
Edited: Nobel Mondal on 16 Sep 2015
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.

Image Analyst
Image Analyst on 16 Sep 2015
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.

Mitchell Evan
Mitchell Evan on 22 Sep 2022
Moved: Image Analyst on 22 Sep 2022
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!

Image Analyst
Image Analyst on 22 Sep 2022
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

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