# Converting values to 0 and 1 and then counting occurrences!

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adi kul on 26 May 2015
Edited: Andrei Bobrov on 27 May 2015
Hello, I am stuck with a problem.
I have a 200x1 matrix containing values ranging from 0 to 30.
Now I want to convert the values which are less than 20 to zero and values greater than zero to 1.
After doing that I want to count how many occurrences are there when 1 is followed by zero and give the counting as an output!
##### 1 CommentShowHide None
adi kul on 26 May 2015
I am having 5 .mat files. Each mat file contains 5 parameters. A,B,C,D,E. The 5 files are named Trial1.mat, ....., Trial5.mat
I want to take B variable which is of a size 200x1 from each mat file, convert values less than 20 to 0 and greater than 20 to 1.
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Now I want to check how many times 1 is followed by 0.
I want to count this occurrence for each .mat file and give an output file which will give number of count per mat file.
Here is the for loop available to put the code:
if ~isdir(myFolder)
errorMessage = sprintf('Error: The following folder does not exist:\n%s', myFolder);
uiwait(warndlg(errorMessage));
return;
end
filePattern = fullfile(myFolder, '*.mat');
matFiles = dir(filePattern);
for k = 1:length(matFiles)
end
I hope now you got my question!

Thorsten on 26 May 2015
A(A<20) = 0;
A(A>0) = 1;
cnt = sum(diff(A) == -1);
adi kul on 27 May 2015
This helped but can we count only change??
I mean instead of 0 followed by 1 there are some 1 followed by zero at the end which are not being counted. So what to do to count total 0 to1 and 1 to 0 changes???

### More Answers (3)

Sebastian Castro on 26 May 2015
Edited: Sebastian Castro on 26 May 2015
Suppose your original data is named x. The following line will create a matrix the same size as your original, where the elements are 1 if the logical condition is met and 0 otherwise:
xThresh = x>=20
Then, you can use the diff function to get the difference between consecutive elements. You know that a transition from 1 to 0 is a difference of -1, so you can find all the -1s and add them up:
xDiff = diff(xThresh)
numTransitions = sum(xDiff==-1)
- Sebastian
##### 2 CommentsShowHide 1 older comment
adi kul on 27 May 2015
I tried this. But problem is, when there is not "B" column available, it still gives me some value!!

Andrei Bobrov on 26 May 2015
Edited: Andrei Bobrov on 27 May 2015
out = numel(strfind(A(:)' >= 20,[1, 0]));

Ingrid on 26 May 2015
is this what you mean as it is not clear to what end you would like to do this
x(x<20) = 0;
x(x>=20) = 1;
temp = diff(x);
answer = sum(temp == -1);