Do calculations for lines that are true

How can I make matlab do a calculation, that will require a previous line, for a condition being true? Please reference the file I've attached.

When the 'z' vector is true, or 1, I want to take the current line's 'v', and subtract the previous line's 'v'. Then, if the next line is also true, to do the same calculation; so on and so forth until z = 0.

I will then want to take an average over each given interval of z being true, and put that into a new vector.

Any help is appreciated!

[jonas]

And what do you want to do when the z(1)==1? There is no previous line.

[Dylan Mecca]

It can be disregarded. I understand that there can't be a calculation there.

[Dylan Mecca]

I'll change the document to have that z(1) to be a zero to make answering this question a little easier. It isn't critical to my application.

[jonas]

abs=xlsread('absbreak.xlsx');

v=abs(:,2)

z=abs(:,3)

ind=find(z==1)

v(ind)=v(ind)-v(ind-1)

I probably misinterpreted your request. Do you want v to update while you loop over the data?

[Dylan Mecca]

'v' should not be updated, but the answers from the calculation derived from 'v' should be averaged then stored into another vector.

On a side note, can I ask why you suggest using abs?

[jonas]

'abs' is just a poorly chosen variable name that I got from the name of the excel-file, it has nothing to do with the function abs().

If you want to average the data then I suggest that you use find(z==0), which will give you 4 indices over which you can then average.

There is probably a much better way but I am still not entirely sure what you want to do. For example, do you want to include the v-values of z being zero? Otherwise the average is obviously 1.

[Guillaume]

Can you explain a lot better what it is you want to do. For your given file, what should the output be?

[Dylan Mecca]

Output should have a new vector of average 'v' only where z = 1.

For instance, cells 3:9 have 'z' as true. Take the average of 'v' during that interval, and store that average value as the first value in a new vector.

Do the same for cells 11:16, where that average will be stored as the second value in the new vector.

And finally, do it for a third vector value for average value of 'v' where 'z' = 1 in cells 19:22.

I can build a hard code to satisfy these cell values, but I need help developing a way to make matlab see the pattern I', trying to explain.

Answer 1

[Rik]

If you have the Image Processing Toolbox, you can use bwlabel to label each group of indices where z is 1. If you don't have this toolbox, this wikipedia page could help.

data=xlsread('absbreak.xlsx');
v=data(:,2);
z=data(:,3);
[labels,num]=bwlabel(z==1);
avg_vec=zeros(1,num);
for n=1:num
    avg_vec(n)=mean(v(labels==n));
end

[Rik]

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