Only keep positve values from a matrix and plot the last of those values.

Hello

I have a matrix (1001x50001) and I want to plot the last potive value of each column. The problem is that the last positve value changes position every now and then to the next row.

How do I plot a graph of these value?

I have tried to save all the positve elements from the matrix as a new variable, but I end up with a very long vector.

sPositive = s(s>0)

Answer 1

[Ameer Hamza]

try this

s = randn(100, 200); % random vector
[~,r] = max(flipud(s)>0);
r = size(s,1)-r+1;
c = 1:size(s,2);

idx = sub2ind(size(s), r, c);
s_positive = s(idx);

s_positive is the first positive value in each column.

[Mikkel Christensen]

I'm having trouble implementing this.

What is the meaning of? Can't get it to fit the dimensions.

[~,r] = max(s>0, [], 1);

[Ameer Hamza]

I edited the code in my answer. Do you get any error at this line?

[Mikkel Christensen]

Yes, I think it's r that's causing a size error.

I am getting "Error using sub2ind. The subscript vectors must all be of the same size."

[Ameer Hamza]

Oh! I overlooked the case that your matrix is rectangular and not square. I have updated my code. Now it should run fine.

[Mikkel Christensen]

Ahh, yea now it works without error!

However, it choose the maximum value of s, when I want the last positive element of each coloumn. It tends to be the minimum value of each coloumn, but when I replace "max" with "min", it doesn't work. Is this wrong?

[Ameer Hamza]

Ok. I misread the question. Please check the updated code.

[Mikkel Christensen]

That's amazing, that did the trick.

Thank you very much!!!

[Ameer Hamza]

Great. I am glad to be of help.