如何在数组中找到最后一个非零的元素的索引

Question

I have a vector d that its size 1x1000 . It stores a random values from 0 to 1 . For example

d=[0.0076 0.4629 0.1554...0 0 0 0 ...0.0442 0 0 0 10^-7 10^-7 10^-7] 

Now, I want to get the index of element at the last of vector (has maximize index) subject to non-zero or bigger than 10^-7 ). For my example, the element that has value is 0.0442 and index= ?. How to implement it by MATLAB? Thank all

Answer 1

To find the last element that satisfies a condition, you can use the syntax find(tf, 1, 'last') .

In your case, you want to find the last value that is more than a certain tolerance away from zero, ie

tol = 2e-7;
idx = find( abs(d)>tol, 1, 'last');

Note: I've used abs(d) so that the solution is robust to negative values in the input, and I set the tolerance to 2e-7 to increase the likelihood that the threshold is in between the most likely good values and the most likely bad values (setting it to 1e-6 may be even safer).

Answer 2

 ind = find(d ~= 0);
 ind(end) = % last nonzero index
 d(ind(end)) = % last nonzero element

You can add threshold: ind = find(d > 1e-7)

If you also have negative data you may add threshold like ind = find(d > 1e-7 | d < -1e-7)

Answer 3

You can use a combination of max and cumsum -

tol = 1e-7; %// tolerance value
[~,index] = max(cumsum(d>tol))