Finding column index of the first instance of 1

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Pelajar UM 2022-5-2

评论： Walter Roberson 2022-5-3

I have a logical array like this:

I want to extrat the colum index of the cells where the first instance of 1 is detected. Like this:

For example, you see here that the first two rows show 4, because that is where 1 is first detected.

Walter Roberson 2022-5-2

C = sum(cumprod(~X, 2),1) + 1;

C will be one more than the number of columns for any row that has no 1.

Pelajar UM 2022-5-3

编辑：Pelajar UM 2022-5-3

Thanks @Torsten. The second line gives a warning:

Unexpected use of '[' in a scalar context.

And it appears to break the loop already in k=1.

Instead we can use

if isempty(idx) == 1
    break
end

But checking idx in every loop takes longer.

Method 1: 22 seconds

Method 2: 528 seconds

Walter Roberson 2022-5-3

isempty(idx)

Jonas 2022-5-2

use the find() function together with a loop over each row

Pelajar UM 2022-5-2

编辑：Pelajar UM 2022-5-2

Like this?

Doesn't work, because it doesn't find the first instance. It finds all the indices that meet this condition.

for p=1:n %n is the length of the logical array X
    G(p,:)=find (X(p,:));
end 

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