How to cut out specific segments from a signal?

Hi all,

Im going nuts. This should be really easy but i've been stuck on it for days.

Let's say I have a signal (vector) x. There are certain parts of x I want removed/extracted so that I leave behind a shorter version of x, without these parts.

I have two vectors defining these unwanted parts. One that defines that start position (remove_start) and another the end position (remove_end).

So the vectors look like:

x = [x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x ...]

remove_start= [11 26 ...] remove_end= [15 31 ...]

I want to get rid of the bold segments in order to get x = [x x x x x x x x x x x x x x], so sticking the non bold bits together. 'x' can take any (real) number.

The problem arises from the fact that when I do something like x(remove_start(i):remove_end(i))=[]; I screw up the timings of remove_start and remove_end. I've tried so many different ways of doing this but none seem to work.

The current way im doing it is:

cut_lag=0;

for i=1:length(remove_start)

    x(remove_start(i)-cut_lag(i):remove_end(i)-cut_lag(i))=[];
    cut_lag(i+1)=cut_lag(i)+remove_end(i)-remove_start(i);

end

So the idea is to keep track of my cutting out the non-wanted bits has shifted the remaining remove times.

This seems to work for the start of x but it eventually degrades and it ends up cutting out the wrong parts...

Plsss helps, thanks so much!!

R

Answer 1

[Star Strider]

If I understand correctly what you want to do, I would begin your loop at the end of the vector and move toward the beginning. That way, you don’t disrupt the other indices.

Something like this:

for i = length(remove_start):-1:1

I didn’t actually run your code, but this is the usual method of removing array elements in a loop without compromising the existing array references.

[Rafael Cordero]

Thank you so much star strider!! I can't believe it was this easy, I want to cry...

[Star Strider]

My pleasure!

Another option is ‘logical indexing’, but I wasn’t sure I understood what you’re doing well enough to suggest it.

An example that removes the three center elements in ‘V’:

V = 1:9                             % Original Vector
idx = (V>3) & (V<7)                 % Logical Vector To Identify Consecutive Elements
Vresult = V(~idx)                   % Use Negation Operator ‘~’ To Remove Those Elements

Run the code snippet to see how it works.

You can remove any number of elements at once from an array this way in one operation.

[Anusshree]

Thank you star

[Star Strider]

@Anusshree — My pleasure!