Randomly select a set number of samples (of size n) without overlap, nor replacement, in a signal

I have a sound signal and I would like to randomly select 5 units of 10 seconds in that signal, but with no overlap, and with no replacement. It looks like I cannot use the function datasample because it only sample 1 sample in the vector (whereas I need: n = 10 seconds * sampling frequency).

If it is possible, I also would like a buffer length of b samples in between each unit sampled.

Any help much appreciated! Thank you!

[Thiago Henrique Gomes Lobato]

Just to be clear, you want to have 5 units of consecutive data each with 10 s and with a distance of b between each point? If so, you just have to randomly define your start point and everything else is already define. Is that right?

[Butterflyfish]

Sorry for the misunderstanding. Let's say the signal is 10 minutes total. I would like to sample 5 units of data randomly in the signal (vector). Each unit would need to be 10 seconds and at least a distance of b between them. The units should not overlap.

[Turlough Hughes]

Find out how many 10 second segments you have, assign a number to each segment and use randperm to get a random 5 samples non repeating. Can you attach the data to the question.

Answer 1

[Image Analyst]

Try this:

% Set up the signal and sampling parameters
samplingFrequency = 100; % Samples per second.
totalSeconds = 6000 % 6000
totalSamples = ceil(totalSeconds * samplingFrequency)
numRequiredSeconds = 10;
numRequiredSamples = ceil(numRequiredSeconds * samplingFrequency)
signal = rand(1, totalSamples);
numRequiredSegments = 5
segmentCount = 0;
iterations = 0;
maxIterations = 100000; % Some huge number where if we reach this, we will assume that the required number of segments can't be found randomly.
% Now look for acceptable non-overlapping segments.
while segmentCount < numRequiredSegments && iterations < maxIterations
	% Get a random starting and stopping points for one segment.
	thisStartingIndex = randi(totalSamples, 1);
	thisStoppingIndex = thisStartingIndex + numRequiredSamples - 1;
	% See if any indexes in this range overlap any prior indexes.
	okay = true;
	if iterations > 0
		for k = 1 : iterations
			% See if starting index is inside any existing segment.
			if thisStartingIndex >= startingIndexes(k) && thisStartingIndex <= stoppingIndexes(k)
				okay = false;
			end
			% See if stopping index is inside any existing segment.
			if thisStoppingIndex >= startingIndexes(k) && thisStoppingIndex <= stoppingIndexes(k)
				okay = false;
			end
		end
	end
	if okay
		% If we get to here, the segment is okay - no overlapping with prior segments.
		% Record the starting and stopping index of this segment, since it's okay.
		segmentCount = segmentCount + 1; % Increment the index of this particular segment.
		startingIndexes(segmentCount) = thisStartingIndex;
		stoppingIndexes(segmentCount) = thisStoppingIndex;
		fprintf('Found a good segment on iteration #%d.  Starting Index = %d.  Stopping Index = %d.\n', ...
			iterations, thisStartingIndex, thisStoppingIndex);
	end
	% Increment the loop counter.
	iterations = iterations + 1;
	fprintf('Done with iteration #%d.\n', iterations);
end
% Optional: sort
[startingIndexes, sortOrder] = sort(startingIndexes, 'ascend');
stoppingIndexes = stoppingIndexes(sortOrder);
% Display sorted indexes in the command window.
for k = 1 : length(startingIndexes)
	fprintf('Segment #%d:  Starting Index = %d.  Stopping Index = %d.\n', ...
		k, startingIndexes(k), stoppingIndexes(k));
end

You'll see in the command window:

Segment #1: Starting Index = 132291. Stopping Index = 133290.

Segment #2: Starting Index = 202347. Stopping Index = 203346.

Segment #3: Starting Index = 371253. Stopping Index = 372252.

Segment #4: Starting Index = 568586. Stopping Index = 569585.

Segment #5: Starting Index = 582577. Stopping Index = 583576.

[Butterflyfish]

This works like a charm! Thank you so much!

[Butterflyfish]

I actually have got an error appearing when the segment has some overlapping, e.g. this output after iteration 1 did not find a non overlapping segment, iteration 2 failed:

Found a good segment on iteration #0.  Starting Index = 17984933.  Stopping Index = 19307932.
Done with iteration #0.
Done with iteration #1.
Index exceeds the number of array elements (1).
Error in ... (line 190)
                if thisStartingIndex >= startingIndexes(k) && thisStartingIndex <= stoppingIndexes(k)

[Image Analyst]

For some reason your starting and stopping indexes are not the same. Make sure your stopping index is not more than the length of the vector.

thisStoppingIndex = min([length(signal), thisStartingIndex + numRequiredSamples - 1]);

Then, just to be sure, limit the for loop

for k = 1 : min([length(startingIndexes), length(stoppingIndexes)]

[Image Analyst]

Can you attach the file that is causing this problems?

[Butterflyfish]

Sorry I erased my last comment by mistake. So the problem is now that I get segments smaller than the required number of samples. Which give me this output, for example:

Found a good segment on iteration #0.  Starting Index = 18586722.  Stopping Index = 19909721.
Done with iteration #0.
Found a good segment on iteration #1.  Starting Index = 16550163.  Stopping Index = 17873162.
Done with iteration #1.
Found a good segment on iteration #2.  Starting Index = 13293809.  Stopping Index = 14616808.
Done with iteration #2.
Found a good segment on iteration #3.  Starting Index = 26312898.  Stopping Index = 26460000.
Done with iteration #3.
Done with iteration #4.
Done with iteration #5.
Done with iteration #6.
Found a good segment on iteration #7.  Starting Index = 21787214.  Stopping Index = 23110213.
Done with iteration #7.
Segment #1:  Starting Index = 13293809.  Stopping Index = 14616808.
Segment #2:  Starting Index = 16550163.  Stopping Index = 17873162.
Segment #3:  Starting Index = 18586722.  Stopping Index = 19909721.
Segment #4:  Starting Index = 21787214.  Stopping Index = 23110213.
Segment #5:  Starting Index = 26312898.  Stopping Index = 26460000.
Unable to perform assignment because the indices on the left side are not compatible with the size of the right
side.

Error in test (line 71)
    segments(:,k) = soundfile(startingIndexes(k):stoppingIndexes(k),1);

Here is a folder with the script and a signal as an example:

dropbox folder with files

Many thanks for your help ! Invaluable!