Find duration of signal

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Marc Elmeua 2020-9-9

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评论： Xavier 2020-9-10

I have a set of signals that due to some unknown error have been acquired with millions of empty datapoints. Is there a way I can automatically detect the moment the signal ends so I can delete everything from that point onwards?

Thanks everyone.

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Star Strider 2020-9-9

在 MATLAB Online 中打开

There are no actual ‘missing’ values, just a very low amplitude signal after about element 40:

T1 = readtable('sampledata.csv');
figure
semilogy(abs(T1{:,1}))
grid

producing:

That would appear to be legitimate data.

.

Xavier 2020-9-10

This depends on how you define legitimate data, if you unplug a probe/sensor from an oscilloscope it will continue to display numbers and a waveform. If you're trying to measure a signal then it is fair to call recorded noise invalid data

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Answer 1

Xavier 2020-9-10

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Something like this may work for you

Raw data:

data = readmatrix('sampledata.csv');
avgdat = movmean(abs(data), 5);
threshold = 0.01;
data(avgdat < threshold) = [];
plot(data)

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Marc Elmeua 2020-9-10

This worked perfectly!! thanks a lot.

Xavier 2020-9-10

No problem!

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Answer 2

Steven Lord 2020-9-9

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https://ww2.mathworks.cn/matlabcentral/answers/591181-find-duration-of-signal#answer_492172

在 MATLAB Online 中打开

If the empty data points are represented by NaN then find the 'last' 1 element of the vector that isfinite.

x = [1:10 NaN(1, 5)]
find(isfinite(x), 1, 'last')

If the vector has no missing data inside it, you could instead just rmmissing.

rmmissing(x)

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Marc Elmeua 2020-9-9

Thanks for the reply! The missing values aren't really missing in the matlab file. They are missing in the original data collection software but as soon as you retrieve them, they turn into zeros so this code will not work :(

I'm in touch with the developers of the software but they still haven't been able to solve this.

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