extract and store valuable data in vectors

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Mansour Aljohani 2015-7-25

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评论： Mansour Aljohani 2015-7-27

I have a signal (vector) consists of many blocks (for example five blocks）.I want to extract, separate, these blocks (that contain a valuable information ) from the main signal and store every block in a vector. This is real data and the 5 valuable information in the example are not always in same location.

For example like:

So if I have an input vector (V), The result , in our case, should be five mini vectors (v1, v2, v3, v4, v5).

I tried to apply this method: If a specific consecutive elements from (V) vector have a value above a threshold (for example 0.02 > Thr) start put the elements in a a mini vector, but it does not work because values in the input vector (V) are getting positive and negative.

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Answer 1

Image Analyst 2015-7-26

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在 MATLAB Online 中打开

Simple thresholding won't work because in each burst there are dips that you probably want to keep. Luckily for you I solved this same problem for another person in this discussion: http://www.mathworks.com/matlabcentral/answers/229678#answer_185935 :

% Setup - read in the signal and plot it.
s=load('signal.mat')
signal = s.coarse_d;
subplot(3,1,1);
plot(signal, '-', 'Color', [0,.5,0]);
grid on;
% MAIN CODE IS THE FOLLOWING TWO LINES OF CODE.
% Threshold the signal
lowSignal = abs(signal) < 0.1;
% Remove stretches less than 10,000 elements long.
% And invert it to get the high signal areas instead of the quiet areas.
lowSignal = ~bwareaopen(lowSignal, 10000);
% Now we're done.  Plot the results.
subplot(3,1,2);
plot(lowSignal, 'b-', 'LineWidth', 2);
grid on;
% Plot both on the same graph now.
subplot(3,1,3);
plot(signal, '-', 'Color', [0,.5,0]);
hold on;
plot(lowSignal, 'b-', 'LineWidth', 2);
grid on;

As you can see it identifies each "block" but leaves the inside of the block intact.

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Image Analyst 2015-7-27

I don't think I have that data anymore. I can use yours if you upload it. Like Jan says, because each chunk may be different lengths, it will have to be a cell array, not a regular numerical matrix.

Mansour Aljohani 2015-7-27

TX_DATA.mat

Dear Sir, I attached my data. And thank you so much for your help.

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Answer 2

Jan 2015-7-26

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https://ww2.mathworks.cn/matlabcentral/answers/231181-extract-and-store-valuable-data-in-vectors#answer_187242

编辑：Jan 2015-7-27

在 MATLAB Online 中打开

What about using the absolute value of V?

T          = (abs(V) > Thresh);
blockStart = strfind(T, [false, true]);
blockEnd   = strfind(T, [true, false]);

But even then the signal can have a value below the threshold during a block.

[EDITED]

You can use Fex: RunLength to remove short gaps:

T = (abs(V) > Thresh);
% To fill gaps with less than e.g. 3 frames:
[B, N, Idx] = RunLength(T);
gap         = find((B == false) & (N < 3));   % Two frames
T(gap)      = true;
T(gap+1)    = true;
blockStart = strfind(T, [false, true]) + 1;
blockEnd   = strfind(T, [true, false]);
% Split signal into blocks:
Block = cell(1, length(blockStart));
for k = 1:length(BlockStart)
  Block{k} = V(blockStart(k):blockEnd(k));
end