Division of array into subarrays depending on the threshold value

Question

Gova ReDDy 2014-1-11

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/112104-division-of-array-into-subarrays-depending-on-the-threshold-value

编辑： Gova ReDDy 2014-1-14

Hello,

I want to divide a array of signal into sub arrays such that each sub array contains values greater than the threshold(let say 0.08 for each case) untill it encounters again an increment from the threshold.

The subarray should contain the values in between the two thresholds as shown in the figure

can someone explain of how to do it.

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Answer 1

Image Analyst 2014-1-11

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https://ww2.mathworks.cn/matlabcentral/answers/112104-division-of-array-into-subarrays-depending-on-the-threshold-value#answer_120609

在 MATLAB Online 中打开

In your duplicate thread, I explained how to do it. Threshold

nonZeroElements = signal > 0;

Then use diff to look for where the hump starts and stops.

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Image Analyst 2014-1-11

在 MATLAB Online 中打开

If you need it explained in extreme detail in a full blown demo, see this:

clc;
clear all;
% Create sample data for Gova.
t = 1:300;
period = 40;
y = sin(2*pi*t/period);
y = max(0, y)
% Prefix a 0 so we can find the first element.
% Append a 0 so we can find the last element.
y = [0, y, 0];
subplot(2, 1, 1);
plot(y, 'bo-');
grid on;
title('Original Signal', 'FontSize', 24);
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off') 
% Find out where the signal is not zero.
nonZeroElements = y > 0; % Logical vector of 0's and 1's
% Find out indexes where it goes from 0 to 1 or 1 to 0.
diffPattern = diff(nonZeroElements);
% Plot it.
subplot(2, 1, 2);
plot(diffPattern, 'bo-');
grid on;
title('Difference Signal', 'FontSize', 24);
% Find out where every hump starts and stops.
humpStarts = strfind(diffPattern, [1, 0])+1
humpEnds = strfind(diffPattern, [-1, 0])
% Loop through all humps extracting each segment into a cell
for hump = 1 : length(humpEnds)
  indexRange = humpStarts(hump) : humpEnds(hump);
  ca{hump} = y(indexRange);
end
% Display the cell array
celldisp(ca)

Gova ReDDy 2014-1-13

在 MATLAB Online 中打开

Thanks.I tried alot to divide the original signal into sub signal such that each divided array contains the values of signal(from the start of one hump to next hump) looking for a signal in every 50 values of the original signal as shown below

clc;
clear all;
t = 1:300;
period = 40;
y = sin(2*pi*t/period);
y = max(0, y)
y = [0, y, 0];
k=0;a=1;h=1;j=1;
for i=1:50:length(y)-50
    if(i<50)
        x1=y(1,i:i+49);
        input(1,i:i+49)=y(1,i:i+49);
        nonZeroElements = x1 > 0; 
        diffPattern = diff(nonZeroElements); 
        humpStarts = strfind(diffPattern, [1, 0]);
            if (length(humpStarts)>1)   
                for p=1:1:length(humpStarts)-1;
                        k=humpStarts(p);
                        for m=k:1:humpStarts(p+1);
                            needed{a}(1,m)=x1(m); 
                        end;
                        check{j}=p;
                        j=j+1;
                        a=a+1;
                end;
                next(1,1:length(x1)-(m))=x1(1,m+1:length(x1)); 
            elseif(length(humpStarts)==1)
                m=humpStarts(1);  
                next(1,1:length(x1)-(m))=x1(1,m+1:length(x1));               
            else       
                next(1,humpStarts(1):length(x1))=x1(1,humpStarts(1):length(x1));           
            end;       
    else
        x1=y(1,i:i+49);
        input(1,i:i+49)=y(1,i:i+49);
        nonZeroElements = x1 > 0; 
        diffPattern = diff(nonZeroElements); 
        humpStarts = strfind(diffPattern, [1, 0]);
        if (length(humpStarts)>1)              
            needed{a}(1,1:length(next))=next(1,1:length(next));
            needed{a}(1,length(next)+1:(length(next)+humpStarts(1)))
            =x1(1,1:humpStarts(1));
            a=a+1;            
            needed{a}(1,1:(humpStarts(2)-humpStarts(1)))=x1(1,humpStarts(1)+1:humpStarts(2));
            a=a+1;
            next(1,1:length(x1)-humpStarts(2))=x1(1,humpStarts(2)+1:length(x1));
        elseif(length(humpStarts)==1)
            needed{a}(1,1:length(next))=next(1,1:length(next));
            needed{a}(1,length(next)+1:(length(next)+humpStarts(1)))
            =x1(1,1:humpStarts(1));
            a=a+1;             
            next(1,1:length(x1)-(humpStarts(1)))
               =x1(1,humpStarts(1)+1:length(x1)); 
        else 
            next(1,1:length(x1))=x1(1,1:length(x1));   
        end;  
   end;
end;
   %--for plotting the divided signals in the needed cell array---%
e=1; 
for t=1:1:length(needed)
for k=1:1:length(needed{t})
    r(1,e)=needed{t}(1,k);
    e=e+1;
end;
end;
plot(y);hold on;plot(r,'-r');

It is working fine except the last divided signal as shown here

I tried to figure out the problem but was not succeded.

can you try to help me out in finding the problem of why the last signal divided is not perfect which should contain the values from start of one hump to start of next humpwith but it is not.