Plot segments of an array with NaN using a for loop

Question

Jose Rego Terol 2021-3-2

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评论： Jose Rego Terol 2021-3-7

Hi,

I got an array with NaN. I want to plot, step-by-step, those segments of integers, that exceed a threshold and flanked by NaN, using a for loop.

Example:

Threshold=5
A=[NaN 1 2 3 4 4 3 1 NaN 2 4 5 10 11 12 14 13 11 7 5 3 NaN 2 3 7 15 20 25 17 13 9 5 1 NaN]

So, I want the loop to take the second segment of the integers flanked by NaN (2 - 3) and plot them. Then, I will do some operations with the plot, and I will continue with the loop using a wait(X) for the third segmentt (2 - 1).

The array always starts with a NaN, and finishes with an NaN.

for i = 1:length(A)
%     code for getting the plot and make the operation
wait(next_plot)
end

At least, if I can plot the second and the third segment together skipping the first one, I would save my day.

Best,

Jose

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Answer 1

dpb 2021-3-2

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编辑：dpb 2021-3-2

在 MATLAB Online 中打开

Rough outline to accomplish --

ix=find(isnan(A)); ix=ix(2:end);        % find the NaN sections, ignore first
for i=1:numel(ix)-1                     % over the groups
  subplot(2,1,i);                       % just to show the separate pieces;
  x=ix(i):ix(i+1);                      % set the x values to match
  B=A(x);                               % select the portion wanted from A this group
  B(B<=Threshold)=nan;                  % don't plot those <= Threshold
  plot(x,B,'*-')                        % plot verus original ordinal position
end

If only want the values above the threshold, then delete those below (or select only those above) instead and the corresponding x values to match.

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Jose Rego Terol 2021-3-7

在 MATLAB Online 中打开

Many thanks for your comment.

I am using the first lines of the code

ix=find(isnan(A)); ix=ix(2:end);        % find the NaN sections, ignore first
for i=1:numel(ix)-1

However, I am changing the rest because the rest of the code did not work for my code. I am usign ginput for each plot, therefore I cannot use subplots.

So, now I am doing like this but I got a problem to skip those segments that have lower values than the threshold (15)

ix=find(isnan(Trial(:,2))); ix=ix(1:end);        % find the NaN sections, ignore first
 for i=1:numel(ix)-1                    % numel(ix)-1 over the groups
  
  f=find(Trial((ix(1):ix(1+1)),2)>15); %Find all the values that are higher than 15 within this segment
  %%% Here I want to set the criteria: If f is empty, disp no spike found, and if f
  %%% has values, plot the entire segment (Trial)
  f=logical(f);
  if f == 0
      disp('no spike')
  else
      
      plot(Trial((ix(3):ix(3+1)),1),Trial((ix(3):ix(3+1)),2))
  end
pause()
%   plot(i);                       % just to show the separate pieces;
  
%   pause()
%   x=ix(i):ix(i+1);                      % set the x values to match
%   B=p(x);                               % select the portion wanted from A this group
%   B(B<=Threshold)=nan;                  % don't plot those <= Threshold
%   plot(x,B,'*-')                        % plot verus original ordinal position
end

The problem lies on the variable f. When the values are lower that 15, f is empty. Actually, I am looking for a code to say: in this segment or itineration, matlabdid not found values higher than 15. Then disp 'no spikes# and contiunue with the next segment.

Jose Rego Terol 2021-3-7

在 MATLAB Online 中打开

Well, I got a workaround with numel()

for i=1:numel(ix)-1                    % numel(ix)-1 over the groups
  
   f=numel(find(Trial((ix(i):ix(i+1)),2)>15));
    
   if f == 0
       disp('no spike')
   else
       
       plot(Trial((ix(i):ix(i+1)),1),Trial((ix(i):ix(i+1)),2))
   end
 pause()
%    plot(i);                       % just to show the separate pieces;
  
%    pause()
%   x=ix(i):ix(i+1);                      % set the x values to match
%   B=Trial(x,2);                               % select the portion wanted from A this group
%   B(B<=Threshold)=nan;                  % don't plot those <= Threshold
%   plot(x,B)                        % plot verus original ordinal position
end