Fill in missing NaNs

Question

Cuong Nguyen 2020-3-30

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/513936-fill-in-missing-nans

评论： Cuong Nguyen 2020-3-31

I am trying to fill these NaNs following this rule: If there is a single NAN, I want the NAN to be filled in with the average of the numbers before and after. If there is more than one NAN. I want the NAN to be filled in with the nearest number. For example, row 2305 should be the average of 16.3 and 14.8, from 2298 to 2304 should be 16.3, and from 2306 to 2312 should be 14.8.

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Cuong Nguyen 2020-3-30

在 MATLAB Online 中打开

L1 = length(maxTemp);
for i = 1:1:L1
    
    for j = 0:20
        if  i <27028 && isnan(maxTemp(i+j))
          a=j; 
        else
            break
        end
    end
    
    if isnan(maxTemp(i)) && isnan (maxTemp(i+a)) % 'a' distance away from i
       for k = 0:a % new variable which goes upto variable a
           f = a; %new variable which goes down from variable a
            
               if (a/2 > k) 
                   maxTemp(i+k)=maxTemp(i+k-1);
                   maxTemp(i+f)=maxTemp(i+f+1);
                   
               else
                   break
               end
              
                if mod(a,2)== 0 % if a is even
                   maxTemp(i+k)= avg(maxTemp(i+k-1),maxTemp(i+k+1));
                 
                elseif mod(a,2)~= 0 % if a is not even
                   maxTemp(i+k)=maxTemp(i+k-1);
                   maxTemp(i+f)=maxTemp(i+f+1);
                end
            f = f-1; % decrease by 1 
       
       end
    end
    end

That array is showing maximum temperature day by day (on the photo is day 2297 to day 2313). After I run my code, this is what I got:

I need row 2305 to be average of 16.3 and 14.8, and row 2298 - 2304 to be 16.3. Thanks a lot for your time.

Image Analyst 2020-3-30

Why not use interp1() or regionfill() to linearly interpolate from one side to the other?

Cuong Nguyen 2020-3-30

I am quite a newbie to matlab, can you make it more specific? Thanks.

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Answer 1

Ameer Hamza 2020-3-30

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/513936-fill-in-missing-nans#answer_422901

编辑：Ameer Hamza 2020-3-30

在 MATLAB Online 中打开

Try this:

x = [1;2;3;4;nan;nan;nan;nan;nan;5;7;8;nan;nan;nan;nan;11;11;12;nan;nan;nan;15];
bb = regionprops(isnan(x));
idx_nnan = find(~isnan(x));
idx_nan = find(isnan(x));
[~,idx] = min(abs(idx_nan - idx_nnan'), [], 2);
x(idx_nan) = x(idx_nnan(idx));
a = [bb.Centroid];
a(1:2:end) = [];
bb = bb(a==fix(a));
for i=1:numel(bb)
    idx_center = bb(i).Centroid(2);
    idx = cumsum(bb(i).BoundingBox([2 4])) + [-0.5 0.5];
    x(idx_center) = mean(x(idx));
end

Original x:

x =
     1
     2
     3
     4
   NaN
   NaN
   NaN
   NaN
   NaN
     5
     7
     8
   NaN
   NaN
   NaN
   NaN
    11
    11
    12
   NaN
   NaN
   NaN
    15  

New x:

x =
0000
0000
0000
0000
0000 % <--- nearesr value
0000 % <--- nearesr value
5000 % average
0000 % <--- nearesr value
0000 % <--- nearesr value
0000
0000
0000
0000 % <--- nearesr value
0000 % <--- nearesr value
0000 % <--- nearesr value 
0000 % <--- nearesr value
0000
0000
0000
0000 % <--- nearesr value
5000 % average
0000 % <--- nearesr value
0000

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Cuong Nguyen 2020-3-31

Oh nice nice. Thank you, I got something to learn from this!

Ameer Hamza 2020-3-31

Glad to be of help.

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Answer 2

darova 2020-3-30

1
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https://ww2.mathworks.cn/matlabcentral/answers/513936-fill-in-missing-nans#answer_422857

在 MATLAB Online 中打开

Use bwlabel

A1 = isnan(A);                              % find NaN
[L,n] = bwlabel(A1);                        % label each region
xx = 1:length(A);
for i = 1:n                                 % loop through each region
    BW = L==i;                              % select region
    if sum(BW(:))>1                         % if more than one 'NaN'
        ix1 = find(BW,1,'first');           % first index of region
        ix2 = floor(mean(BW.*xx));          % find mean index in region
        ix3 = find(B2,1,'last');            % last index of region
        A(ix1:ix2) = A(ix1-1);              % fill first part
        A(ix2+1:ix3) = A(ix3+1);            % fill second part
    else
        ix = find(BW);
        A(ix) = mean(A(ix([-1 1])));        % average
    end
end

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Cuong Nguyen 2020-3-31

I tried yours and I got this message "Array indices must be positive integers or logical values". It also shows that the error is in "A(ix) = mean(A(ix([-1 1])))" line.

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Answer 3

Andrei Bobrov 2020-3-31

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/513936-fill-in-missing-nans#answer_423039

在 MATLAB Online 中打开

This question is a repeat of this question:

x = [1;2;3;4;nan;nan;nan;nan;nan;5;7;8;nan;nan;nan;nan;11;11;12;nan;nan;nan;15];
out = [x,f1(x)]
x = [16.3;nan(15,1);14.8];
out = [x, f1(x)]

Here f1:

function out = f1(x)
    b1 = fillmissing(x,'linear');
    b2 = fillmissing(x,'nearest');
    d = [0;diff(bwdist(~isnan(x)),2);0]==-2;
    out = b2;
    out(d)  = b1(d);
end