How to convert consecutive numbers in NaN?

Question

Fabian Moreno 2021-5-12

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https://ww2.mathworks.cn/matlabcentral/answers/827895-how-to-convert-consecutive-numbers-in-nan

评论： Star Strider 2021-5-12

Hi there, I have a matrix (8760x18) with random numbers. the values have valid zeros and invalid zeros. The invalid zeros are continually presented, I mean postion (12 13 14 15 16 . . . 21) or any position between 1 and 8760. The valid zeros have randomly positions, I mean position (9 has zero value) but the position before and after are numbers > 0. To understand better I did an example, which is varaible (y). It has 10 continually invalid zeros that I would like become NaN, but it has also valid zeros that I would like to keep. My idea is the next -> If there is more than fice consecutive zeros, become NaN, if not, leave 0's.

|-- invalid zeros--| |valid|

y= [1 2 3 5 2 6 4 8 0 5 2 0 0 0 0 0 0 0 0 0 0 1 2 5 6 9 8 74 0 0 0 32 8 4 6 1 10 2]';

I already try to do the next code, but the result is:

for i=1:length(y)
    if y((i)+5,1)==0 & y((i)+4,1)==0 & y((i)+3,1)==0 & y((i)+2,1)==0 & y((i)+1,1)==0
        y(i,1) = NaN;
    end
end
y= [1 2 3 5 2 6 4 8 0 5 NaN NaN NaN NaN NaN NaN NaN 0 0 0 0 0 2 5 6 9 8 74 0 0 0 32 8 0 6 1 10 0];

And like the last number is zero, obviusly get an error that exceeds array bounds, but coudn't fix it.

Index in position 1 exceeds array bounds (must not exceed 38).

Error in analise_dados_mp25 (line 71)

if y((i)+5,1)==0 & y((i)+4,1)==0 & y((i)+3,1)==0 & y((i)+2,1)==0 & y((i)+1,1)==0

Thanks in advanced.

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Answer 1

Star Strider 2021-5-12

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https://ww2.mathworks.cn/matlabcentral/answers/827895-how-to-convert-consecutive-numbers-in-nan#answer_697740

在 MATLAB Online 中打开

Try this —

y = [1 2 3 5 2 6 4 8 0 5 2 0 0 0 0 0 0 0 0 0 0 1 2 5 6 9 8 74 0 0 0 32 8 4 6 1 10 2]';
y = [y;y;y; zeros(8,1)];                                        % Extend 'y'
y = 122×1
     1
     2
     3
     5
     2
     6
     4
     8
     0
     5
z5 = strfind(y(:)', [0 0 0 0 0]);                               % Start Indices Of Consecutive 'zero(1,5)'
dz5 = [1 find(diff(z5)>1)+1 numel(z5)];                         % Index Differences
for k = 1:numel(dz5)-1                                          % Do Replacements
    y(z5(dz5(k):dz5(k+1))-1) = NaN;
end
for k = 1:20:numel(y)                                           % Check Result
    row = sprintf([repmat('%d  ',1,20) '\n'],y(k:min(k+19,numel(y))))
end
row = 
    '1  2  3  5  2  6  4  8  0  5  NaN  NaN  NaN  NaN  NaN  NaN  0  0  0  0  
     '
row = 
    '0  1  2  5  6  9  8  74  0  0  0  32  8  4  6  1  10  2  1  2  
     '
row = 
    '3  5  2  6  4  8  0  5  NaN  NaN  NaN  NaN  NaN  NaN  0  0  0  0  0  1  
     '
row = 
    '2  5  6  9  8  74  0  0  0  32  8  4  6  1  10  2  1  2  3  5  
     '
row = 
    '2  6  4  8  0  5  NaN  NaN  NaN  NaN  NaN  NaN  0  0  0  0  0  1  2  5  
     '
row = 
    '6  9  8  74  0  0  0  32  8  4  6  1  10  NaN  NaN  NaN  NaN  0  0  0  
     '
row = '0  0  '

I made it as robust as I could.

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Star Strider 2021-5-12

在 MATLAB Online 中打开

I am now not certain what you want to do.

It may be necessary to experiment with my code to get the result you want, since I may not understand that correctly.

Try this modification —

y = [1 2 3 5 2 6 4 8 0 5 2 0 0 0 0 0 0 0 0 0 0 1 2 5 6 9 8 74 0 0 0 32 8 4 6 1 10 2]';
y = [y;y;y;zeros(8,1)];                                         % Extend 'y'
nz = find(y ~= 0);
if nz(1)>1
    nz = [1; nz];
elseif nz(end) ~= numel(y)
    nz = [nz; numel(y)+1];
end
dnz = find(diff(nz)>=5);
idx = [nz(dnz)+1 nz(dnz+1)-1];
for k = 1:size(idx,1)
    y(idx(k,1):idx(k,2)) = NaN;
end
for k = 1:20:numel(y)                                           % Check Result
    row = sprintf([repmat('%d  ',1,20) '\n'],y(k:min(k+19,numel(y))))
end
row = 
    '1  2  3  5  2  6  4  8  0  5  2  NaN  NaN  NaN  NaN  NaN  NaN  NaN  NaN  NaN  
     '
row = 
    'NaN  1  2  5  6  9  8  74  0  0  0  32  8  4  6  1  10  2  1  2  
     '
row = 
    '3  5  2  6  4  8  0  5  2  NaN  NaN  NaN  NaN  NaN  NaN  NaN  NaN  NaN  NaN  1  
     '
row = 
    '2  5  6  9  8  74  0  0  0  32  8  4  6  1  10  2  1  2  3  5  
     '
row = 
    '2  6  4  8  0  5  2  NaN  NaN  NaN  NaN  NaN  NaN  NaN  NaN  NaN  NaN  1  2  5  
     '
row = 
    '6  9  8  74  0  0  0  32  8  4  6  1  10  2  NaN  NaN  NaN  NaN  NaN  NaN  
     '
row = 'NaN  NaN  '

Here, all occurrences of five or more zeros in a row are NaN. Occurrences of less than five zeros in a row are not NaN.

Star Strider 2021-5-12

在 MATLAB Online 中打开

Thank you!

No worries! I will explain as best I can how it works.

The if block checks the starting and ending indices of ‘nz’ to be certain that all the elements of ‘y’ are accounted for in it. So if the first element of ‘nz’ is not 1, the if block concatenates a 1 to the beginning of it, in order to correct for any zeros at the beginning of the vector. If the last element is not the end of the vector, for the same reason, the if block concatenates that value to the end of it and increments it by 2 because the code later takes the differences in ‘nz’ to determine the correct indices for the NaN replacement. The if block is necessary for ‘dnz’ to produce accurate results.

The ‘dnz’ (‘differences in ‘nz’) assignment finds differences between the consecutive nonzero element indices that are greater than or equal to 5. This is to meet the design requirements.

The ‘idx’ matrix are the beginning and ending elements of the vector segments to be replaced by NaN. They are used in the for loop that follows it. It made it easier for me to troubleshoot the code. I could have omitted it and instead written the loop as:

for k = 1:size(idx,1)
    y(nz(dnz(k))+1:nz(dnz(k)+1)-1) = NaN;
end

with the same effect (I tested it to be certain). It was just easier to write the matrix and then refer to elements of it in the loop.

.

Fabian Moreno 2021-5-12

Thanks a lot, Star Strider! I got it much better. Amazing! Thank you.

Star Strider 2021-5-12

As always, my pleasure!

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