Interpolation of nan values

Question

Nicole Scerri 2015-5-25

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https://ww2.mathworks.cn/matlabcentral/answers/218508-interpolation-of-nan-values

回答： Walter Roberson 2015-5-25

I have a column with some Nans, and I'd like to interpolate the data to put numbers instead of the missing values.

The nans are in column 2.

Column 3 is the flag, so I'm looking for values that are number 4(flagged as missing/nan) and changing them to a 1(flagged as changed interpolated data), after the change is done.

This is what I tried:

numRows = size(database,1);
    for i=1:numRows
       if database(i,3) == 4;
        database(i,2) = interp1(database(i,2),'linear')
        database(i,3) = 1;
       end

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Stephen23 2015-5-25

编辑：Stephen23 2015-5-25

Do not use i or j for variable names, as these are both names of the inbuilt imaginary unit.

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Answer 1

Stephen23 2015-5-25

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/218508-interpolation-of-nan-values#answer_180313

编辑：Stephen23 2015-5-25

在 MATLAB Online 中打开

Here is an example of how to achieve something like what you need:

>> B(:,2) = [1,2,NaN,4,NaN,6,7,NaN,9];
>> B(:,3) = [0,0,  4,0,  4,0 0,  4,0]
B =
   1     0
   2     0
 NaN     4
   4     0
 NaN     4
   6     0
   7     0
 NaN     4
   9     0
>> idx = B(:,3)==4;
>> B(idx,2) = interp1(find(~idx), B(~idx,2), find(idx));
>> B(idx,3) = 1
B =
   1     0
   2     0
   3     1
   4     0
   5     1
   6     0
   7     0
   8     1
   9     0

Note that this completely avoids using any loop at all (i.e. fully vectorized code), and that it uses a syntax that taken from the interp documentation.