A question regarding one of my previous questions

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salva 2012-8-14

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/46019-a-question-regarding-one-of-my-previous-questions

采纳的回答： Walter Roberson

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Dear all,

In my previous question

http://www.mathworks.de/matlabcentral/answers/44968-data-frequency-conversion-problem

I had

A = {

  '1-2 2004'      0.256       0.385
  '3-4 2004'      0.268      3.0394
  '5-6 2004'     0.0504      0.6475
  '7-8 2004'    14.0985    148.2583
  '9-10 2004'     0.1128      1.1506
  '11-12 2004'        NaN    148.2583
  '1-2 2005'        NaN    148.2583
  '3-4 2005'     2.5852     34.0146
  '5-6 2005'      0.322      3.2846
  '7-8 2005'    14.0985    148.2583
  '9-10 2005'     2.5852         NaN
  '11-12 2005'     0.2938       2.854
  '1-2 2004'      0.256       0.385
  '3-4 2004'      0.268      3.0394
  '5-6 2004'     0.0504      0.6475
  '7-8 2004'    14.0985    148.2583
  '9-10 2004'     0.1128      1.1506
  '11-12 2004'        NaN    148.2583
  '1-2 2005'        NaN    148.2583
  '3-4 2005'     2.5852     34.0146
  '5-6 2005'      0.322      3.2846
  '7-8 2005'    14.0985    148.2583
  '9-10 2005'     2.5852         NaN
  '11-12 2005'     0.2938       2.854
  '1-2 2004'      0.256       0.385
 '3-4 2004'      0.268      3.0394
  '5-6 2004'     0.0504      0.6475
  '7-8 2004'    14.0985    148.2583
  '9-10 2004'     0.1128      1.1506
  '11-12 2004'        NaN    148.2583
  '1-2 2005'        NaN    148.2583
  '3-4 2005'     2.5852     34.0146
  '5-6 2005'      0.322      3.2846
  '7-8 2005'    14.0985    148.2583
  '9-10 2005'     2.5852         NaN
  '11-12 2005'     0.2938       2.854}

These are bimonthly data and I wanted to obtain estimated monthly averages The solution that was given was

 data       = inpaint_nans(cell2mat(A(:,3:4)),2);
% Partition interpolation in blocks (first column)
blocks     = [A{:,1}];
unBlocks   = unique(blocks);
% Preallocate
interpData = cell(numel(unBlocks),1);
% Interpolate each block
for b = unBlocks
    idxBlock      = b == blocks;      % index the block
    n             = nnz(idxBlock)*2;  % counts its length
    interpData{b} = interp1((1:2:n)', data(idxBlock,:),(1:n-1)');
end

The only thing that I do not understand is why (1:n-1)' and not (1:n)'

thanks

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salva 2012-8-15

Will I be correct if i use (1:n)' instead of (1:n-1)'

thanks again

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Answer 1

Walter Roberson 2012-8-15

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/46019-a-question-regarding-one-of-my-previous-questions#answer_56287

在 MATLAB Online 中打开

The code is wrong, for the same reason that I pointed out in one of your previous Questions.

http://www.mathworks.com/help/techdoc/ref/interp1.html

If Y is a vector, it must have the same length as x

Your Y is not the same length as your x.

Whether you use (1:n-1) or (1:n) is not going to matter as the call is going to error out anyhow.

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salva 2012-8-15

I think that Y has the same length as x. In bith cases the size is 12 by 1

Walter Roberson 2012-8-15

In that csse, n-1 is correct. 1:2:n with n being even, ends at n-1 not at n. 1, 3, 5, 7... never even, so there is no input past 23 that would allow you to interpolate point 24 without using extrapolation.

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