A question regarding one of my previous questions

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salva
salva 2012-8-14
Dear all,
In my previous question
http://www.mathworks.de/matlabcentral/answers/44968-data-frequency-conversion-problem
I had
A = {
1 '1-2 2004' 0.256 0.385
1 '3-4 2004' 0.268 3.0394
1 '5-6 2004' 0.0504 0.6475
1 '7-8 2004' 14.0985 148.2583
1 '9-10 2004' 0.1128 1.1506
1 '11-12 2004' NaN 148.2583
1 '1-2 2005' NaN 148.2583
1 '3-4 2005' 2.5852 34.0146
1 '5-6 2005' 0.322 3.2846
1 '7-8 2005' 14.0985 148.2583
1 '9-10 2005' 2.5852 NaN
1 '11-12 2005' 0.2938 2.854
2 '1-2 2004' 0.256 0.385
2 '3-4 2004' 0.268 3.0394
2 '5-6 2004' 0.0504 0.6475
2 '7-8 2004' 14.0985 148.2583
2 '9-10 2004' 0.1128 1.1506
2 '11-12 2004' NaN 148.2583
2 '1-2 2005' NaN 148.2583
2 '3-4 2005' 2.5852 34.0146
2 '5-6 2005' 0.322 3.2846
2 '7-8 2005' 14.0985 148.2583
2 '9-10 2005' 2.5852 NaN
2 '11-12 2005' 0.2938 2.854
3 '1-2 2004' 0.256 0.385
3 '3-4 2004' 0.268 3.0394
3 '5-6 2004' 0.0504 0.6475
3 '7-8 2004' 14.0985 148.2583
3 '9-10 2004' 0.1128 1.1506
3 '11-12 2004' NaN 148.2583
3 '1-2 2005' NaN 148.2583
3 '3-4 2005' 2.5852 34.0146
3 '5-6 2005' 0.322 3.2846
3 '7-8 2005' 14.0985 148.2583
3 '9-10 2005' 2.5852 NaN
3 '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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采纳的回答

Walter Roberson
Walter Roberson 2012-8-15
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.
  2 个评论
salva
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
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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