interpolation for irregural observations

Dear all,

I have

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'        0.322          148.2583
    1    '1-2 2005'        0.322         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         0.322      
    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'        0.322          148.2583
    2    '1-2 2005'        0.322        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         0.322      
    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'        0.322         148.2583
    3    '1-2 2005'        0.322          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         0.322      
    3    '11-12 2005'     0.2938       2.854}These data are bimonthly data.

The code

 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
transforms these bimonthly data to monthly.

The only problem is that with this approach assumes that every month has same length.

Is it possible to modify it so as to take into account that the months have different length?

thanks

[Walter Roberson]

Looks to me like you deleted your old (identical) question and reposted it. :-(

[salva]

correct!:)

Matlab is great and all of you as well!

Answer 1

[Sean de Wolski]

Convert the dates to date numbers ( doc datenum ) and then use them as the x values corresponding to your data.

[salva]

Hi Sean. I am a bit confused. You mean to convert the months to numbers using datemun. For instance

datenum('09/2001', 'mm/yyyy')=x and then

outqq = interp1(x,A(x,:),x);

Am I right?

cheers

[Sean de Wolski]

Yes. The date numbers will be a numerical representation of the days. So March 17th will be 12 different from March 29th which will be two different from March 31st. Then when you use interp1 the non-even spacing will be accounted for.