observations every 8 or 9 weeks-interpolation

I have the cell matrix

 A={

 '28/12/08'    [2.3187]    [1.1517]
    '01/03/09'    [2.2314]    [1.1540]
    '03/05/09'    [2.2094]    [1.1702]
    '28/06/09'    [2.2666]    [1.1762]
    '30/08/09'    [2.2240]    [1.1860]
    '01/11/09'    [2.2387]    [1.1741]
    '03/01/10'    [2.3229]    [1.1729]
    '07/03/10'    [2.2253]    [1.1559]
    '09/05/10'    [2.2504]    [1.1678]
    '04/07/10'    [2.2673]    [1.1810]
    '05/09/10'    [2.1828]    [1.1816]
    '07/11/10'    [2.1271]    [1.1660]
    '02/01/11'    [2.3143]    [1.1674]
    '06/03/11'    [2.1860]    [1.1544]
    '08/05/11'    [2.1770]    [1.1704]
    '03/07/11'    [2.1832]    [1.1758]
    '04/09/11'    [2.1578]    [1.1766]
    '06/11/11'    [2.1612]    [1.1710]}

the observations represent a 8 or 9 week average. And I want to convert these values to estimated monthly averages via interpolation.My thought is the following

 %convert the mm/yy to number dates
 xi=datenum(A(:,1),'mm/yy')

 B=cell2mat(A(:,[2,3]));
for c = 2:3
B(:,c-1) = interp1(xi(1:2:end),cell2mat(A(:,c)),xi);
end

But I have the feeling that my approach is not correct. Any suggestions?

thank you in advance

[Azzi Abdelmalek]

it's not clear

[salva]

could you please be more specific?

thanks

Answer 1

[Andrei Bobrov]

One way:

d1 = datenum(A(:,1),'dd/mm/yy');
[y,m,d] = datevec(d1(1));
d2 = datenum(y,m,d+ (0:diff(datenum(A([1,end],1),'dd/mm/yy')))');
v = arrayfun(@(x)interp1(d1,cell2mat(A(:,x)),d2),2:size(A,2),'un',0);
[a,b] = datevec(d2);
[a1,b1,c] = unique([a,b],'rows');
[x,y] = ndgrid(c,1:size(A,2)-1);
out1 = accumarray([x(:),y(:)], cat(1,v{:}),[],@(x){mean(x)});
out = [cellstr(datestr(d2(b1),'mm/yy')),out1];

second way:

d1 = datenum(A(:,1),'dd/mm/yy');
[y,m,d] = datevec(d1([1,end]));
d3 = datenum(y(1),m(1)+(1:diff([y,m])*[12;1]+1)',1)-1;
out = [cellstr(datestr(d3,'mm/yy')), cell(numel(d3),size(A,2)-1)];
for j1 = 2:size(out,2)
    out(:,j1) = num2cell(interp1(d1,cell2mat(A(:,j1)),d3,'linear','extrap'));
end

etc.

Answer 2

[Walter Roberson]

Note that cell2mat(A(:,c)) is going to be the same as B(:,c-1)

You need to have another look at how many x and y values you are passing into interp1()

[salva]

could you please be more specific?

thanks

[Walter Roberson]

xi(1:2:end) is half the length of cell2mat(A(:,c)) but interp1() requires the first two arguments to be the same length.