Hi Muhannad,
You have made a good start, you have a list of all unique dates in your unqdate. One thing I would recommend is to convert your date strings into serial date numbers, because it makes it much easier (in my opinion, anyway) to use logical indexing later on. You do this by saying
date_nums=datenum(date,'dd/mm/yyyy');
unqdate=unique(date_nums);
After this, you want to have a loop that executes the number of times corresponding to the size of your unqdate variable:
for i=1:size(unqdate,1)
Now you can use logical indexing to solve your problem. Its a little twisty but bear with me: you want to take from U_sold those indexes for which it is true that your full date vector matches the i'th entry in the unique date vector. And then sum the values from those indexes.
sales(i)=sum(U_sold(date_nums==unqdate(i)));
realdate{i}=datestr(unqdate(i),'dd/mm/yyyy') %and convert your unique date number back to a date string again
end
Logical indexing is a bit hairy when you first look at it, but think of it this way; you formulate a true/false statement, and only select the indexes for which the statement is true. An illustrative example:
A=[1 2 3 4 5 1 1];
%first, look at
A==1
%gives this: 1 0 0 0 0 1 1
%Which means if you ask for
A(A==1)
%you get simply 1 1 1 because it only takes the values out, for which we
%got a logical 1 before.
%We are essentially doing the same thing in your problem, but for unique dates
