For command + interpolation: need some tips

Question

Charles Martineau 2012-6-7

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https://ww2.mathworks.cn/matlabcentral/answers/40523-for-command-interpolation-need-some-tips

I have a matrix "A" with three columns: daily dates,prices,and hours - all same size vector - there are multiple prices associated to hours in a day.

For each date, hours repeat and I need to interpolate linearly prices that I don't have for some "wanted" hours. But of course I can't use the command interp1 if my hours repeats in my column because I have multiple days. So say:

new_timeinhr = 0:0.25:max(A(:,3); %I want my hours in 0.25unit increments (like 9.5hrs);
day_hour = rem(new_timeinhour, 24);
new_timeinhr( day_hour <= 9.2 | day_hour >= 16.1 ) = []; %here I want only prices between 9.5hours and 16hours
%I then create a unique vectors of day and want to use a for and if command to interpolate "daily" and then stack my new prices in a vector one after the other%
days=unique(A(:,1));
    for j=1:length(days);
        if A(:,1)==days(j);
        int_prices(j) = interp1(A(:,2), A(:,3), new_timeinhr);
        end;
    end;

of course the error is now: In an assignment A(I) = B, the number of elements in B and I must be the same.

How can I write the int_prices(j) to stack?

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Answer 1

Charles Martineau 2012-6-7

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https://ww2.mathworks.cn/matlabcentral/answers/40523-for-command-interpolation-need-some-tips#answer_50200

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I think I solved it doing it this way:

new_timeinhr = 0:0.25:max(A(:,2));
day_hour = rem(new_timeinhr, 24);
new_timeinhr( day_hour <= 9.4 | day_hour >= 16.1 ) = [];
days=unique(data(:,1));
P=[];
for j=1:length(days);
    condition=A(:,1)==days(j);
    intprices = interp1(A(condition,2), A(condition,3), new_timeinhr);
    P=vertcat(P,intprices');
end;