MATLAB: How to subtract mean daily values from hourly data

daily datahourly dataif thenmatrix dimensions

So I have flow data in an hourly time period, I was able to calculate the daily mean flow of these hourly values. Now I want to subtract the hourly flow values from the daily flow values to see how much change there is from the mean on a hourly basis.
Here is what I have so far:
Dates=datevec(DateandTime);
% Group by day
[unDates, ~, subs] = unique(Dates(:,1:3),'rows');
% Accumulate by day
AVG=[unDates accumarray(subs, Flow, [], @mean)];
f=AVG(:,4);
t=datenum(AVG(:,1:3));
figure
plot (x,y,t,f,'r')
legend('Hourly Flow','Daily Flow','location','best');
datetick ('x', 'mm-dd-yy', 'keepticks')
xlabel('Time');
ylabel('Flow [cfs]');
title('Daily Flow');
% axis tight
%%Difference from average flow
figure
n=datenum(AVG(:,1:3));
if n~=x
  DeltaFlow=Flow-AVG(:,4);
end
I keep getting an error matrix do not agree.

Best Answer

So, based on what you've done so far here is a spiffied up version:
%%generate sample data.
dateN = datenum('03-Sep-2014 15:26:10');
total15minsamps = 4*24*4; %4 days * 24 hours* 4 (15 min sec).
DATA = zeros(total15minsamps,7);
for ind = 1:total15minsamps %sample every 15 min.  
    data= 10+5*sin(2*pi/12*ind);    
    dateN = addtodate(dateN,15,'minute');
    Dvect = datevec(dateN);
    DATA(ind,:) = [Dvect data];
end
%%parse data
Dates = DATA(:,1:6);
Flow = DATA(:,end);
QuarterH_Time = datenum(DATA(:,1:end-1));
%%get hour's average flow
[unDates, HourSep, subs] = unique(Dates(:,1:4),'rows');
% Accumulate by hour
Hour_Data=[unDates accumarray(subs, Flow, [], @mean)];
Hour_AVG_flow=Hour_Data(:,5);
Hour_Time=datenum([Hour_Data(:,1:4) zeros(length(Hour_Data),2)]);
%%get day's average flow
[unDates, DaySep, subs] = unique(Dates(:,1:3),'rows');
% Accumulate by day
Day_Data=[unDates accumarray(subs, Flow, [], @mean)];
Day_AVG_flow=Day_Data(:,4);
Day_Time=datenum(Day_Data(:,1:3));
Day_Time = Day_Time + QuarterH_Time(1)-Day_Time(1); %offset so we don't start at the begining of the day
%%build subtraction matrix
DaySep = [DaySep;length(Flow)+1];
DeltaFlow = zeros(size(Flow));
for ind =1:length(DaySep)-1
    POI = DaySep(ind):DaySep(ind+1)-1;
    DeltaFlow(POI)=Flow(POI)-Day_AVG_flow(ind);
end
%%lets plot stuff
figure,plot(Hour_Time,Hour_AVG_flow,Day_Time,Day_AVG_flow,QuarterH_Time,DeltaFlow);
legend('Hourly Flow','Daily Flow','15 min data - day average','location','best');
datetick ('x', 'mm-dd-yy', 'keepticks')
xlabel('Time');
ylabel('Flow [cfs]');
title('Daily Flow');
Basically most of the stuff you can ignore because i needed to do some extra stuff to generate dummy data. But keep close attention to what i was doing with the DaySep array. Since we have two different length arrays that are based on the data i needed to use this value that is given by the unique() function to determine which indexes were deleted. With that i now know which 15 min data points correspond to which day.
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