MATLAB: How to caculate annual averge from daily data (i have just one column data for 15 years)

datasum

function [Ep,Pt,Qs] = moyenne_QEP( nomBassins,Bassins, yrMin, yrMax)
% Bassins: Structur with all Bassins
% nomBassins: Vector with bassins name
  d=0;
  for k =1:length(nomBassins)
    try 
      nomBassin=char(nomBassins(k));
      E = Bassins.(nomBassin).E;
      P = Bassins.(nomBassin).P;
      Q = Bassins.(nomBassin).QsMC;
      Ep = zeros(1,16);
      Pt = zeros(1,16);
      Qs = zeros(10,16);
      [~,C]=size(Q);
      csd = 0;
      sy  = 1;
      for yr = yrMin: yrMax         
        lpyr = (mod(yr,4)==0);
        dpy = csd + ones(size(yr))*365+lpyr;
        csd = cumsum(dpy);       
        sumE = 0;
        sumP = 0;
        for i= sy: dpy
          if(length(E)> i)
            sumE= sumE+ E(i);
          end
          if (length(P)> i)
            sumP= sumP+ P(i);
          end
          for j=1:C
            sumQ= 0;
            if (length(Q)> i)
              sumQ(j)= sumQ+ Q(i,j);
            end
          end
        end
        Pt(yr) = sumP/lpyr;
        Ep(yr) = sumE/lpyr;
        Qs(yr,:) = sumQ/lpyr;
        sy = csd;
      end
    catch
      d=d-1;
      warning(char(nomBassins(k)));
    end
  end

Best Answer

Simpler would be to create an indexing array of calendar years and then use accumarray to compute the means by the year.
dt=datetime(yrMin:yrMax,12,31)-datetime(yrMin,1,1);  % duration array of times wanted
iyr=calyears(dt)+1;                                  % number of year duration as index 1:N
mnP=accumarray(iyr,P,[],@mean);                      % mean over those years for var P
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