Daily average of 8 years with data set every 3 hours

I have a data set consisting of 8 years from 2006-2013 of SST taken every 3 hours. There are some gaps in the data. I have already created a matrix 74*115*27192 (74 is the lon, 115 is the lat, and 27192 is the SST for all years. Now I have to calculate the daily mean. The Daily mean (Daily_mean) should generate a matrix of 74*115*X (X being the number of day). Instead it is generating a 74*115 matrix only. Any help. Thanks

clear all; close all;

fileList = dir('C:\Users\User\Desktop\Master Thesis\data\yearly\Rosario');

iniTime = datenum(1990, 1, 1, 0, 0, 0); 
cnt = 1;

fullSST = zeros (74,115,21792);
fullTime = zeros (2179,1);

for f = 1:numel(fileList);
    filename = fileList(f).name;
    [dirname name ext] = fileparts(filename);
    if (strcmp(ext, '.nc'))
        disp(['Processing file: ', filename]);

          info = ncinfo (filename);
          dataLon = ncread (filename, 'longitude'); %loading longitude data
          dataLat = ncread (filename, 'latitude'); %loading latitude data
          dataSST = ncread (filename, 'potemp'); %loading SST
          dataTime = ncread(filename, 'time'); 

          dataSST=squeeze(dataSST);
          for t = 1:1:size(dataSST, 3)

              SST = dataSST(:, :, t);
              Time = double(dataTime(t));

              currDate =  addtodate(iniTime, Time, 'hour');
              fullSST (:,:,cnt) = SST;
              fullTime (cnt) = currDate;
              cnt = cnt +1;
          end
      end
  end
%Full data set

startDate = datenum([2007 1 1 0 0 0]);
EndDate = datenum ([2013 12 31 0 0 0]);
currDate = startDate;
while (currDate <= EndDate)

      currDateVect = datevec(currDate);
      aDate = datenum([currDateVect(1) currDateVect(2) currDateVect(3) 0 0 0]);
      bDate = datenum([currDateVect(1) currDateVect(2) currDateVect(3) 23 59 59]);

      % find corresponding indices
      start_index = find(fullTime >= aDate);%find data > than the StartTime
      end_index = find(fullTime <= bDate); %find index of data ending in EndTime
      index = intersect(start_index, end_index);

      if (numel(index) > 0)
          Daily_mean = mean(fullSST(:, :, index), 3);

          Daily_time = currDate;
      end

      currDate = addtodate(currDate, 1, 'day');
  end

Answer 1

[Geoff Hayes]

MF - look closely at your code

 if (numel(index) > 0)
     Daily_mean = mean(fullSST(:, :, index), 3);
     Daily_time = currDate;
 end

You reset Daily_mean on each iteration of your while loop so you lose whatever it was initialized to previously and so when you program completes, you are left with the mean of the last day only.

If you know how many days there are, then you can pre-initialize this array as

 numDays = 42;
 Daily_mean = zeros(74,115,numDays);
 atDay = 1;
 while (currDate <= EndDate)
     % etc.
     if (numel(index) > 0)
         Daily_mean(:,:, atDay) = mean(fullSST(:, :, index), 3);
         Daily_time = currDate;
     end
     atDay = atDay + 1;
 end

Note how we use atDay to update Daily_mean. If you don't know the number of days, then you can do the same as above but just initialize Daily_mean as

 Daily_mean = [];

[MF]

Thank you very much

[Tanziha Mahjabin]

Hi, i want to plot a Hovmoller diagram or heatmap from satellite SST of several years. I have the data in daily average. I want to do weekly average. So i need to find every week (monday:sunday). How can i do that?

If tvec is the time (attached example data),

t=datetime(tvec)

d2 = dateshift(t,'dayofweek','monday') %this supposed to give each monday

But i am not sure how else am i supposed to that? Any help will be appreciated.

Answer 2

[Chad Greene]

A simpler solution might be downsample_ts.