# calculate monthly averages of time series

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Richard on 5 Jul 2012
Commented: Benju Baniya on 12 Jul 2022
I have a dataset which contains measurements taken at discrete intervals for the past ~ 40 years. I would like to calculate the monthly mean values from the measurements. Consider the following example:
DateTime=datestr(datenum('1970-01-01','yyyy-mm-dd'):1:...
datenum('2011-12-31','yyyy-mm-dd'),...
'yyyy-mm-dd');
DateTime=cellstr(DateTime);
DateVec = datevec(DateTime);
dt = [1,4,32,232,101,44,23,1,87,843,456];
DateVec(dt,:) = [];
Data = rand(1,length(DateVec(:,1)));
Here, I have excluded some of the Dates in order to specify that the intervals of measurements were not continuous, obviously the measurements are far more spread out than shown above. So, what I would like to do is to use the date vector to specify each year and then calculate the mean of each month for a given year so that at the end I would have 12 measurements for each year.
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### Accepted Answer

Andrei Bobrov on 5 Jul 2012
Edited: Andrei Bobrov on 5 Jul 2012
[a,b,b] = unique(DateVec(:,1:2),'rows');
out = [a,accumarray(b,Data,[],@mean)]; %EDIT row
or
[a1,b1,b1] = unique(DateVec(:,1));
[a2,b2,b2] = unique(DateVec(:,2));
out = [nan,a2';a1,accumarray([b1,b2],Data,[],@mean)]; % EDIT row
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Benju Baniya on 12 Jul 2022
Hi, i am new to matlab and trying to work with timeseries data. What does a, b, b mean here? My data looks like as shown below. How do I calculate GPP based on month so that I get 12 values for each year? Thanks in advance.
YEAR TIMESTAMP DoY NEE GPP
2013 201301010030 1 -0.0064 0.0025
2013 201301010100 2 - 0.0076 0.0026
2014 201401010030 1 0.0983 -0.0076
2014 201301010100 2 0.0075 - 0.0089

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