MATLAB: Daily average of several years data

averagedailydataseveralyears

Hi!
I have SST data from 1981-2019. I'd like to calculate the daily average for each day of the year.
So the value for each day is the average of the SST of the 39 years.
The structure of the data is like this:
sst_date=[day,month,year,sst];
I'm thinking about looping sst_date, but is very confusing because the months and some years have different days.
Is there any way easier?
Thank you

Best Answer

If you can turn your data into a table, use the groupsummary function. Assuming you want to average days from each year, you could do this:
dailyAvg = groupsummary(dataTbl,["monthVar","dayVar"],"mean","sst")
If you actually convert your date into a datetime variable, you could also do this:
groupsummary(dataTbl,"date","dayofyear","mean","sst")
Here's the full code using the snippet of data you provided above.
data = [1	1	1982	13.4691935954243
2	1	1982	13.4287935963273
3	1	1982	13.4183935965598
4	1	1982	13.9135935854912
5	1	1982	13.9483935847134
6	1	1982	13.9511935846508
7	1	1982	13.9471935847402
8	1	1982	14.0023935835064
9	1	1982	13.9711935842037
10	1	1982	13.8475935869664];
dataTbl = table(data);
dataTbl = splitvars(dataTbl,"data","NewVariableNames",["day","month","year","sst"])
% option one - group by month then day.
dailyAvg1 = groupsummary(dataTbl,["month","day"],"mean","sst")
% option two - use the groupbin "dayofyear" on datetime variable "date"
dataTbl.date = datetime(fliplr(data(:,1:3)));
dailyAvg2 = groupsummary(dataTbl,"date","dayofyear","mean","sst")
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