MATLAB: Seasonal average over years

average

I have monthly averages of daily data for 7 years (84×1). I would like to make an May-October average for the whole period (7×1). I have tried different approaches but I am just getting more confused.

Thank you!

Best Answer

Try this demo:

% Make sample data
temps = randi(100, 84, 1)
% Reshape to a month by year array.

tempsByMonth = reshape(temps, 12,7)
% Extract the May - October months.
mayThroughOct = tempsByMonth(5:10,:)
% Get the means over all those extracted months.
meanMayOct = mean(mayThroughOct(:))

Of course it could be make into a more cryptic, obtuse one liner if you wanted, but I went for understandability.

If you have the Image Processing Toolbox, you have mean2() so it can be shortened to

tempsByMonth = reshape(temps, 12,7) % Reshape to a month by year array.
meanMayOct = mean2(tempsByMonth(5:10,:)) % Get the means over extracted months.

and still be fairly readable.

Related Solutions

MATLAB: Daily average of several years data

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")

MATLAB: Dealing with leap years, creating arrays of yearly data

Here is an example using two years, one leap and one not. Should be easy for you to see how to generalize.

% Time series with one leap year and one not
T = rand(365+366,1);
% The years
Y = 1951:1952;
numberYears = numel(Y);
% Slick way to identify the leap years
isLeapYear = datenum(Y,2,29)~=datenum(Y,3,1);
T_new = nan(366,numberYears);
for ny = 1:numberYears
    numberDaysThisYear = 365+isLeapYear(ny);
    T_new(1:numberDaysThisYear,ny) = T(1:numberDaysThisYear);
    T(1:numberDaysThisYear) = []; % Deletes T as you go. Could do this differently
end

Best Answer

Related Solutions

MATLAB: Daily average of several years data

MATLAB: Dealing with leap years, creating arrays of yearly data

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