Average values from timeseries

Question

Kate Heisenberg 2020-2-19

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回答： Jancoba Dorley 2022-2-28

Hiiii. I am very new to matlab. I have a timeseries of data that I would like to average for average values per hour per day per month per year ( 24*365=8760 values in output file). Basically the data is structured as follows:

Date Time Temperature

1/1/2005 1:00 282.19

1/1/2005 2:00 281.5

1/1/2005 3:00 281.04

1/1/2005 4:00 282.58

....

31/12/2014 23:00 294.75

31/12/2014 24:00 294.57

The data I am trying to import as individual vectors/columns or as a timetable. I would like to get a new table/matrix with 8760 new rows each averaging value of each hour of each day of each month by averaging all the 14 years of data. I have tried doing it using index or 'find' approach but it didnt quite work. Any help would be highly appreciated. Thaaanks :D

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Adam Danz 2020-2-19

Read your data in as a timetable if you haven't already done so.

Then use TT2 = retime(TT,'hourly','mean') to compute the hourly mean, monthly mean, yearly, etc.

https://www.mathworks.com/help/matlab/ref/timetable.retime.html#bvdhiwr-newTimeStep

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Answer 1

Adam Danz 2020-2-19

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编辑：Adam Danz 2020-2-19

Below is a general scetch of what you need to do. Give it a shot and if you get stuck, share the code and let us know where you're stuck.

Use d = day(t,'dayofyear') to get the day-of-year number for each datatime value where t is the datetime column.
Use h = hour(t) to get the hour of each datetime value where t is the datetime column.
Use [G,ID] = findgroups(d,h) to group the days & hours (d and h are from the steps above)
Use Y = splitapply(@mean,data,G) to get the mean of each group of data where 'data' is a colum in your table. G is from the previous step.

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Adam Danz 2020-2-20

编辑：Adam Danz 2020-2-20

Some feedback:

1) Just FYI; you can save several variables to the same mat file using :

save('data.mat', 'Date','Temp','Time')

2) You need to add a 3rd output to findgroup() so you can get the group ID for the day and the hour column (see code below).

Run this code and then inspect the table.

load('Date.mat')
load('Temp.mat')
load('Time.mat')
Day = day(Date,'dayofyear');
Hour = hour(UTtime);
[G,dayID,hourID]=findgroups(Day,Hour);  % Added 3rd output
Y = splitapply(@mean,Temperature,G);
% View the results in a table
T = table(Y, dayID, hourID, 'VariableNames', {'Means','DayOfYear','Hour'});
T(1:50,:)

Here's a way to confirm the results. In the first two lines below select a day-of-the-year and an hour.

The 3rd line manually computes the mean and the 4th line looks up the value in the table. They should (and do) match.

% Select day of year and hour
selectDayOfYear = 150; 
selectHour = 12; 
% manually compute the mean
testValue = mean(Temperature(Day == selectDayOfYear & Hour == selectHour))
% look up the mean in the table
T(T.DayOfYear == selectDayOfYear & T.Hour == selectHour, :)

We can see they match

>> testValue =
       310.97
>> T(T.DayOfYear == selectDayOfYear & T.Hour == selectHour, :) =
  1×3 table
    Means     DayOfYear    Hour
    ______    _________    ____
    310.97       150        12 