MATLAB: Using timetable to sort and apply functions to data with a timestep greater than one year

arraydataexcelMATLAB and Simulink Student Suitetabletimesteptimetable

I am working with daily temperature data; min, max, and mean over a period of 40 years. I have no problem using the timetable functionality to sort the data, by year, month,etc, however I want to compare the data for the lifetime and find the standard deviation and median. I know this is possible to do using arrays and for loops to sort and group the data, but because I have it set-up with timetables already I think it would be more elegant? Using the retime function I could change the timestep, but getting the appropriate data from that didn't work.

Thanks!

Best Answer

If you mean that instead of regular time steps, e.g., monthly, yearly, etc. You want to use a custom time-step, you can use the following signature of retime() function

TT2 = retime(TT1,'regular',method,'TimeStep',dt)

here dt can be defined using duration().

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MATLAB: How to calculate Daily mean and monthly mean from hourly data

I would recommend the following steps:

Import the data file
Arrange the data and create timetable variable
Apply retime funciton to obtain daily/monthly average

The following is an example:

% Read the data file
opts = detectImportOptions('test_pog.txt');
T = readtable('test_pog.txt',opts);
% Make a datetime vector
Time = datetime(T{:,1},'InputFormat','yyyy.MM.dd.');
Time.Hour = T{:,2};
% Add the datetime vector and remove the 1st&2nd columns
T.Time = Time;
T(:,1:2) = [];
% Convert to timetable
TT = table2timetable(T);
% Apply retime function to obtain daily/monthly mean
TTdailyMean = retime(TT,'daily','mean');
TTmonthlyMean = retime(TT,'monthly','mean');

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")

Best Answer

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MATLAB: How to calculate Daily mean and monthly mean from hourly data

MATLAB: Daily average of several years data

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