MATLAB: Getting max and min values in a day for data for 8 months

dataexcelMATLABmatrixmax-min values

I have data about dissolved oxygen concentration at every half an hour and I wish to calculate the max and minimum values during the day. The data is for about 8 months. Further, I wish to know the time at which I got the maximum values. I am assuming it should be a for loop, however, I am not so sure how to go about it. Any help would be appreciated.

Best Answer

There are plenty of ways of doing this which does not require loops.
If you did not require the index of the max, the simplest would be to use the retime method of a timetable object:
loggeddata = readtable('sample.csv');  %load the data

loggeddata.Properties.VariableNames = {'AcquisitionTime', 'OxygenConcentration'};  %optional but neater

loggeddata = table2timetable(loggeddata);  %convert to timetable
dailymax = retime(loggeddata, 'daily', 'max');  %get the daily max. Nothing more needed!
If you want the index of the max, then discretize and splitapply are probably the best tools. You don't need to convert to a timetable (you may still want to) for that:
loggeddata = readtable('sample.csv');  %load the data
loggeddata.Properties.VariableNames = {'AcquisitionTime', 'OxygenConcentration'};  %optional but neater
loggeddata = table2timetable(loggeddata);  %optional, convert to timetable
[group, date] = discretize(loggeddata.AcquisitionTime, 'day');  %watch out that date has one more element than max(group) (the end of the last bin)
[maxconc, row] = splitapply(@max, loggeddata, group);
dailymax = timetable(maxconc, loggeddata.AcquisitionTime(row), 'RowTimes', date(1:end-1), 'VariableName', {'MaxConcentration', 'ActualTime'})
Related Question