# Finding daily min and max values for time series data

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Sunshine Seventy on 6 Sep 2022
Edited: Cris LaPierre on 6 Sep 2022
I have a time series of data at 15 minute time intervals across a 400 day period. I am trying to extract the maximum and minimum from one column of data for each day, and then calculating the difference. I can get the maximum or minumum for each day but am unsure of how to get all of the maximim and minimum values for the entire dataset.

Cris LaPierre on 6 Sep 2022
Edited: Cris LaPierre on 6 Sep 2022
Use groupsummary and group the data by 'day' and the method set to max and min.
Date = datetime(2016,6,4)+minutes(0:15:3000)';
X = rand(size(Date));
Y = rand(size(Date));
Z = rand(size(Date));
tbl = table(Date,X,Y,Z)
tbl = 201×4 table
Date X Y Z ____________________ ________ ________ ________ 04-Jun-2016 00:00:00 0.3386 0.043382 0.12585 04-Jun-2016 00:15:00 0.83698 0.42607 0.26318 04-Jun-2016 00:30:00 0.12522 0.4916 0.39504 04-Jun-2016 00:45:00 0.78164 0.42306 0.96615 04-Jun-2016 01:00:00 0.67576 0.22364 0.97667 04-Jun-2016 01:15:00 0.78426 0.68923 0.16458 04-Jun-2016 01:30:00 0.3168 0.3851 0.017321 04-Jun-2016 01:45:00 0.037264 0.12319 0.26101 04-Jun-2016 02:00:00 0.69026 0.71599 0.15885 04-Jun-2016 02:15:00 0.96935 0.16094 0.65121 04-Jun-2016 02:30:00 0.93266 0.62442 0.54567 04-Jun-2016 02:45:00 0.41745 0.83331 0.52272 04-Jun-2016 03:00:00 0.5479 0.6173 0.17108 04-Jun-2016 03:15:00 0.11542 0.85308 0.90392 04-Jun-2016 03:30:00 0.070657 0.38709 0.57379 04-Jun-2016 03:45:00 0.80039 0.32129 0.62989
out = groupsummary(tbl,"Date","day",["max","min"],"Z")
out = 3×4 table
day_Date GroupCount max_Z min_Z ___________ __________ _______ _________ 04-Jun-2016 96 0.97667 0.0016671 05-Jun-2016 96 0.98072 0.0024092 06-Jun-2016 9 0.81088 0.067344
out.Diff = out.max_Z-out.min_Z
out = 3×5 table
day_Date GroupCount max_Z min_Z Diff ___________ __________ _______ _________ _______ 04-Jun-2016 96 0.97667 0.0016671 0.975 05-Jun-2016 96 0.98072 0.0024092 0.97831 06-Jun-2016 9 0.81088 0.067344 0.74354