Finding daily min and max values for time series data

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.

Answer 1

[Cris LaPierre]

Use groupsummary and group the data by 'day' and the method set to max and min.

See this answer: https://www.mathworks.com/matlabcentral/answers/1792775-how-can-i-create-a-loop-to-generate-daily-averages-from-a-csv-file-for-over-four-years-and-whose-d?s_tid=srchtitle

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