How can i create a loop to generate daily averages from a csv. file for over four years and whose data was input at a 15minutes interval?

the data looks like this

Answer 1

[Cris LaPierre]

Use groupsummary and group the data by 'monthofyear' and 'dayofmonth' and the method set to mean. See this answer:

https://www.mathworks.com/matlabcentral/answers/1785535-average-of-variables-in-timetable-belonging-to-the-same-day-over-several-years#answer_1033575

Here is a simple example

Date = [datetime(2016,6,4)+calyears(0:5)';datetime(2016,6,5)+calyears(0:5)'];
X = rand(size(Date));
Y = rand(size(Date));
Z = rand(size(Date));
tbl = table(Date,X,Y,Z)

tbl = 12×4 table
       Date           X          Y           Z   
    ___________    _______    ________    _______

    04-Jun-2016    0.56436     0.95061    0.63577
    04-Jun-2017    0.70903    0.050817    0.74741
    04-Jun-2018    0.57119     0.54743    0.12786
    04-Jun-2019     0.2342     0.21309    0.78041
    04-Jun-2020    0.91886       0.353    0.45837
    04-Jun-2021     0.3717     0.70704    0.72707
    05-Jun-2016    0.58379     0.70093    0.39723
    05-Jun-2017    0.41526     0.26787    0.13649
    05-Jun-2018    0.15754     0.93554    0.50168
    05-Jun-2019    0.69327     0.69517    0.38602
    05-Jun-2020    0.93947     0.75884    0.64675
    05-Jun-2021    0.26944     0.37348    0.22696

out = groupsummary(tbl,["Date","Date"],["monthofyear","dayofmonth"],'mean')

out = 2×6 table
    monthofyear_Date    dayofmonth_Date    GroupCount    mean_X     mean_Y     mean_Z 
    ________________    _______________    __________    _______    _______    _______

           6                   4               6         0.56156    0.47033    0.57948
           6                   5               6          0.5098    0.62197    0.38252

[CKJ]

Thanks for the support. can you please give me some light about the error which i get when i try to apply the code on my data.

SLRdata=readtable("Gulu.csv","VariableNamingRule","preserve");

SLRdata.Date=datestr(SLRdata.Date,"local");

Tbl=table(SLRdata(:,"Date"),SLRdata(:,"Temperature (°C)"),SLRdata(:,"Relative Humidity (% RH)"),SLRdata(:,"Global Radiation (W/m²)"))

out = groupsummary(Tbl,["Var2","Var3","Var4"],["monthofyear","dayofmonth"],'mean')

[CKJ]

I was able to corrrect the error by critically analysing the help you had rendered in the first reply. THANKS very # I did not know group summary does the task very well.