MATLAB: How to compute the frequency of hourly/daily observation

for looptimedate

Hi everyone,

I want to compuet the hourly/daily number of observations. My data consistes of six colums (YYYY MM DD HH MM SS). Each date-time entry show one observation.

The measurements are uneven i.e. 0 to 100 etc. From the data set presnted below: I am interested to calcualet the hourly observations from 2015-05-06-10-35-00 to 2015-05-08-22-35-00 and same for the daily observations. (data also attached in excel sheet).

Thank you!

Best Answer

Your spreadsheet is empty.

I would load the data using readtable.

I would then create a new column and use datetime to convert YYYY MM DD HH MM SS to a datetime.

I would then use groupsummary to calculate a summary using 'hour' or 'day' as my grouping method.

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MATLAB: Average values after every n coloumns

I think something like this would be a pretty straightforward way to do what you want:

[N_loc,N_obs] = size(C);
N_obs_avg = 2920;
obs_idx = (0:9)*N_obs_avg;
C_avg = zeros(N_loc,N_obs_avg);
for i = 1:N_obs_avg
    C_avg(:,i) = mean(C(:,i+obs_idx),2);
end

Note that this method ignores the last 25 columns of C, since you stated the first tri-hourly time-step should only go up to column 26281 (rather than column 29201). If you want to include all the data (i.e., even those tri-hourly time-steps which actually have 11 years of data - the first 25), you could do this:

[N_loc,N_obs] = size(C);
N_obs_avg = 2920;
C_avg = zeros(N_loc,N_obs_avg);
for i = 1:N_obs_avg
    C_avg(:,i) = mean(C(:,i:N_obs_avg:end),2);
end

MATLAB: Create a single average day out of hourly data (33days)

"First row is date second is hourly mean temp."

That would be column, not row, as just a nit.

Yes, either groupsummary or varfun will do the job, but you need to create the grouping variable to use them...beginning with a timetable, tt that looks like the above, then

>> tt.Day=day(tt.Date);
>> varfun(@mean,tt,'groupingvariables','Day')
ans =
  2×3 timetable
            Date            Day    GroupCount    mean_Temp
    ____________________    ___    __________    _________
    07-Mar-2019 11:00:00     7         13         15.692  
    08-Mar-2019 00:00:00     8          8           13.5  
>> groupsummary(tt,'Day','mean')
ans =
  2×3 table
    Day    GroupCount    mean_Temp
    ___    __________    _________
     7         13         15.692  
     8          8           13.5  
>> [g,ig]=findgroups(tt.Day);
>> splitapply(@mean,tt.Temp,g)
ans =
   15.6923
   13.5000
>> table(tt.Date(ig),splitapply(@mean,tt.Temp,g))
ans =
  2×2 table
            Var1             Var2 
    ____________________    ______
    07-Mar-2019 17:00:00    15.692
    07-Mar-2019 18:00:00      13.5
>>

are various routes to the end...

>> retime(timetable(tt.Date(ig),splitapply(@mean,tt.Temp,g),'VariableNames',{'MeanTemp'}),'daily','nearest')
ans =
  2×1 timetable
            Time            MeanTemp
    ____________________    ________
    07-Mar-2019 00:00:00     15.692 
    08-Mar-2019 00:00:00       13.5 
>>

also gets rid of the odd beginning hour for each day if your data aren't all collected beginning at 00:00 each day.

You could add some error checking to ensure that don't include days that are just nightime or daytime measurements so those would bias results where there is some extreme from day to night.

ERRATUM:

Average over hours, not days as misread original intent:

tt.Hour=hour(tt.Time);
>> varfun(@mean,tt,"InputVariables",'Temp',"GroupingVariables",'Hour')
ans =
  21×3 timetable
            Time            Hour    GroupCount    mean_Temp
    ____________________    ____    __________    _________
    08-Mar-2019 00:00:00      0         1            16    
    08-Mar-2019 01:00:00      1         1            15    
    08-Mar-2019 02:00:00      2         1            13    
    08-Mar-2019 03:00:00      3         1            12    
    08-Mar-2019 04:00:00      4         1            16    
    08-Mar-2019 05:00:00      5         1            12    
    08-Mar-2019 06:00:00      6         1            12    
    08-Mar-2019 07:00:00      7         1            12    
    07-Mar-2019 11:00:00     11         1            16    
    07-Mar-2019 12:00:00     12         1            14    
    07-Mar-2019 13:00:00     13         1            12    
    07-Mar-2019 14:00:00     14         1            19    
    07-Mar-2019 15:00:00     15         1            23    
    07-Mar-2019 16:00:00     16         1            14    
    07-Mar-2019 17:00:00     17         1            15    
    07-Mar-2019 18:00:00     18         1            18    
    07-Mar-2019 19:00:00     19         1            17    
    07-Mar-2019 20:00:00     20         1            13    
    07-Mar-2019 21:00:00     21         1            14    
    07-Mar-2019 22:00:00     22         1            14    
    07-Mar-2019 23:00:00     23         1            15    
>>

Best Answer

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MATLAB: Average values after every n coloumns

MATLAB: Create a single average day out of hourly data (33days)

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