How to calculate an average value in a matrix with respect to timestamps

Question

Eivind Sommerstad 2023-4-10

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评论： Eivind Sommerstad 2023-4-13

Hello, i have a "mixed Rinex observation" file that i have read into matlab with the "rinexread()" function. What i want to do is "group" the "SIC" values by the "Time" values so that for example all the values for SIC in the timestamp 13:49:10 gets added together, averaged out and then saved to a new matrix. I want this to happen for every "new" timestamp going down this file. For clarification, this is for the GPS part of the observation file.

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Walter Roberson 2023-4-10

I recommend that you convert to timetable() objects and use retime()

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Answer 1

Vinayak Choyyan 2023-4-12

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Hi Eivind,

As per my understanding, you would like to sum ‘S1C’ data after grouping it by time.

Please check out the below example.

filename = "GODS00USA_R_20211750000_01H_30S_MO.rnx";
data = rinexread(filename);
tmp=data.GPS(:,9);
tmp=groupsummary(tmp,'Time','sum');
output=tmp(:,[1 3])
output = 120×2 table
Timesum_S1C___________________________

    24-Jun-2021 00:00:00       433 
    24-Jun-2021 00:00:30    431.75 
    24-Jun-2021 00:01:00    431.25 
    24-Jun-2021 00:01:30     436.5 
    24-Jun-2021 00:02:00     435.5 
    24-Jun-2021 00:02:30       433 
    24-Jun-2021 00:03:00    435.75 
    24-Jun-2021 00:03:30    432.25 
    24-Jun-2021 00:04:00     433.5 
    24-Jun-2021 00:04:30    435.75 
    24-Jun-2021 00:05:00    438.25 
    24-Jun-2021 00:05:30     436.5 
    24-Jun-2021 00:06:00    437.75 
    24-Jun-2021 00:06:30    437.75 
    24-Jun-2021 00:07:00    437.25 
    24-Jun-2021 00:07:30    435.25 

Since ‘data.GPS’ is of type ‘timetable’, we can use the ‘groupsummary’ function to find the sum of data after grouping it by column ‘Time’.

Note: In the above code, ‘S1C’ is the 9th column in ‘data.GPS’. The file "GODS00USA_R_20211750000_01H_30S_MO.rnx" is included with MATLAB and you can directly access it like I did in the above example.

For more details, please visit these documentation pages:

‘timetable’ https://www.mathworks.com/help/matlab/ref/timetable.html
‘groupsummary’ https://www.mathworks.com/help/matlab/ref/double.groupsummary.html
How to sum over grouped data in a table https://www.mathworks.com/matlabcentral/answers/447189-how-to-sum-over-grouped-data-in-a-table

I hope this helps resolve the issue you were facing.

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Eivind Sommerstad 2023-4-13

Thank you for your answer, after some time i managed to find a way to make it work on my own. Wether it is a good way or not im not so sure about but it works for what i need it to do.

Here is a part of the code i wrote. It just repeats for the other variables defined at the start.

At the very end of the script i plot the data.