Calculate difference between datasets (timetables) with uneven size

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Renan Deuter 2022-7-20

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评论： Siddharth Bhutiya 2022-7-22

timetable.mat

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Hello,

I have two timetables timetableA and timetableB from two different sensors. One sensor does record data (here: Height) every second, while the other records in milliseconds. Therefore they don't have the same length.

Now I want to calculate the difference (for each second) between these two heights. The easist idea would be to just use

diff = timetableA.Height - timetableB.Height

However, they don't have the same length, so this doesn't work.

The next idea, was using intersect.

[sharedvals,idA, idB] = intersect(timetableA.Time,timetableB.Time,'stable');

However, the sensors aren't synchronized so most of the time, their timestamps don't intersect.

For example:

Sensor A:

timetableA.Time = [12:41:34.33 12:41:34:56 12:41:34:99 12:41:35:03 ....]
timetableB.Time = [12:41:35:00 12:41:36:00] 

So while 12:41:34:99 would be a very close match, the function can of course not find it.

Next I tried

>> TT = synchronize(timetableA, timetableB)

but I got the error:

"Target time vector for synchronization must be sorted (increasing or decreasing) and cannot contain missing times."

(Both tables are sorted and don't have NaT)

Is there a better way to compare the differences between the data?

Best Regards,

Renan

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Siddharth Bhutiya 2022-7-22

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The error message is correct timetableA contains one NaT row.

>> find(ismissing(timetableA.DateTime))
ans =
        1086
>> timetableA(1086,:)
ans =
  timetable
    DateTime    Heigth
    ________    ______
    NaT         595.36

Once you fix that you should be able to sychronize the two timetable, however, you would need to figure out how you want to line up the values to ensure that you get the correct difference. I would suggest going through the documentation of synchronize (link here) to figure out what time vector you want in the output timetable and how you want to resample the height values.

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