Combine Tables with different record rate

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Richard Vergin 2018-7-22

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评论： Richard Vergin 2018-10-13

Hey Everybody,

I need to join two tables by the common Parameter "Time_secs_" which represents the record date of my sensor data. Unfortunately, in one table the record is 0.5 seconds while in the second it is 0.1 seconds. Therefore the second table has 481002 rows while the first only has 80167 rows.

Now I want to join them by their record rate and simply add blank cells for every signal from table 1 to the time_secs_0 0.1, 0.2, 0.25, 0.3, 0.4, 0.6, 0.7, 0.75, 0.8, 0.9 (some signals are also taken every 0.25 seconds, thats why 0.25 and 0.75 are included).

How can I do this? Is there any specification I can make to the "join"-function or will it not work with this at all?

Thanks a lot in advance!

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Richard Vergin 2018-7-24

For interested readers: after adding a Time-Column with similar values (thanks to Guillaume's solution) I was able to combine the tables. Outerjoin works for adapting the fine record rate, joing for adapting the small one.

Peter Perkins 2018-8-3

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Richard, you can do that (use tables and joins), but if you are using R2016b or later, you will be much happier using timetables and synchronize:

>> tt1 = timetable((1:10)','RowTimes',seconds(0:1:9))
tt1 =
  10×1 timetable
    Time     Var1
    _____    ____
    0 sec      1 
    1 sec      2 
    2 sec      3 
    3 sec      4 
    4 sec      5 
    5 sec      6 
    6 sec      7 
    7 sec      8 
    8 sec      9 
    9 sec     10 
>> tt2 = timetable((11:15)','RowTimes',seconds(0:2:8))
tt2 =
  5×1 timetable
    Time     Var1
    _____    ____
    0 sec     11 
    2 sec     12 
    4 sec     13 
    6 sec     14 
    8 sec     15 
>> synchronize(tt1,tt2)
ans =
  10×2 timetable
    Time     Var1_tt1    Var1_tt2
    _____    ________    ________
    0 sec        1          11   
    1 sec        2         NaN   
    2 sec        3          12   
    3 sec        4         NaN   
    4 sec        5          13   
    5 sec        6         NaN   
    6 sec        7          14   
    7 sec        8         NaN   
    8 sec        9          15   
    9 sec       10         NaN

But beware: .1 is not a nice floating point number. You may find that synchronize treats some times that look the same as different, because they are different. At that level of resolution, you are usually better off using the milliseconds function to construct time vectors than using the seconds function.

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Answer 1

Guillaume 2018-7-24

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How can I create an additional column within the table which contains all the information of those three others and makes a time out of this?

yourtable.newcolumnname = datetime([zeros(height(yourtable), 3), yourtable.hourcolumn, yourtable.minutecolumn, yourtable.secondcolumn], 'Format', 'HH:mm:ss')

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Richard Vergin 2018-10-13

编辑：Richard Vergin 2018-10-13

Hey, I'm on a similar problem now. I'm trying to create a datetime-column from 6 columns, including year, month and day now. I'm trying with the same logic that Guillaume proposed and wrote the following code:

Minus22_FlightParameter_Hydraulics_Uniform_Table.GMTDATETIME = datetime([zeros(height(Minus22_FlightParameter_Hydraulics_Uniform_Table),6),... Minus22_FlightParameter_Hydraulics_Uniform_Table.GMTYEAR, Minus22_FlightParameter_Hydraulics_Uniform_Table.GMTMONTH,... Minus22_FlightParameter_Hydraulics_Uniform_Table.GMTDAY, Minus22_FlightParameter_Hydraulics_Uniform_Table.GMTHOURS,... Minus22_FlightParameter_Hydraulics_Uniform_Table.GMTMINUTES, Minus22_FlightParameter_Hydraulics_Uniform_Table.GMTSECONDS], 'Format', 'yyyy:MM:dd:HH:mm:ss');

However I receive the following error message: Error using datetime (line 569) Numeric input data must be a matrix with three or six columns, or else three, six, or seven separate numeric arrays. You can also create datetimes from a single numeric array using the 'ConvertFrom' parameter.

I don't know how to fix it, since I am using 6 seperate numeric arrays. Do you know what I am doing wrong?

Best, Richard