How to grab the first instance of a timestamp based on the second

Question

R 2022-6-14

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1739975-how-to-grab-the-first-instance-of-a-timestamp-based-on-the-second

评论： R 2022-6-14

采纳的回答： Peter Perkins

Hello everyone.

I was having some trouble figuring out how I could filter out rows of data when we have a high frequency data sample.

Ex:

As you can see in the image, this is a tall table and it consists of multiple timestamps but with varying milliseconds. I want to be able to grab the first instance of the rows where the timestamp based on the seconds is unique. So 14-06-2022-15:30:19.6175... then 14-06-2022-15:30:20.042563... then 14-06-2022-15:30:21.00559

Thank you for your help!

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Answer 1

Peter Perkins 2022-6-14

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1739975-how-to-grab-the-first-instance-of-a-timestamp-based-on-the-second#answer_985480

It's a one-liner using a timetable and retime, with NewTimeStep 'secondly' and Method 'firstValue':

>> tt = timetable(rand(10,1),RowTimes=datetime("now",Format="dd-MMM-uuuu HH:mm:ss.SSS")+seconds(3*sort(rand(10,1))))
tt =
  10×1 timetable
              Time               Var1  
    ________________________    _______
    14-Jun-2022 09:21:07.985    0.79595
    14-Jun-2022 09:21:08.243    0.23337
    14-Jun-2022 09:21:08.543    0.60084
    14-Jun-2022 09:21:08.585    0.11246
    14-Jun-2022 09:21:08.840    0.51577
    14-Jun-2022 09:21:08.913    0.83784
    14-Jun-2022 09:21:09.180    0.92079
    14-Jun-2022 09:21:09.732    0.49823
    14-Jun-2022 09:21:10.403    0.27761
    14-Jun-2022 09:21:10.574    0.65252
>> tt2 = retime(tt,"secondly","firstvalue")
tt2 =
  4×1 timetable
              Time               Var1  
    ________________________    _______
    14-Jun-2022 09:21:07.000    0.79595
    14-Jun-2022 09:21:08.000    0.23337
    14-Jun-2022 09:21:09.000    0.92079
    14-Jun-2022 09:21:10.000    0.27761