Convert timestamps in CSV file to seconds using readtable and table2timetable

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YH 2018-3-11

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评论： YH 2018-3-13

采纳的回答： Jeremy Hughes

acc_20180310_161817_114.csv

Hello,

I found several solutions for converting timestamps to seconds (by eliminating year, month, day...), but none of them worked. How can I use readtable() and table2timetable() for converting the timestamps in my CSV file to seconds? Attached you can find the CSV file. My goal is to plot gX, gY, gZ in terms of time. What is the most efficient way of applying that?

Thanks

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dpb 2018-3-11

编辑：dpb 2018-3-11

First you need to create the input file with sufficient precision to differentiate between samples (or eliminate the repeated timestamps in some fashion).

After you do that, I suspect you'll have better luck using the timeseries object than the datetime or timetable to use linear time instead of calendar time for plotting as the duration time object is hamstrung for less than seconds intervals it appears.

Or, just revert to the old datenum and treat the absicssa as purely numeric and fixup the axes using the datetimeruler manually.

YH 2018-3-11

thanks for the reply. Which function should I use to read the CSV file and import the TimeStamps data to timeseries? Can you give example for using timeseries as required?

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采纳的回答

Jeremy Hughes 2018-3-11

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This will work as long as the times are on the same day (as in the file).

T = readtable(file,'Format','%{dd-MMM-uuuu HH:mm:ss.SS}D%f%f%f')
times = timeofday(T.TimeStamp);
times.Format = 'hh:mm:ss.SSS';
TT = table2timetable(T(:,2:end),'RowTimes',times)

you can also subtract datetimes, which would make them elapsed times since start. Not sure what you're looking for.

times = T.TimeStamp - T.TimeStamp(1)

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dpb 2018-3-12

编辑：dpb 2018-3-13

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OK, Eric, I stand corrected; it was the fignewton of appearance between the default duration format plus YH's insufficient precision in his input data that combined to make me draw the wrong conclusion on what had gone wrong.

Seeing

    >> t(1:10,:)
  ans = 
      TimeStamp       gX           gY          gZ   
      _________    _________    ________    ________
      18:17.3      -0.076035    -0.71863    -0.61618
      18:17.3      -0.082672    -0.74306     -0.6469
      18:17.3       -0.03009    -0.76733    -0.79691
      18:17.3       0.020218    -0.81285    -0.86838
      18:17.3       0.049622    -0.85599    -0.90698
      18:17.3       0.058319    -0.91023    -0.89687
      18:17.3       0.071381    -0.93538    -0.84306
      18:17.4       0.088852    -0.94637     -0.7709
      18:17.4        0.13455    -0.92213    -0.71928
      18:17.4        0.21944    -0.86867    -0.67058
  >> dt=diff(t.TimeStamp);
  >> [min(dt) max(dt)]
  ans = 
    1×2 duration array
     00:00:00   00:00:00
  >>

I fell into the trap that by using max the underlying data would have been revealed; while there is some convenience in being able to set the format there's some idiosyncracies that come along with it, one being the above that small but non-zero values don't show. (That's also true w/ default double format but that's where the min/max "trick" generally reveals the truth whereas needs must remember that doesn't carry over with time formats.)

I also don't like the limited choice of output formats for a duration; it wouldn't accept just 'ss.SSS', for example, if one did want to see it in cumulative seconds as YH asked for in original ?.

Thanks for the follow-up...

dpb 2018-3-13

Depending upon what you're trying to do with the data you might also be able to interpolate the time vector to backfill the missing times accurately enough...

YH 2018-3-13

Yep, it might help too

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