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matlabtimemilliseconds

Matlab: Convert file date with milliseconds into Matlab time format

I have some text files with dates of the form

2015-09-08 14:38:03

2015-09-08 14:38:03.1

2015-09-08 14:38:03.2

that I want to convert into Matlab date/time format. As you can see, the text strings have a different time format regarding the milliseconds. In the first case, no milliseconds are given; in the seconds case, milliseconds are given with one digit only. This gives a sampling rate of 20Hz for measuring data.

So far, only

x = datenum(file.dateColumn, 'yyyy-mm-dd HH:MM:SS');

is working, but of course misses the milliseconds. A conversion like

x = datenum(file.dateColumn, 'yyyy-mm-dd HH:MM:SS.FFF');

does not work as the milliseconds are either zero (full seconds) or have one digit after the '.' delimiter. A workaround like

x = datestr(file.dateColumn, 'yyyy-mm-dd HH:MM:SS.FFF');

x = datenum(file.dateColumn, 'yyyy-mm-dd HH:MM:SS.FFF');

i.e. converting the text string into a Matlab string (and giving it additional FFF/FF digits) and then converting that one into a date/time number works - but this is such time-cosuming that I cannot use it for my data. I have millions of time rows in different files.

Do you have any ideas?

Greetings, Arne

Solution

  • Thanks to Nick I found a way to solve it:

    dataVelPres = readtable(fileName, ...
    'ReadVariableNames', false, ...
    'HeaderLines', 4 );

dataVelPres.Properties.VariableNames = {'date' 'velU' 'velV' 'velW' 'pres'};

dateMill = datetime(dataVelPres.date, 'inputformat', 'yyyy-MM-dd HH:mm:ss.S');
dateFull = datetime(dataVelPres.date, 'inputformat', 'yyyy-MM-dd HH:mm:ss');

dateNaT = isnat(dateMill);
dateMill(dateNaT) = dateFull(dateNaT);
dataVelPres.dateTime = dateMill;
dataVelPres.date = datenum(dataVelPres.dateTime); % Convert to number format if needed

    This works with two tables - one for millisec. and one without - and puts both together, as both give NaT entries in case the inputformat does not match.

    Is there a more elegant way?