Why aren't my locale times converted to UTC time?

Hello all,

I would like to convert some dates that are taken with the Amsterdam TimeZone into UTC TimeZone, reading Matlab doc I should use datetime combined wit the the TimeZone option. I have done so, but my time once converted keeps staying in the Amsterdam local time, I know that it should be two hours less in UTC.

Here below the proccess I use, myDatesLocal are Amsterdam timezone based, so array b should stay the same as it does, however, array a should change to two ours earlier. I would expect somehting like 12-Apr-2018 12:51:36 for the first date.

K>> myDatesLocal = myDates(1:3)

myDatesLocal =

    3×1 cell array

      '12/04/18 14:51:36'
      '12/04/18 14:52:36'
      '12/04/18 14:53:36'

K>> b =datetime(myDatesLocal,'InputFormat','dd/MM/yy HH:mm:ss','TimeZone','Europe/Amsterdam')

b = 

    3×1 datetime array

     12-Apr-2018 14:51:36
     12-Apr-2018 14:52:36
     12-Apr-2018 14:53:36

K>> a =datetime(myDatesLocal,'InputFormat','dd/MM/yy HH:mm:ss','TimeZone','UTC')

a = 

    3×1 datetime array

     12-Apr-2018 14:51:36
     12-Apr-2018 14:52:36
     12-Apr-2018 14:53:36

What am I doing wrong?

Thanks in advance!

Answer 1

[Guillaume]

No, when you create your a, you're simply telling matlab that the 14:51 is measured in the UTC timezone. At no point do you tell matlab that it is measured in Amsterdam timezone but to be displayed in UTC.

The correct way to do what you want is to create your datetime in the Amsterdam timezone, then tell matlab to change the timezone to UTC:

>> myDatesLocal = {'12/04/18 14:51:36'
                   '12/04/18 14:52:36'
                   '12/04/18 14:53:36'};
>> b = datetime(myDatesLocal,'InputFormat','dd/MM/yy HH:mm:ss','TimeZone','Europe/Amsterdam')
b = 
  3×1 datetime array
   12-Apr-2018 14:51:36
   12-Apr-2018 14:52:36
   12-Apr-2018 14:53:36

>> b.TimeZone = 'UTC'
b = 
  3×1 datetime array
   12-Apr-2018 12:51:36
   12-Apr-2018 12:52:36
   12-Apr-2018 12:53:36

[Javier]

Thanks Guillaume, it works perfectly now!

[Peter Perkins]

To explain what's was going on:

Calling the datetime constructor on a datetime and specifying TimeZone more or less says, "make me a new datetime array that looks like this old one, but has this new time zone." Setting the Format property says, "shift this array's times to be in this new time zone."

An additional thing you might do is add a TZ specifier to the format so there's no question, perhaps 'dd/MM/yy HH:mm:ss z'.

[Javier]

Thanks Peter, could you explain a bit more what time zone I should specify in with the z option?

[Peter Perkins]

I don't understand the question. 'z' is something you would add to the display format of a datetime to show the (offset of) the time zone your array is set to. doc datetime.Format.