How to convert table variable to datetime and adjust timezone?

Hi there! I have a table that reads a csv file for which column A is "Time" and is in posix-millisec format. I would like to convert the values to dd-mm-yyyy format and then convert values into the time zone which the data were taken. I would like these newly formatted versions of the values to replace the originals in my table. Here is what I have put together so far.

My Table is name "T":

The following line works fine and the resultant dates are at UTC time:

T.Time = datetime(T.Time,'ConvertFrom','epochtime','TicksPerSecond',1e3,'Format','dd-MMM-yyyy HH:mm:ss.SSS')

The following line appears to work, but I am not sure how to check, and I think tells Matlab that the table variable Time is in UTC timezone so that it can be converted with subsequent commands.

T.Time = datetime(T.Time, "TimeZone","UTC")

This is where I get lost: How can I convert all of the values in T.Time to be in 'America/New_York' timezone so that when I plot T.Time vs <Stuff> my time axis reads in New York time?

I tried the following but it throws an error "Error using . To assign to or create a variable in a table, the number of rows must match the height of the table."

T.Time = 'America/New_York'

Thank you!

Answer 1

[Cris LaPierre]

For changing time zones, follow this example: https://www.mathworks.com/help/matlab/matlab_prog/specify-time-zones.html#SpecifyTimeZonesExample-4

I'm assuming the intial conversion to datetime is correct

Time = 1714509608*1e3; % milliseconds since 1/1/1970 0:00:00 UTC
T = table(Time);
T.Time = datetime(T.Time,'ConvertFrom','epochtime','TicksPerSecond',1e3,'Format','dd-MMM-yyyy HH:mm:ss.SSS')

T = table
              Time          
    ________________________

    30-Apr-2024 20:40:08.000

% Assign time zone
T.Time.TimeZone = "UTC"

T = table
              Time          
    ________________________

    30-Apr-2024 20:40:08.000

T.Time.TimeZone

ans = 'UTC'

% Convert to new Time Zone
T.Time.TimeZone = "America/New_York"

T = table
              Time          
    ________________________

    30-Apr-2024 16:40:08.000

T.Time.TimeZone

ans = 'America/New_York'

[Cris LaPierre]

You could simplify a little by specifying the time zone as a name-value pair in datetime

Time = 1714509608*1e3;
T = table(Time);
T.Time = datetime(T.Time,'ConvertFrom','epochtime','TicksPerSecond',1e3,'Format','dd-MMM-yyyy HH:mm:ss.SSS',...
    TimeZone="UTC")

T = table
              Time          
    ________________________

    30-Apr-2024 20:40:08.000

% Check timezone
T.Time.TimeZone

ans = 'UTC'

% Now convert timezone
T.Time.TimeZone = "America/New_York"

T = table
              Time          
    ________________________

    30-Apr-2024 16:40:08.000

% Check timezone
T.Time.TimeZone

ans = 'America/New_York'

[casey]

Awesome thanks @Cris LaPierre!