Can I get a datetime output in a different Time Zone from the input Time Zone in one function call?

d = datetime('2016-Jan-20 12:00:00','TimeZone','UTC')

and then

d.TimeZone = 'America/New_York'

gets me the transformed time from the input... is there any way to get this answer in the original function call, without haveing the 2nd command? I know there is a Format option, but I cannot see how one can add a TimeZone in that. transform the input TimeZone.

Answer 1

[Walter Roberson]

d = subsasgn(datetime('2016-Jan-20 12:00:00','TimeZone','UTC'), struct('type', '.', 'subs', {'TimeZone'}), 'America/New_York');

You might want to create a help function for that, like

sset = @(var, sub, val) subsassgn(var, struct('type', '.', 'subs', {sub}), val);

and then

sset(datetime('2016-Jan-20 12:00:00','TimeZone','UTC'), 'TimeZone', 'America/New_York')

or

datetimeNY = @(date) subsasgn( datetime(date, 'TimeZone', 'UTC'), struct('type', '.', 'subs', {'TimeZone'}), 'America/New_York');

which you could then use as

d = datetimeNY('2016-Jan-20 12:00:00');

[Jeff Waldron]

Walter,

Thank you... that's great... I have seen subsasgn in a couple other answers on other topics, but I've never used it, and thus always forget about it's capabilitities... Appreciate the direction.

Answer 2

[Peter Perkins]

I think this also does what you want:

>> d = datetime('2016-Jan-20 12:00:00 UTC','InputFormat','yyyy-MMM-dd HH:mm:ss z','TimeZone','America/New_York')
d = 
  datetime
   20-Jan-2016 07:00:00

but it requires that 'UTC' be appended to each timestamp. So choose your poison: is calling subsasgn directly better or worse? The only reason I can think to need one line is that you're writing an anonymous function.

[Walter Roberson]

subsasgn is admittedly ugly!

Answer 3

[Maitreyee Mordekar]

Hi Jeff,

The following command will help you set the desired functionality-

d = datetime('2016-Jan-20 12:00:00','TimeZone','America/New_York');

The following link is the reference documentation for 'datatime' function-

https://in.mathworks.com/help/matlab/ref/datetime.html

[Walter Roberson]

That does not quite do what Jeff needs. Jeff needs to create a time in UTC and then shift it to New York timezone. The time that would be created by the command you show would differ by 5 hours from the time created by the commands that Jeff shows.

[Peter Perkins]

Just to expand a bit on this:

If you assign the TimeZone property of an unzoned datetime, the result will "look" the same, in other words, it becomes the same clockface time in a specific time zone.

On the other hand, if you assign the TimeZone property of a datetime that's already in a specific time zone, the instant in time remains the same, but it "looks" different because of the different time zone offsets. So what Walter is saying is that creating a datetime at 12pm in UTC, and then setting its TimeZone property to America/New_York results in 7am, New York time. Same instant, different timestamp.