Convert date to specific format julian date

Need to convert calendar date to Julian date in a specific format (YYDDD). Ex: Day = (2016-05-04,2016-08-24,2016-12-31) J-Day = (16125,16237,16366)

Any help would be appreciated. Thanks.

Answer 1

[Gareth Thomas]

Datetime works nicely. I believe it came out in R2014b.

see the Datetime function

a = datetime('2016-05-04');
a.Format='yyddd'

[Gareth Thomas]

Sorry you also may need to use the command days , that calculates the number of days.

[Charlie Wood]

The result come out as:

a = 16004

Any way to get the actual day in the year number (125)? Thanks.

[Peter Perkins]

If you are looking to get a string, Gareth was on the right track, just off by case:

>> a = datetime('2016-05-04')
a = 
  datetime
   04-May-2016
>> char(a,'yyDDD')
ans =
    '16125'

Of course, the whole point of datetime is to not have to convert between representations all the time, so perhaps

>> a.Format='yyDDD'
a = 
   16125

would serve as well. If you want a number, then your accepted answer is the way to go.

[Charlie Wood]

Peter/Gareth, this is perfect. Switching the ddd to DDD was the fix needed in the a.Format.

>> a = datetime('2016-05-04');
>> a.Format='yyDDD'
a = 
   16125

This works for any year as well which is great. This will be new accepted answer vice the numerical version I put up.

Thanks a gain for the help!

Answer 2

[Steven Lord]

Create a datetime array from the char vectors containing the yyyy-MM-dd form of the dates. Use the juliandate function to compute the Julian date from the datetime array.

[Charlie Wood]

 d = '2016-12-31';
 dt = datetime(d) 
dt = 31-Dec-2016
 j = juliandate(dt) 
j = 2.4578e+06

How do I get j into the yyddd format (to read 16366)?

Thanks.

Answer 3

[Michael C.]

My understanding was that Julian usually referred to the number of days since Jan 1 4713 BC, but judging by your example, you are using March 11th, 1972.

Either way, you can get number of days by doing a subtraction on two "datenum"s

datenum([2016 08 24 0 0 0]) - datenum([1972 3 11 0 0 0])

which gives the 16237. Passing in a string for the date will also work.

[Charlie Wood]

This worked pretty effectively. Unfortunately if I have a date from 2015 or 2014 (which I do), it doesn't work as well. I guess I can put an if statement in there to switch the second datenum to the right value. Thanks so much Michael.

Answer 4

[Charlie Wood]

Here's what I got combining some answers:

d = '2016-05-04';
dt = datime(d);
jday = (year(dt)-2000)*1000 + day(dt,'dayofyear')

The answer comes out with 16125. It's not pretty and not useful for dates before the year 2010 (maybe with some minor formatting it would be ok for 2000-2009). It does however work for my 2014-2016 dates so far.

Thanks to everyone for the help and input!!!

Answer 5

[Ankit Kanthe]

Here's what I got combining some answers:

d = '2016-05-04'; dt = datime(d); jday = (year(dt)-2000)*1000 + day(dt,'dayofyear') The answer comes out with 16125. It's not pretty and not useful for dates before the year 2010 (maybe with some minor formatting it would be ok for 2000-2009). It does however work for my 2014-2016 dates so far.