Convert from Coordinated UTC to datetime?

I have a list of times formatted in coordinated UTC time. For example, the first data entry point I have is

1.511092230713565e+05

where the first six digits are the year, month and day (so 11/09/2015) and the rest of the digits are the fraction of the day. How do I extract the the first six digits and then convert the rest of the digits so I can convert the time to a datenum array?

Answer 1

[Dave B]

You can do this easily with datetime:

x=1.511092230713565e+05;

% The date part is the part before the decimal, so use floor
d = datetime(string(floor(x)),'InputFormat','yyMMdd') 

d = datetime
   09-Nov-2015

% The time part is fractions of a day, remove the date part and call days
% to get a duration
t = days(x-floor(x))

t = duration
   0.22307 days

% The result is the date part (which will be midnight) plus the fraction of
% a day
dt = d+t 

dt = datetime
   09-Nov-2015 05:21:13

% If you really must use datenum (though this is not recommended, datetime is so much better!)
datenum(dt)

ans = 7.3628e+05

Answer 2

[Star Strider]

A different approach —

format long g
nr = 1.511092230713565e+05;
dt = datetime(num2str(fix(nr)),'InputFormat','yyMMdd') + timeofday(datetime(datevec(rem(nr,1))))

dt = datetime
   09-Nov-2015 05:21:13

dn = datenum(dt)

dn = 
          736277.223071357

Also, Specify Time Zones might be of interest.

.

[Dave B]

I like the rem(nr,1) better than my x-floor(x), and I think fix is technically the accurate choice if there might be some BC dates?

Less sure about timeofday(datetime(datevec())) vs. days()