Convert day of year to Date?

I want help converting 1 to 1st Jan; 365 to 31st Dec and so on. Basically I want to convert day number of a year into the actual date it corresponds to. Any help will be greatly appreciated. I have done the inverse using the following code

d = datetime('20-Mar-2018')
Dn = day(d,'dayofyear')

Answer 1

[Pratyush Das]

I finally found the answer I was looking for.

N=10; %you can input any other number,The day in question is the 'N'th day of the year
Dt=datetime('1-Jan-2018')+N-1 % This code will give the date of the 'N'th day.

Answer 2

[Steven Lord]

You want to convert the day number to the date in the current year?

% Get today and the start of the current year
d = datetime('today');
s = dateshift(d, 'start', 'year');

% One approach is to add 77-1 to s (1 January, day 1) to get to day 77
day77a = s + 77 - 1
check_a = day(day77a, 'dayofyear')

% Another approach, shift s to the start of day 77-1 after s
day77b = dateshift(s, 'start', 'day', 77-1)
check_b = day(day77b, 'dayofyear')

% A third approach, create "January 77th" of the current year
day77c = datetime(year(d), 1, 77)
check_c = day(day77c, 'dayofyear')

Answer 3

[Pratyush Das]

I finally found the answer I was looking for. Suppose the Day in question is the 'N'th day of the year. Then the following code will give the exact date corresponding to that day.

Dt=datetime('1-Jan-2018')+N-1

[Peter Perkins]

Sort of. If you are working with timezones, best to use

Dt = datetime(year,1,0) + caldays(N)

to account for the fact that twice a year, the day is not 24 hours. But if you already know the year, why not just

dt = datetime(year,1,N)

[Sreeraj T]

@Peter Perkins, this is nice suggestion. I have a question in this regard: in my data I know that year is 2019, which implies that 307 corresponds to 03-Nov-2019.

I also do have another number ' 307.234426997'. How can I convert extract time from it?

Thanks in advance.

[jeremy]

307.234426997 = the 307th day and .234426997 of that day. To convert the decimal to a time multiply

24 * .234426997 = 5.626247928 which means 5 am and change.

60 * .626247928 = 37.57487568 which means 37 mins and change.

60 * .57487568 = 34.4925408

So the full timestamp would be '2019-11-03 05:37:34.493'

[Steven Lord]

You could split the function into the integer part 307 and the fractional part 0.234426997 using floor and subtraction.

x = 307.234426997

x = 307.2344

numFullDays = floor(x)

numFullDays = 307

numPartialDays = x - numFullDays

numPartialDays = 0.2344

dt2 = datetime(2019, 1, numFullDays) + days(numPartialDays)

dt2 = datetime
   03-Nov-2019 05:37:34

dt2.Format = dt2.Format + ".SSSSSS"

dt2 = datetime
   03-Nov-2019 05:37:34.492540

[Sreeraj T]

@jeremy @Steven Lord Thanks