How to convert datetime to day of the year when there are more than one year?

Hi!

If I have an array of datetime like this -

'2003-10-14'
'2003-11-07'
'2003-11-15'
'2003-11-23'
'2004-01-10'
'2004-04-07'
'2004-10-08'
'2005-01-04'
'2005-01-20'
'2005-05-28'
'2005-06-05'
'2005-09-17'
'2005-11-20'
'2006-02-08'
'2006-02-16'
'2006-02-24'
'2006-03-04'
'2006-03-12'

How can I convert this datetime array as the day of the year? My day of the year should start from 2003-01-01 (= day 01). Once I reach 2004-01-01, it should be day 366. For the 2005-01-01, it should be day 731 and so on. Can any one kindly tell me how can I convert the whole array into a day of the year array?

Any feedback from you will be highly appreciated!!

Answer 1

[KSSV]

Read it here: https://in.mathworks.com/help/matlab/ref/datetime.day.html

[Les Beckham]

You might want to also read about the caldays function: https://www.mathworks.com/help/matlab/ref/calendarduration.caldays.html

[Ashfaq Ahmed]

Hi! Thank you for the link. But the problem is, when my date is 2003-01-10 and 2004-01-10 the conversion shows it's the 10th day of the year (which is correct for individual year). But for my calculation, I need it to be 10 and 375.

Answer 2

[Steven Lord]

Let's look at your sample data.

data = {'2003-10-14'
'2003-11-07'
'2003-11-15'
'2003-11-23'
'2004-01-10'
'2004-04-07'
'2004-10-08'
'2005-01-04'
'2005-01-20'
'2005-05-28'
'2005-06-05'
'2005-09-17'
'2005-11-20'
'2006-02-08'
'2006-02-16'
'2006-02-24'
'2006-03-04'
'2006-03-12'};
dt = datetime(data);

What's the first date in your data array? I'm not going to assume it's the first element of data.

firstdate = min(dt)

firstdate = datetime
   14-Oct-2003

What's the start of that first date's year?

firstOfYear = dateshift(firstdate, 'start', 'year')

firstOfYear = datetime
   01-Jan-2003

How many calendar days have elapsed between the 1st of January of that earliest year and each element of your data?

elapsedTime = between(firstOfYear, dt, 'Days')

elapsedTime = 18×1 calendarDuration array
    286d
    310d
    318d
    326d
    374d
    462d
    646d
    734d
    750d
    878d
    886d
    990d
   1054d
   1134d
   1142d
   1150d
   1158d
   1166d

Let's convert that into double. Note I need to add 1 because elapsedTime is the time between January 1st and your data but you want the number of those dates. There's 0 days between January 1st and January 1st but January 1st is day 1 of the year.

d = caldays(elapsedTime)+1

d = 18×1

287 311 319 327 375 463 647 735 751 879

[Ashfaq Ahmed]

Excellent!! I was manually adding 365 days once I have a new year and my code looked that big -

DOY2 = day(dt,'dayofyear');
DOY2(19:48)   = 365*1+DOY2(19:48);
DOY2(49:85)   = 365*2+DOY2(49:85);
DOY2(86:117)  = 365*3+DOY2(86:117);
DOY2(118:150) = 365*4+DOY2(118:150);
DOY2(151:183) = 365*5+DOY2(151:183);
DOY2(184:217) = 365*6+DOY2(184:217);
DOY2(218:249) = 365*7+DOY2(218:249);
DOY2(250:279) = 365*8+DOY2(250:279);
DOY2(280:293) = 365*9+DOY2(280:293);
DOY2(294:328) = 365*10+DOY2(294:328);
DOY2(329:366) = 365*11+DOY2(329:366);
DOY2(367:401) = 365*12+DOY2(367:401);
DOY2(402:436) = 365*13+DOY2(402:436);
DOY2(437:470) = 365*14+DOY2(437:470);
DOY2(471:501) = 365*15+DOY2(471:501);
DOY2(502:540) = 365*16+DOY2(502:540);
DOY2(541:574) = 365*17+DOY2(541:574);
DOY2(575:610) = 365*18+DOY2(575:610);

You just made the whole calculation so easy and smart. Great thinking process!!