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

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Ashfaq Ahmed
Ashfaq Ahmed 2022-12-20
编辑： Ashfaq Ahmed 2022-12-20
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!!

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采纳的回答

KSSV
KSSV 2022-12-20
  2 个评论
Ashfaq Ahmed
Ashfaq Ahmed 2022-12-20
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.

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更多回答（1 个）

Steven Lord
Steven Lord 2022-12-20
Ran in:
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
  1 个评论
Ashfaq Ahmed
Ashfaq Ahmed 2022-12-20
编辑：Ashfaq Ahmed 2022-12-20
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!!

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