# how to read day of the year as datetime ?

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pruth on 25 Jul 2020
Answered: Star Strider on 25 Jul 2020
I have vector of dates, it looks like this
2019001
2019002
.
.
.
2019364
2019365
2019 is year and next number is day of the year.
anybody tell me how to use datenum or datetime here !
I have around 3 years of dara.

per isakson on 25 Jul 2020
Edited: per isakson on 25 Jul 2020
>> chr = sprintf( '%d', 2019364 );
>> sdn = datenum(str2double(chr(1:4)),1,0)+str2double(chr(5:end));
>> datetime( sdn, 'ConvertFrom', 'datenum' )
ans =
datetime
30-Dec-2019 00:00:00
>>
%%
d = [ 2019001; 2019002; 2019364; 2019365 ];
%%
chr = num2str( d );
chr = strjust( chr, 'left' );
sdn = datenum( str2num(chr(:,1:4)), 1, 0 ) + str2num(chr(:,5:end));
dt = datetime( sdn, 'ConvertFrom', 'datenum' )
Outputs
dt =
4×1 datetime array
01-Jan-2019 00:00:00
02-Jan-2019 00:00:00
30-Dec-2019 00:00:00
31-Dec-2019 00:00:00

madhan ravi on 25 Jul 2020
v = regexprep(""+vector,'(\d{4})(\d+)','00/\$2/\$1');
Wanted = datetime(datestr(v))
##### 2 CommentsShowHide 1 older comment
madhan ravi on 25 Jul 2020
For older versions:
v = regexprep(sprintfc('%d',vector),'(\d{4})(\d+)','00/\$2/\$1'); % sprintfc() undocumented
Wanted = datetime(datestr(v))
Days_in_a_year = str2double(regexprep(v, '(\d+)/(\d+)/(\d+)', '\$2'));

Star Strider on 25 Jul 2020
Another approach:
ydv = [2019001
2019002
2019364
2019365]; % ‘YearDay’ Vector
Years_Days = datetime(num2str(fix(ydv/1000)), 'InputFormat','yyyy') + caldays(rem(ydv,1000)-1)
producing:
Years_Days =
4×1 datetime array
01-Jan-2019
02-Jan-2019
30-Dec-2019
31-Dec-2019
Use the 'Format' name-value pair to get the desired output format. The easiest way to do that (for one example) is simply:
Years_Days.Format = 'yyyy-MM-dd';
to get:
Years_Days =
4×1 datetime array
2019-01-01
2019-01-02
2019-12-30
2019-12-31
.