Date formats 'uuuu' vs 'yyyy', 'mm' vs 'MM'

Hello,

Can anyone explain to me when to use "uuuu" for years, upper or lower case for m month?

'dd/mm/yyyy HH:MM'
or
'dd/MM/uuuu HH:mm'
for '14/03/2021 07:30' (14th of March 2021 at 7.30am)

Some functions seem to use one format and others the other one. Every time I try with one, it's the other one.

Is there a certain logic behind this?

[Stephen23]

"Is there a certain logic behind this?"

Yes.

The older functions DATENUM, DATESTR, and DATEVEC all use a very simple TMW-defined format where:

• time components are uppercase,
• date components are lowercase (apart from Q for year quarter).

Then for much newer DATETIME they changed to a different format which:

• also specifies timezones, and other useful date features,
• is consistent with the Unicode Locale Data Markup Language (LDML) international standard (but does not implement all of it).

See: https://unicode.org/reports/tr35/tr35-dates.html#Contents

https://blogs.mathworks.com/loren/2015/02/12/introduction-to-the-new-matlab-data-types-for-dates-and-time/

https://www.mathworks.com/matlabcentral/answers/455275-import-csv-file-using-readtable-gives-wrong-date-time-format#comment_693411

Answer 1

[Adam Danz]

The confusion is warranted and due to inconsistencies in Matlab's date-time formats.

datetime format uses MM/mm for months/minutes but datestr, datenum, and datevec use mm/MM for months/minutes. A recent comment in the forum highlights how difficult it is to detect the error caused by using the wrong case in datetime values.

Learn about uuuu/yyyy in the documentation.

• u, uu, etc are ISO years which are negative for BCE years.
• y, yy, etc are regular years (better term than regular?)

Examples:

datetime('today','format','yyyy-MM-dd G') - years(3000)

ans = datetime
   0980-03-04 BCE

datetime('today','format','uuuu-MM-dd G') - years(3000)

ans = datetime
   -0979-03-04 BCE

[Cris LaPierre]

Moving my answer here since we essentially said the same thing. I avoid using datestr, datenum, and datevec.

I'm not sure I can give an explanation, but it is my experience that it depends on if I'm creating a datetime or a duration, and perhaps if I am setting the input format or the display format.

I have found the tables here helpful for datetimes, and the details provided here helpful for durations.

Generally

• HH = 24 hr format
• hh = 12 hr format
• MM = month
• mm = minute
• uu format will use negative numbers for years before 1 BCE

[John Taylor]

Great explaination! thank you so much