Inconsistency when assigning to the 'Month' property of a datetime array in a timetable

I imported a timetable from an excel file and had to adjust some parts of the datetime array afterwards, since the original excel file had no information on the day, month, or year of the time column.

Since that info was missing from the input file, Matlab auto-filled the date so that I get a time column with entries like "1899-12-31 10:15:10". This matches the datetime format I set up in the import options - "yyyy-MM-dd HH:mm:ss".

Since I wanted to adjust the date to "2024-02-15", I used dot notation first for the year:

Table.TimeColumn.Year = 2024

This gave me the expected result of "2024-12-31 10:15:10". Where it gets weird is trying to change the month to February; if I enter something like this:

Table.TimeColumn.Month = 2

The days of the datetime values get changed to "2" instead, and the month is set to March, like this: "2024-03-02 10:15:10".

What's even stranger is that assigning the month value to "1" or "3" does not replicate this behavior. Using those values changes the month as expected.

But when assigning the datetime's month to "2", I can only change the month to my desired value if I make another dot notation assignment for it after the first one, or assign it after adjusting the day value, such that this

Table.TimeColumn.Year = 2024

Table.TimeColumn.Month = 2

Table.TimeColumn.Day = 15

puts out "2024-03-15", while this

Table.TimeColumn.Year = 2024

Table.TimeColumn.Day = 15

Table.TimeColumn.Month = 2

puts out "2024-02-15" in my timetable column.

Is this possibly a bug, or am I not understanding the format correctly?

Answer 1

[Steven Lord]

From the old rhyme, "Save February at twenty-eight, // But leap year, coming once in four, // February then has one day more."

What is February 31st? It's a non-standard date.

dt = datetime(2024, 2, 31)

dt = datetime
   02-Mar-2024

It ought to be February 29th plus two calendar days, right? Since 29 + 2 = 31.

dt = datetime(2024, 2, 29) + caldays(2)

dt = datetime
   02-Mar-2024

You'd run into this same scenario with changing the month of a datetime from a 31-day month to a 30-day month. For example, March has 31 days while April has 30 but not 31.

dt1 = datetime(2024, 3, 31)

dt1 = datetime
   31-Mar-2024

dt2 = datetime(2024, 4, 30)

dt2 = datetime
   30-Apr-2024

If I change dt1's Month to be April, it becomes May 1st aka "April 31st".

dt1.Month = 4

dt1 = datetime
   01-May-2024

dt3 = datetime(2024, 4, 31)

dt3 = datetime
   01-May-2024