"Is it possible to get their [variant input and ambiguous formats - sic] datenum correctly in a holistical way?"
"Possible?" Maybe. Not easily, no
The first isn't possible to know if it stands alone whether it is Sept 1 or Jan 9 w/o worrying about century. If there are more values of the same format, one can scan until finds a field that is illegal with one interpretation and then presume the other. That's what the input routines do if not given a format string.
The second, of course, is trivial to convert once given the location of the pieces, but neither datenum nor datetime will handle mixed metaphors well automagically as both try to use the first convertible format they can decipher for the entire input array.
However, if you really can't fix the input format and can stand the overhead, datenum is somewhat more forgiving than datetime and you can try calling each in turn instead of as a group--then either datenum or datetime will try to figure out each on its own since has only the one string at a time. This, of course, will introduce a lot of overhead as the input parsing/detection logic is called every time for a random input format.
>> dstr
dstr =
2×1 cell array
{'9/1/19' }
{'31-Dec-2020'}
>> datenum(dstr)
Error using datenum (line 190)
DATENUM failed.
Caused by:
Error using dtstr2dtvecmx
Failed to convert from text to date number.
>> for i=1:2,datestr(datenum(dstr(i))),end
ans =
'01-Sep-2019'
ans =
'31-Dec-2020'
>>
>> datetime(dstr)
Warning: Successfully converted the text to datetime using the format 'MM/dd/uuuu', but the format is ambiguous and could also be 'dd/MM/uuuu'.
To create datetimes from text with a specific format call:
datetime(textinput,'InputFormat',infmt)
> In guessFormat (line 96)
In datetime (line 632)
ans =
2×1 datetime array
01-Sep-0019
NaT
>>
>> for i=1:2,datetime(dstr(i)),end
Warning: Successfully converted the text to datetime using the format 'MM/dd/uuuu',
but the format is ambiguous and could also be 'dd/MM/uuuu'.
To create datetimes from text with a specific format call:
datetime(textinput,'InputFormat',infmt)
> In guessFormat (line 67)
In datetime (line 632)
ans =
datetime
01-Sep-0019
ans =
datetime
31-Dec-2020
>>
And, of course, the above is only for two specific examples, all kinds of other things could happen even with datenum besides the above for other cases.
I don't know if anybody may have tried to build such a tool on File Exchange or not; would be first place I'd look, but fixing it at the input source would still be my recommendation and first choice by far.
