Using datenum for fraction of a second

I am looking for a ways to convert some dates into datenum, given their special format. My dates look as follows:

'2017-02-28 21:36:51'

'2017-02-28 21:36:51.5'

'2017-02-28 21:36:52'

'2017-02-28 21:36:52.5'

'2017-02-28 21:36:53'

'2017-02-28 21:36:53.5'

etc. etc. etc.

In other words, the format of the dates alternates, such that every other entry has an additional 500 milliseconds at the end of it. How can I convert these to datenum simultaneously, given their different formats? (or at least, how can I convert dates with .5 to datenum?). I cannot skip or ignore any of this data.

Thanks

[Walter Roberson]

Would datetime format instead of datenum format be acceptable?

datenum() tends to be more flexible in format conversion but sometimes datetime() is easier.

Answer 1

[Walter Roberson]

dates = {'2017-02-28 21:36:51'
         '2017-02-28 21:36:51.5'
         '2017-02-28 21:36:52'
         '2017-02-28 21:36:52.5'
         '2017-02-28 21:36:53'
         '2017-02-28 21:36:53.5'};

temp = regexprep(dates, ':\d\d$', '$&.0', 'lineanchors');

Now temp is in consistent format

[Bruno Rodriguez]

Thank you, that certainly helps to make them consistent. However, I'm still unsure how to apply datenum to such a format. I seem to be getting two different datenum outputs for the first two cases above, but when I convert the second one back to datestr to double check, it still returns 21:36:51, even though it has a .5

[Walter Roberson]

datestr(datenum(temp), 'YYYY-mm-DD hh:MM:ss.fff')