duration between 2 dates

[jeff jennings]

I cannot get duration (in days) to work between two dates Date1 and Date 2.

list Date1: 23mar2021 04:00:00

I changed the format of date1 and dat2 from %tc to %td.
then gen vent_days = date2 - date1


i get vent_days: 2.21e+07
Date2: 1.91e+12
Date1: 1.91e+12


Now sure how I am getting numbers so high they are exponential? The number of days between these dates should be between 1 and 30-ish.

As an update: I realize this is because there are times. So if I have a variable that includes the times not just the date, how do I use state to computer duration?

[Nick Cox]

Do not change the display format thinking that this converts from one date-time type to another. That does not work. See https://journals.sagepub.com/doi/pdf...867X1201200415

There are 24 x 60 x 60000 ms in 1 day, so that should be the difference in ms between just now and 1 day earlier. I use display on sandbox examples.

di 24 * 60 * 60000
86400000

. di clock("1 Nov 2021 18:26:00", "DMY hms") - clock("31 Oct 2021 18:26:00", "DMY hms")
86400000

.. di (clock("1 Nov 2021 18:26:00", "DMY hms") - clock("31 Oct 2021 18:26:00", "DMY hms")) / 864e5
1

In your case, I think it boils down to

gen wanted = (date2 - date1) / 864e5

People seem to hope that they can use date-times without reading the documentation (much), but in practice you need to read as much of

help datetime

as solves your problem.

[jeff jennings]

Do not change the display format thinking that this converts from one date-time type to another. That does not work. See https://journals.sagepub.com/doi/pdf...867X1201200415



In your case, I think it boils down to

gen wanted = (date2 - date1) / 864e5

as solves your problem.

That worked. I hope when future people google "stata date duration between dates" your answer pops up. Every time I googled this, I would get confused but I have a weakness for dates - even when I code in PHP dates are my weak spot!.

[Nick Cox]

To quote myself on a paper that should appear in Stata Journal 22(1) 2022

Dates are complicated.The entire rigmarole of dates (to say
nothing of times too...) is a complicated mess. From
your early education onwards, you have been exposed repeatedly to the
rules you usually need to know, but handling dates in software like
Stata poses a new set of challenges. Some software handles dates through
one or more distinct data or variable types. Stata's decision that dates
and times are just integers simplifies much, but still implies details
about formats and functions that may need mastering. help datetime
remains the best place to start.