Shifting %tc variables by an hour

[William Blackmon]

Hi everyone,

I'm trying to shift a datetime (format %tc) variable by an hour. Since tc variables are stored in milliseconds from Jan 1 1960, I assumed I needed to simply add the number of milliseconds in an hour to the variable, 60*60*1000.

Starting with some dummy data...

* Example generated by -dataex-. To install: ssc install dataex
clear
input double tcvar
1895225095000
end
format %tc tcvar

Then I'll create a new variable, tcvar_shifted, with 60*60*1000 added to it

gen tcvar_shifted = tcvar + 60*60*1000
format tcvar_shifted %tc
list

My original tcvar was "21jan2020 11:24:55", and my shifted variable is "21jan2020 12:23:57".

So it almost works, but for some reason seems to be adding 58 seconds less than an hour. Any ideas why this might be?

[Nick Cox]

Your new variable needs to be double too.

help datetime

has this advice or warning many, many times, although I guess everyone dealing with dates forgets occasionally. Well, I do, just not in public.

[William Blackmon]

Ahh of course, thank you!