Date Arithmetic

[Yao Zhao]

If you need to add (or subtract) a period measured in days to a date, it is straightforward to do so. Just remember to format all new date variables as dates with %td:

gen a = td(19oct2005) - 28
format %td a

My question is that, in all cases, I don't need a variable. I only need to know the outcome. Even if I generate a new variable, it's useless for me and I will drop it. Thus, I am thinking that just generate a scalar. But then I realize that format %td a will not work for a scalar.

[Rich Goldstein]

you say you "only need to know the outcome" - in that case, -display- will do it for you;

di td(19oct2005) - 28

if you want it in a local; just do:

local junk= td(19oct2005) - 28

just replace "junk" with whatever you want to call the local; you can check the result via:

mac li _junk

[Nick Cox]

As a small variant on @Rich Goldstein's answer I find mdy() convenient too.

[Yao Zhao]

I need to do this code:

keep if (date<td(19oct2005)) & (date>=td(21sep2005))

But I need to show how to get 21sep2005. So I did:

generate a = td(19oct2005) - 28
format %td a
drop a

[Nick Cox]

So, did you want

keep if inrange(date, mdy(10, 18, 2005) - 27, mdy(10, 18, 2005)

or

keep if inrange(mdy(10, 18, 2005) - date, 0, 27)