extracting year from an elapsed and formatted date

[Camila Plaza]

Dear all,

I am having an issue extracting the year from my date variable.

My date variable is already elapsed and formatted in a way that I can read the year followed by the month. Eg: 2013m1, 2013m2, ..... , 2015m12 - this variable is called modate

Now I need a variable that shows me only the year. I tried generating a variable year=modate and then formatting it so that it only displays the year;


gen year=modate
format year %ty

but then I get strange results such as 1961 or numbers like 636.

Can someone help me out?

Thanks!!
Cami

[Daniel Bela]

Hi Camila,

please have a look at the FAQ (also linked from the top of each page) to learn how to post questions in a way so that we can answer them quickly. This involves using code delimiters, and sharing example data using -dataex-.

If you don't, our answers are mainly guesswork. It is these kinds of questions that don't get answers quickly, because most experienced users here don't like guesswork.

Thus said, here's my guesswork on your topic: From what you write, I assume you have a Stata Internal Format (SIF) date variable, correctly formatted:

* make up example data
clear
set obs 36
generate modate=_n+635
format modate %tm
list

Note that Stata internally stores a monthly date as "months counted from January, 1960". This means that January, 2013 equals month number 636. See -help datetime- for background information on this; it is a good idea to read through it in order to understand the concept.

Converting this month count to a year number is, mathematically, nothing more than dividing it by 12 and adding 1960 to the result:

* manually converted
generate manual_year=((modate / 12) + 1960)

However, to perform these kinds of conversion tasks, Stata has a few more elaborate functions for it; see -help datetime, marker(s6)-. They can, for instance, account for leap seconds, which a manual function cannot (this is not required in your example, but it may be with other conversion tasks). So, the Stata way to do your conversion would be:

* Stata-ish converted
generate year=yofd(dofm(modate))

Kind regards
Bela