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st: turning numbers into dates


From   Ekaterina Hertog <ekaterina.hertog@sociology.ox.ac.uk>
To   statalist@hsphsun2.harvard.edu
Subject   st: turning numbers into dates
Date   Sun, 03 May 2009 14:47:31 +0100

Dear all, 
I have got a variable containing the month and year an individual started his or her education. Only Stata thinks the values in this variable are numbers and I want to turn them into dates.
If all the numbers followed the same pattern that will not be a problem.

for example I could do it like this:
tostring edu_start_date_1, gen(stredu1st)
gen edu1st = date(stredu1st, "YM")

My problem is that while most dates in my dataset come in the yyyymm pattern:
e.g.
      +----------+
       | stredu~t |
       |----------|
    1. |        . |
    2. |   197104 |
    3. |   197504 |
    4. |   196504 |
    5. |   196904 |
       |----------|

several contain only yymm
e.g.

       +-----------+
       | edu_st~1  |
       |-----------|
12338. |     8804  |
13265. |     8404  |
13666. |     6304  |
13831. |     8304  |
       +-----------+

So when I run 

gen edu1st = date(stredu1st, "YM")

all the yymm values in stredu1st are turned into missing values in edu1st.

I could of course edit the values containing only yymm into yyyymm pattern  manually, but this feels imprecise and prone to error and I would like to automate the process if at all possible.
Is there a way to make the date command recognise alternating patterns?
I would be very grateful for any advice,
Sincerely yours,
Ekaterina

-- 
Ekaterina Hertog (nee Korobtseva)
Nissan Institute of Japanese Studies
27 Winchester Road, Oxford
OX2 6NA

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