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st: dates in stata


From   lschoele@rumms.uni-mannheim.de
To   statalist@hsphsun2.harvard.edu
Subject   st: dates in stata
Date   Wed, 01 Apr 2009 00:59:48 +0200

Hi Statalist,

I added an exchange between Paul and me.
I am using version 9.1
I tried all your suggestions, but nothing worked...
Maybe someone eöse can help me?

Zitat von "E. Paul Wileyto" <epwileyto@verizon.net>:
May I ask what version of Stata you are using?  My version is 10.  This
date conversion goes back to previous versions, but I cannot swear
about 7 or 8, and I cannot swear that older versions will take dates
written like that, with the spaces, and the whole month written out.

I'm going to suggest something off the wall, but can you try...

gen dateval=date( event_date, "D M Y")

with spaces in the DMY?

Also try

gen dateval=date( event_date, "DM20Y")

gen dateval=date( event_date, "D M 20Y")

Just a hunch.

P

lschoele@rumms.uni-mannheim.de wrote:

Hi Paul,
this is what I got. So I guess it is a string???

. des event_date

             storage  display     value
variable name   type   format      label      variable label
-------------------------------------------------------------------------------
event_date      str17   %17s




Zitat von "E. Paul Wileyto" <epwileyto@verizon.net>:
Dots are missing values.  Everyone has been assuming you have dates in
strings.  Could you check this. Type -des event_date

Then look at the format returned.  If it is a string, is will give you
something like %20s.    If it doesn't have that "s" in the format, it
is not a string, and I'll be scratching my head.

P
lschoele@rumms.uni-mannheim.de wrote:

Hi Paul,

thank you very much for your answer. I tried to follow your suggestions.
I don't know what I did wrong, but I just got some dots (see below).
Can you tell me what I am doing wrong?

Best Regards Lisa


. gen dateval=date( event_date, "DMY")
(84 missing values generated)

. list

   +----------------------------------------------+
   |     company_id          event_date   dateval |
   |----------------------------------------------|
1. |       Nintendo         09 May 2006         . |
2. |           Palm         18 May 2005         . |
3. |          Apple     23 October 2001         . |
4. |          Apple   07 September 2005         . |
5. |          Apple     11 January 2005         . |
   |----------------------------------------------|
6. |          Apple     06 January 2004         . |
7. |          Apple   05 September 2007         . |
8. |          Apple     09 January 2007         . |
9. |          Apple      07 August 2007         . |
10. |          Apple         01 May 2001         . |
   |----------------------------------------------|
11. |          Apple     15 January 2008         . |
12. |          Apple     14 October 2008         . |
13. |             LG    11 December 2006         . |
14. |             LG    11 February 2008         . |
15. |        Pioneer     07 January 2008         . |
   |----------------------------------------------|
Zitat von "E. Paul Wileyto" <epw@mail.med.upenn.edu>:
Your date is entered as a string, not a real date format.  Real dates
are integer values, representing (currently) the number of days elapsed
since January 1st 1960.
Try this:

. edit
(1 var, 13 obs pasted into editor)

. list

  +------------------+
  |             var1 |
  |------------------|
1. |    01 April 2005 |
2. |    01 April 2008 |
3. |   01 August 2000 |
4. |   01 August 2001 |
5. |   01 August 2002 |
  |------------------|
6. |   01 August 2003 |
7. |   01 August 2005 |
8. |   01 August 2006 |
9. |   01 August 2007 |
10. |   01 August 2008 |
  |------------------|
11. | 01 December 2000 |
12. | 01 December 2003 |
13. | 01 December 2004 |
  +------------------+

. gen dateval=date( var1, "DMY")

. list

  +----------------------------+
  |             var1   dateval |
  |----------------------------|
1. |    01 April 2005     16527 |
2. |    01 April 2008     17623 |
3. |   01 August 2000     14823 |
4. |   01 August 2001     15188 |
5. |   01 August 2002     15553 |
  |----------------------------|
6. |   01 August 2003     15918 |
7. |   01 August 2005     16649 |
8. |   01 August 2006     17014 |
9. |   01 August 2007     17379 |
10. |   01 August 2008     17745 |
  |----------------------------|
11. | 01 December 2000     14945 |
12. | 01 December 2003     16040 |
13. | 01 December 2004     16406 |
  +----------------------------+

. format  dateval %d

. list

  +------------------------------+
  |             var1     dateval |
  |------------------------------|
1. |    01 April 2005   01apr2005 |
2. |    01 April 2008   01apr2008 |
3. |   01 August 2000   01aug2000 |
4. |   01 August 2001   01aug2001 |
5. |   01 August 2002   01aug2002 |
  |------------------------------|
6. |   01 August 2003   01aug2003 |
7. |   01 August 2005   01aug2005 |
8. |   01 August 2006   01aug2006 |
9. |   01 August 2007   01aug2007 |
10. |   01 August 2008   01aug2008 |
  |------------------------------|
11. | 01 December 2000   01dec2000 |
12. | 01 December 2003   01dec2003 |
13. | 01 December 2004   01dec2004 |
  +------------------------------+

. sort dateval

. list

  +------------------------------+
  |             var1     dateval |
  |------------------------------|
1. |   01 August 2000   01aug2000 |
2. | 01 December 2000   01dec2000 |
3. |   01 August 2001   01aug2001 |
4. |   01 August 2002   01aug2002 |
5. |   01 August 2003   01aug2003 |
  |------------------------------|
6. | 01 December 2003   01dec2003 |
7. | 01 December 2004   01dec2004 |
8. |    01 April 2005   01apr2005 |
9. |   01 August 2005   01aug2005 |
10. |   01 August 2006   01aug2006 |
  |------------------------------|
11. |   01 August 2007   01aug2007 |
12. |    01 April 2008   01apr2008 |
13. |   01 August 2008   01aug2008 |
  +------------------------------+

.







lschoele@rumms.uni-mannheim.de wrote:

Hello Statalist,

I am using Stata for event study. I entered all my variables and observations. Regarding my variable "date" I have a problem. When I use "sort date", stata
sorts the date shown above:date
01 April 2002
01 April 2003
01 April 2004
01 April 2005
01 April 2008
01 August 2000
01 August 2001
01 August 2002
01 August 2003
01 August 2005
01 August 2006
01 August 2007
01 August 2008
01 December 2000
01 December 2003
01 December 2004
01 December 2005
01 December 2006
01 February 2000
01 February 2001
01 February 2002
01 February 2005
01 February 2006
01 February 2007
01 February 2008
01 July 2002
01 July 2003
01 July 2004
01 July 2005
01 July 2008
01 June 2000
01 June 2001
01 June 2004
01 June 2005
01 June 2006
01 June 2007
01 March 2000
01 March 2001
01 March 2002
01 March 2004
01 March 2005
01 March 2006
01 March 2007
01 May 2000
01 May 2001

I can tell that stata sorts by the first letter of the month. Do I have to use
a special format for the date? I also tried  the  format  01.04.2002, but that
gives me the same sortation  shown  above.

Can anyone help me?

Best regards
Lisa


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