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From |
Rijo John <rmjohn@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Re: Data Management |

Date |
Wed, 15 Apr 2009 11:32:23 -0500 |

Thanks Mike. Your formula did the job. The change variable I listed here doesnt give the number of years since the last change in P_t because the years are not continuous. In the actual data, I have all the years present and there is no lose of continuity. Thanks, Rijo. On Wed, Apr 15, 2009 at 11:23 AM, Mike Kim <argonomos@gmail.com> wrote: > Hi Rijo, > > This should do it: > bys id p_t (year): gen change=_n-1 > > However your question is not clear. The two examples are different. You also > said that change is the number of years passed since the last change in P_t, > but Change as you wrote is not this one. > > Mike. > > > ----- Original Message ----- > From: "Rijo John" <rmjohn@gmail.com> > To: "stata" <statalist@hsphsun2.harvard.edu> > Sent: Wednesday, April 15, 2009 11:07 AM > Subject: st: Data Management > > > Hi, > > I have a time series data set as follows. > > ID year P_t-1 P_t > 1 1990 16 16 > 1 1991 16 16 > 1 1996 16 16 > 1 2005 42 42 > 1 2006 42 42 > 1 2007 42 42 > 2 1990 29 29 > 2 1991 29 29 > 2 1992 29 29 > > Where P_t and P_t-1 represents price in year t and t-1 respectively. > What I wish to achieve is to create a new variable "Change". This > variable should show the number of years passed since the last change > in P_t. In the above example the data should finally look like below. > > ID year P_t-1 P_t Change > 1 1990 . 16 0 > 1 1991 16 16 1 > 1 1996 16 16 2 > 1 1997 16 16 3 > 1 2005 16 42 0 > 1 2006 42 42 1 > 1 2007 42 42 2 > 2 1990 . 29 0 > 2 1991 29 29 1 > 2 1992 29 29 2 > 2 1993 29 35 0 > > > If I do > > bysort ID P_t : gen Change=_n-1 I get the varible numbered but it > doesnt sort the year. If I sort ID and year then I cant use the _n to > generate these numbers. > Can someone help me with this? > > Thanks in advance, > > Rijo. > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > -- Rijo M John, PhD Institute for Health Research and Policy (MC 275), 1747 West Roosevelt Road, Room 558, Chicago, Illinois 60608. Ph: 312-413-9057 Fax: 312-355-2801 URL: http://ihrp-web.ihrp.uic.edu/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: Data Management***From:*Rijo John <rmjohn@gmail.com>

**st: Re: Data Management***From:*"Mike Kim" <argonomos@gmail.com>

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