Re: st: RE: what command to keep firms-years with multiple occurrence of only one type of events

[Robert Picard <picard@netbox.com>]

Another way:

bys Firm Year (Event): keep if (Event[1]==Event[_N]) & Event==3

Robert

On Fri, Sep 27, 2013 at 9:29 AM, Joe Canner <jcanner1@jhmi.edu> wrote:
> Nahla.
>
> If your Event variable is numeric, this should work:
>
> . bys Firm Year: egen mn=mean(Event)
> . bys Firm Year: egen sd=sd(Event)
> . keep if mn==3 & sd==0
>
> This is, admittedly, a little unconventional, but should be pretty efficient.
>
> Regards,
> Joe Canner
> Johns Hopkins University School of Medicine
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nahla Betelmal
> Sent: Friday, September 27, 2013 4:43 AM
> To: statalist@hsphsun2.harvard.edu
> Subject: st: what command to keep firms-years with multiple occurrence of only one type of events
>
> Dear Statalist members,
>
> It would be great if you can let me know what command I can use to keep firms-years with multiple occurrence of only one type of events in my data.
>
> I have firms-years-events data set. A firm can have multiple entries for the same year if it undertakes certain corporate events . I coded the events as 1,2,3, 4. For example the data looks like this
>
>
> Firm   Year    Event
> A        1994       2
> A        1994       3
> A        1994       3
> A        1995       1
> A         1995      3
> A         1996       2
> A         1996       4
> A         1996       3
> A          1997       3
> A           1997      3
> A           1998       1
> A            1998       1
> B
> ..
>
>
> I am only interested in studying firm-years where  only event 3 was undertaken (i.e. keep both entries for year 1997 only). In other words, I want to drop firm years where there are a mix of events shown as multiple entries/observations ( years 1994, 1995, 1996) and multiple unique occurrence of event other than 3 (year 1998).
>
> I understand that I can do it on two stages, first drop  firm-years with mix events, then second stage drop years with unique events other than 3.
>
> the problem that I  don't know what command should I use to do the first stage ( drop firms-years with multiple entries of multiple events).
>
> Thank you in advance, I highly appreciate your kind help
>
> Nahla Betelmal
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