Re: st: conditional merging

[Jeph Herrin <stata@spandrel.net>]

how about:

 u sales, clear
 merge 1:m home_id using condition
 gen lag = sale_year-inspection_year
 bys id_home : egen minimum_lag=min(lag)
 gen sale_condition if lag==minimum_lag & lag>=0
 bys home_id (sale_condition) : keep if _n==1

?
this should keep one record per home_id, with closest inspection_year 
prior to the sale date and the corresponding sale_condition.

hth,
jeph

On 11/6/2012 2:33 PM, Ben Hoen wrote:
> I have two files sales.dta and condition.dta.  sales.dta has two variables
> (home_id saleyear), and condition.dta has three variables (home_id
> inspection_year condition).  The variable inspection_year can take the vales
> of 2000-2011 for any home but for many homes only some years are present (in
> many years the home was not inspected. Therefore a sample of the data might
> look like:
>
> home_id	inspection_year	condition
> 50121		2002			4
> 50121		2006			4
> 50121		2011			3
> 50681		2004			2
> 50681		2010			3
> 51040		2006			2
> 51040		2010			2
> 51040		2011			3
>
> I would like to populate the sales.dta file with the condition of the parcel
> in the inspection_year that is the closest to, but not following the
> sale_year.
>
> So, for example, the following dataset would result
>
> home_id	sale_year	condition
> 50121		2007		4
> 50121		2011		3
> 50681		2008		2
> 51040		2003		.
> 51040		2010		3
>
> I know I am not the first person to have this problem, but could not find
> threads on this.  Maybe I am using the wrong search terms.  Any help would
> be greatly appreciated.
>
> (As I wrote this I realized one not as elegant work-around would be to
> fill-in missing data for each missing year in the condition.dta file,
> potentially using the user-written "carryforward" or even imputing the data
> using, e.g., mi impute, and then matching home_id sale_year to home_id
> inspection_year.)
>
> Thanks, in advance!
>
> Ben Hoen
> Principal Research Associate
> Lawrence Berkeley National Laboratory
> Office: 845-758-1896
> Cell: 718-812-7589
> bhoen@lbl.gov
> http://emp.lbl.gov/staff/ben-hoen
>
> Visit our publications at:
> http://emp.lbl.gov/publications
>
>
>
>
>
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