Re: st: replacing missing time period data with next closest period

[Jieyu Wang <joygoforward@gmail.com>]

Here is an example you may want to look at:
 (this example replace current observation with previous period if it
is in the middle)

**********************
clear

set obs 24
generate str10 state="Texas"
replace  state="New york" in 13/24
bysort state: generate month=_n
generate option=.
replace option=1 in 1
replace option=0 in 2
replace option=0 in 5
replace option=1 in 10
replace option=1 in 14/15
replace option=0 in 19/20
//prepare the data

list

sort state month

bysort state: generate nomissing=_n if ! missing(option)

generate flagbefore=nomissing
bysort state: replace flagbefore=flagbefore[_n-1] if missing(flagbefore)


bysort state: generate flaginverse=13-month
sort state flaginverse
generate flagafter=nomissing
bysort state: replace flagafter=flagafter[_n-1] if missing(flagafter)

drop flaginverse
sort state month
list

bysort state: egen min=min(flagbefore)
bysort state: egen max=max(flagafter)
replace flagbefore=min if missing(flagbefore)
replace flagafter=max if missing(flagafter)
//generate flagbefore and flagafter to indicate the nearest nonmissing index

sort state month
list

bysort state: replace option=cond( _n-flagbefore[_n]>flagafter-_n  ,
option[flagafter[_n]], option[flagbefore[_n]] )
 list
 //replace within closest period

***********************

2011/3/16 Doug Hess <douglasrhess@gmail.com>:
> Hi.
>
> I'm hoping there are a set of commands that will help me edit cells
> for this missing data problem.
>
> Each row in my dataset is a month for each state (and DC) over five
> years (i.e., 51x5x12= 3,060 rows). The columns are binary values for
> the reported presence of a policy that some states in some months have
> implemented and others have not. Unfortunately, the months in which
> states report the existence (or not) of the policy option varies by
> year, and only the months when the option is reported have been coded.
>
> Thus, a state that reports not having selected a policy option in
> April 2001 and then reports adopting the policy in August 2001, with
> no reports in between, would have the value of 0 for April and 1 for
> August, but missing "." for the other 10 months of the year (i.e.,
> missing until the next report).
>
> I would like to fill in the months in between reports with the value
> of the next closest month that has a value, and default to zero if the
>  missing month is equidistant to a 0 or 1. I.e., in the example above,
> assuming the policy had not changed before or after these reported
> months, the cells from January thru June = 0, July thru December= 1.
>
> I'm starting to think I'll just do this by hand, but I wonder if
> there's some nifty "if then...do" routine that can be created as I
> would like to add more years and do this for a large number of policy
> variables.
>
> If it matters: I'm using Stata 11 and don't have Stata programming
> language experience (as opposed to issuing commands). My computer
> programming skills stopped circa 1982 when I learned Basic on an Apple
> IIe. So, if there's a choice between clunky commands and elegant
> programming with the same results, I might go for the clunky commands.
> But I am happy to learn if there's a resource I need to consult to
> understand any advice or tips that are provided.
>
> Thank you.
>
> Doug
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