Consider
. replace var3=var3[_n+1] if var3==. & _n<_N
The restriction _n < _N only bites with the last
value. In this example, it makes no difference,
as a reference to var3[_N+1] is evaluated as missing,
and so the restriction can be set on one side.
In words, you are asking Stata to replace missing with
the next value. Only in the case of var3[2]
does this make any difference, but Stata is
doing exactly what you asked. Perhaps the
principle being missed is given by the
title of a note by Roger Newson, one that
is also stressed in various FAQs, including
the one cited below.
SJ-4-4 dm0008 Stata tip 13: generate and replace use the current sort order
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Newson
Q4/04 SJ 4(4):484--485 (no commands)
tips for using generate and replace, which use the
current sort order
In addition what I think is your problem is discussed
at length in
FAQ . . . . . . . . . . . . . . . . . . . . . . . Replacing missing values
2/03 How can I replace missing values with previous or
following nonmissing values?
http://www.stata.com/support/faqs/data/missing.html
Nick
[email protected]
Daniel Hoechle
> Consider the following three identical variables to start with:
>
> var1 var2 var3
> . . .
> . . .
> . . .
> 2 2 2
> 3 3 3
> 4 4 4
> . . .
> . . .
> . . .
>
> Typing
>
> . replace var2=var2[_n-1] if var2==. & _n>1
> . replace var3=var3[_n+1] if var3==. & _n<_N
>
> results in
>
> var1 var2 var3
> . . .
> . . .
> . . 2
> 2 2 2
> 3 3 3
> 4 4 4
> . 4 .
> . 4 .
> . 4 .
>
>
> Why does Stata replace all three missings in the first case
> but only the
> first missing in the second case? Do I have to sort the dataset the
> other way around in order to fill var3 in a similar way as var2 or is
> there an easy workaround?
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