Jose Luis Negrin Mu�oz
> > I have used the following small program to get rid of duplicates
> >
> > sort ref;
> > by ref: gen dup=_n;
> > gsort ref -mesini dup;
> > drop if dup>1;
> >
> > where ref is a reference code and mesini is a variable
> > related to time
> > (1, 2...j); these are the variables I am sorting my data
> > by. So I will
> > keep only the oldest data with each particular reference code
>
> Two comments:
>
> 1. This code appears to keep the most recent
> observation within each group, not the oldest.
> Another way to do it is
>
> bysort ref (mesini) : keep if _n == _N
>
Jose's code needs more comment. He had
sort ref;
by ref: gen dup=_n;
gsort ref -mesini dup;
drop if dup>1;
The -gsort- makes no difference to what is dropped, so
in terms of what is kept (although not in what order)
Jose's code is just
sort ref;
by ref: gen dup=_n;
drop if dup>1;
which is equivalent to
bysort ref: drop if _n > 1
or
bysort ref : keep if _n == 1
The problem here is what is first (_n == 1) within
each group of -ref- is not guaranteed to be
the same observation, let alone the time desired.
This is what was spelled out in the examples in my
original reply to Radu.
Nick
[email protected]
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