Re: st: Re: Retrieving a master dataset after merging

["Michael Blasnik" <michael.blasnik@verizon.net>]

Good points, and obviously it would be best not to destroy your master 
dataset to begin with so that you could start from scratch.  However, I 
think that in most situations you can recover the original master dataset:

1) one-to-one merge: just follow my original email suggestion of -drop if 
_merge==2-, -drop _merge-, -drop usingonlyvarlist-

2)  one-to-many merge, do the same as (1) and then -bysort mergevarlist: 
keep if _n==1-

3) many-to-one merge:  same solution as one-to-one merge

4) many-to-many merge -- are most likely unfixable, but you should never do 
this type of merge, although it could occur accidentally if you are sloppy

So, with the exception of many-to-many merges, you can retrieve the master 
dataset if you need to.

Michael Blasnik
michael.blasnik@verizon.net


----- Original Message ----- 
From: <pec187@abdn.ac.uk>
To: <statalist@hsphsun2.harvard.edu>
Sent: Sunday, April 10, 2005 7:33 AM
Subject: Re: st: Re: Retrieving a master dataset after merging



> Also assuming that it's a one-to-one merge - if not the number of
> observations would have increased.  Also assuming that the OP has
> specified the merge correctly - again the number of observations might
> have increased if there's more than one merge in the -using- data.
>
> I think it's best to start from scratch.
>
>
>
> > Well, I don't think you should ever save the new merged dataset on top of
> > the master (i.e., don't use -save, replace-).  If you follow this advice
> > then you could just -use master-.  Assuming you didn't follow this 
> > advice,
> > you can retrieve the master dataset (if you didn't specify -update- as an
> > option).  Just type:
> >
> > keep if _merge==1 | _merge==3
> > drop _merge
> >
> > if the using dataset contains some variables not in the master dataset,
> > you
> > then drop those:
> >
> > drop usingvar1 usingvar2 usingvar3...
> >
> > Michael Blasnik
> > michael.blasnik@verizon.net
> >
> > ----- Original Message -----
> > From: "louis boakye-yiadom" <louisby@hotmail.com>
> > To: <statalist@hsphsun2.harvard.edu>
> > Sent: Saturday, April 09, 2005 12:24 PM
> > Subject: st: Retrieving a master dataset after merging
> >
> >
> >
> > > Dear All,
> > > After doing a -merge-, can one retrieve the master dataset? If yes, how
> > > can it be done? Thank you.
> > >
> > > Louis
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