Nemo Johnson wrote:
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I note that in another package, data can be completely subset into separate
temporary datasets without having any effect on the original. I know, of
course, that stata can do the same thing using "by" or "drop/keep", but the
logic seems different (in Stata, the "by" statements clearly need to
continually recur, and using "keep" requires great caution).
Yes of course I know this is just a taste issue, but perhaps there is a
command I'm unaware of. Any suggestions?
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Nick Cox responded:
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This question is rather general: I don't get a clear
sense of what specific flexibility you're missing.
However, Stata doesn't offer a way of doing this
as such. You can -save- parts of the data
as separate data sets, you can do things to
subsets, as you indicate, etc.
I think the return question is: what do you
want to do that you think you can't do in Stata?
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I think that Nemo wasn't saying that you couldn't subset a dataset with Stata,
but that it seemed less straightforward than with another package. Others have
mentioned the same thing. See, for example,
www.stanford.edu/class/hrp223/2002f/OtherTalks/ClinicalTrials2002.ppt ,
in particular, Slide 56 in comparison to Slides 36 and 49.
I'm not sure whether this would be a reasonable or even feasible alternative,
but with Stata Release 8 with currently updated executable and ados, you can
execute structured query language (SQL) statements to any available data source
name (DSN). See help -odbc-. Prior to this, Stata could only import from an
open database connectivity (ODBC) data source. I haven't tried it yet, so I
don't know whether it would work, but -odbc exec()- might be the basis for a
way to subset a dataset in memory to multiple temporary datasets (DSNs to a
spreadsheet or database created for the purpose) without affecting the dataset
in memory.
Joseph Coveney
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