Thank you for all the suggestions. I will try all of them and report the results later.
Anupit
----- "Friedrich Huebler" <[email protected]> wrote:
> Anupit,
>
> -reshape- is indeed slow. You can change the structure of your data
> by
> saving the contents of the variables in individual files that are
> subsequently combined with -append-. The difference between the two
> approaches can be demonstrated with the auto data.
>
> First, create a dataset with 148,000 observations in 10 variables,
> plus an identifier.
>
> sysuse auto, clear
> drop make foreign
> local i = 1
> foreach var of varlist * {
> ren `var' var`i'
> local ++i
> }
> expand 2000
> gen i = _n
>
> We can now -reshape- the data from wide to long.
>
> reshape long var, i(i) j(j)
>
> The alternative solution does not rely on -reshape-. Instead, we use
> -forvalues- in combination with -preserve-, -keep-, -save-, -restore-
> and -append-.
>
> d, s
> local j = r(k) - 1
> forvalues i = 1/`j' {
> preserve
> keep i var`i'
> rename var`i' var
> gen j = `i'
> tempfile var`i'
> save `var`i''
> restore
> }
> use `var1', clear
> forvalues i = 2/`j' {
> append using `var`i''
> }
>
> -reshape- is more convenient because it only takes one line of code.
> This convenience comes at the cost of processing time and memory
> requirements. On my PC the first solution with -reshape- takes about
> 11 seconds. The second solution takes less than 2 seconds and also
> needs less memory.
>
> Friedrich
>
> On Thu, Oct 16, 2008 at 10:57 AM, Supnithadnaporn, Anupit
> <[email protected]> wrote:
> > Hello,
> >
> > Martin and Nick, thank you so much. Your suggestion works very
> well.
> >
> > I am sorry for being unclear about my question.
> > I will clarify it now. I have a large dataset around 1 million
> records. There are
> > around 20 variables. I would like to run the clogit regression,
> which requires me
> > to reshape the data into the long form. Basically, it is the model
> of a person
> > choosing a product from the choice set of 12. Thus, the total
> records would be of
> > 12 million after reshaping.
> >
> > In the beginning, I tried with the smaller sample and reshape worked
> very slow.
> > Then, I thought I should start with only 2 ID variables: person ID
> and choice ID (1-12).
> > I created the wide form data of only 2 ID variables, reshaped it to
> the long form, and
> > lastly merged other variables that are associate with person and
> choice respectively.
> >
> > However, even with the only 2 ID variables, it took a long time for
> reshape to finish
> > for the small sample of the total 1 million records. That is why I
> try to find the
> > faster way to create the empty dataset with 2 ID variables first.
> Then my next step
> > is to merge the information about a person and the choice.
> >
> > I hope this is clear enough. And if you and others have other better
> approach to
> > prepare the data like this, please let me know. There are a lot more
> for me to learn
> > from all of you.
> >
> > Thank you,
> > Anupit
> >
> >
> > ----- "Nick Cox" <[email protected]> wrote:
> >
> >> Martin's advice looks good.
> >>
> >> But Anupit's question doesn't hang together for me. The specific
> >> example, and even longer ones of the same form, don't strike me as
> >> -reshape- questions at all as they involve creating new data in
> >> structured form.
> >>
> >> By the way, for large datasets make sure to use -egen long- or
> -egen
> >> double- if you need to.
> >>
> >> But if you had a -reshape- question, strict sense, I doubt you
> could
> >> speed things up much by programming it yourself with -forvalues-
> or
> >> -foreach-. That would, broadly speaking, mean that you were a
> better
> >> Stata programmer than the Stata developers. There could well be
> >> exceptions, but I'd guess that this statement would be true much
> more
> >> often than its converse.
> >>
> >> Nick
> >> [email protected]
> >>
> >> Martin Weiss
> >>
> >> - h egen,seq()-
> >>
> >> Supnithadnaporn, Anupit
> >>
> >> Would you please suggest me how to create data in the long form
> >> by *not* using reshape? I would like to avoid reshape because
> reshape
> >> takes very very long time. In fact, the final & total number of
> >> records
> >> that I have to create would be around 12,000,000.
> >>
> >> I think foreach and forvalues can do this work.
> >> But, I am a novice in Stata programming and could not figure out
> so
> >> far.
> >>
> >> In the beginning, I have only Obsid which is created by
> >>
> >> gen Obsid = _n
> >>
> >> The desired data would look like this:
> >>
> >> Obsid Vid Imp
> >> 1 1 1
> >> 2 1 2
> >> 3 1 3
> >> 4 1 4
> >> 5 2 1
> >> 6 2 2
> >> 7 2 3
> >> 8 2 4
> >>
> >> ...
> >>
> >>
> >> 100 25 4
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