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RE: st: could someone pls explain me this


From   tashi lama <ltashi32@hotmail.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: could someone pls explain me this
Date   Mon, 30 Apr 2012 19:50:49 +0000

Thank you very much Nick....



----------------------------------------
> Date: Mon, 30 Apr 2012 19:33:12 +0100
> Subject: Re: st: could someone pls explain me this
> From: njcoxstata@gmail.com
> To: statalist@hsphsun2.harvard.edu
>
> You need to think of what the problem is to which this code is a solution.
>
> What is the value of a string variable corresponding to a value of a
> numeric variable? You can't say
>
> summarize <strvar> if <numvar> == #
>
> as -summarize- doesn't summarize string variables. So, you need to
> find out _where_ in the data it is true that
>
> <numvar>== #
>
> i.e. use a look-up technique. If a variable contains observation
> numbers, then r(min) and r(max) after -summarize- applied to that
> variable will also contain observation numbers.
>
> Nick
>
> On Mon, Apr 30, 2012 at 7:24 PM, tashi lama <ltashi32@hotmail.com> wrote:
> > thank you. I still have some clouds.
> >
> > 1.Why do we have to summarize the temp var?
> >
> > 2.Minimum such obs no r(min). Are we looking the minimum obs in the tempvar? Is it 3 in the following example?
> >
> >
> >
> > epcom noncom __000001 |
> > |------------------------------------------|
> > 1. | 18001 Acheres . |
> > 2. | 18002 Ainay-Le_Vieil . |
> > 3. | 18003 Les Aix -d'Angillion 3 |
> > 4. | 18004 Allogny . |
> > 5. | 18005 Allouis . |
> >
> >
> >
> >
> > 3. Could we have said instead of minimum or maximum no, non-missing obs no because there is only one obs in tempvar?
> >
> > ----------------------------------------
> >> Date: Mon, 30 Apr 2012 18:37:56 +0100
> >> Subject: Re: st: could someone pls explain me this
> >> From: njcoxstata@gmail.com
> >> To: statalist@hsphsun2.harvard.edu
> >>
> >> The code
> >>
> >> tempvar tv1
> >> gene `tv1'=_n if depcom==18003
> >> summ `tv1', meanonly
> >> local index=r(min)
> >> local mymacro=nomcom[`index']
> >> drop `tv1'
> >>
> >> is a way of looking up the value of -nomcom- when -depcom- is 18003.
> >> The temporary variable contains observation numbers for which -depcom-
> >> is 18003. A certain way of finding such an observation if any exist is
> >> to find the minimum such observation number. The maximum would do fine
> >> as an alternative. The code could be shortened
> >>
> >> tempvar tv1
> >> gene `tv1'=_n if depcom==18003
> >> summ `tv1', meanonly
> >> local mymacro=nomcom[r(min)]
> >> drop `tv1'
> >>
> >> The main point of similar code is to automate value look-up. It's
> >> usually a long-winded way to proceed if you are working interactively.
> >>
> >> Nick
> >>
> >> On Mon, Apr 30, 2012 at 6:24 PM, tashi lama <ltashi32@hotmail.com> wrote:
> >>
> >> > I am doing sth similar to what I found in archive titiled "Re: st: save the value of a string variable into a macro". I am not sure if I followed the code although it looks relatively st. forward.
> >> >
> >> >
> >> >
> >> > Here is the dataset and goal
> >> >
> >> > +-----------------------------+
> >> > | depcom nomcom |
> >> > |-----------------------------|
> >> > 1. | 18001 Acheres |
> >> > 2. | 18002 Ainay-le-Vieil |
> >> > 3. | 18003 Les Aix-d'Angillon |
> >> > 4. | 18004 Allogny |
> >> > 5. | 18005 Allouis |
> >> > +-----------------------------+
> >> >
> >> > Where depcom is an id. I want to save a specific values of the variable "nomcom" into a variable, for example, I want to obtain :
> >> > . di "`mymacro'"
> >> > Archeres
> >> >
> >> >
> >> >
> >> > The code is
> >> >
> >> >
> >> >
> >> > tempvar tv1
> >> > gene `tv1'=_n if depcom==18003
> >> > summ `tv1', meanonly
> >> > local index=r(min)
> >> > local mymacro=nomcom[`index']
> >> > drop `tv1'
> >> >
> >> >
> >> >
> >> >
> >> > I follow line 1 and 2. I am not sure why we need line 3. Line 4 established a macro which is used in line 5. But, I don't follow why the macro takes r(min) as expression. I would think the macro `index' should capture the value(the only value in fact) in tv1.
>
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