Re: st: generate variable versus define scalar, with conditional statement

[annoporci <annoporci@gmail.com>]

> Or, he can check if each date occurs at most once,
> and simplify his code.
> 	bys date : assert _n == 1
> 	summ  open if date == mdy(1,2,2001), meanonly
> 	scalar newscalar = r(mean)

In the present case, date is a unique identifier, but this is a great  
addition to my toolkit:

bys date : assert _n == 1

Thanks Paul, I appreciate your feedback very much,

Patrick

---
Patrick Toche.



On Wed, 16 Jan 2013 19:44:55 +0800, Seed, Paul <paul.seed@kcl.ac.uk> wrote:

> Dear Statalist,
>
> It appears that what Patrick Toche wants is not something that
> Stata can do in a single command.  This is because what he wants
> is not completely clear.
>
> He wants for the system dataset -sp500- to produce a scalar that gives
> the value of a particular variable (-open-) at a particular date
> chosen by him (-date-).
>
> Depending on the data set , this is an ambiguous request.  Suppose the  
> date
> in question occurs more than once, with different values of -open-  
> attached.
> [It doesn't in this case, but it could easily do].
> Does he want the minimum, the maximum, the average, or a missing value?
>
> The following covers all these options.
>
> 	clear all
> 	sysuse sp500
>
> 	summ  open if date == mdy(1,2,2001), meanonly
> /// the meanonly option suppresses output, and saves computer time
> ///by not calculating the standard deviation.  It is not essential.
> 	scalar newscalar_mean = r(mean)
> 	scalar newscalar_min= r(min)
> 	scalar newscalar_max= r(max)
> 	if r(n) == 1 scalar newscalar = r(mean)
>
> Or, he can check if each date occurs at most once,
> and simplify his code.
> 	bys date : assert _n == 1
> 	summ  open if date == mdy(1,2,2001), meanonly
> 	scalar newscalar = r(mean)
>
> BW
>
> Paul T Seed, Senior Lecturer in Medical Statistics,
> Division of Women's Health, King's College London
> Women's Health Academic Centre, King's Health Partners
> (+44) (0) 20 7188 3642.
>
>
>
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--
Patrick Toche.
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