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Re: st: Stata date


From   Nick Cox <njcoxstata@gmail.com>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Stata date
Date   Tue, 9 Apr 2013 17:37:47 +0100

It's a good answer. However, -summarize- is just being a robot here.
Consider this
dopey example:

. sysuse auto
. format mpg %td

. codebook mpg

-----------------------------------------------------------------------------------------
mpg
     Mileage (mpg)
-----------------------------------------------------------------------------------------

                  type:  numeric daily date (int)

                 range:  [12,41]                      units:  1
       or equivalently:  [13jan1960,11feb1960]        units:  days
         unique values:  21                       missing .:  0/74

                  mean:   21.2973 = 22jan1960 (+ 7 hours)
              std. dev:    5.7855

           percentiles:        10%       25%       50%       75%       90%
                                14        18        20        25        29
                         15jan1960 19jan1960 21jan1960 26jan1960 30jan1960

. su mpg, format

    Variable |       Obs        Mean    Std. Dev.       Min        Max
-------------+--------------------------------------------------------
         mpg |        74   22jan1960   06jan1960  13jan1960  11feb1960

If -mpg- is a daily date, then the mean, min and max are too. However,
the standard deviation of a daily date is not itself a daily date, as
it is a number in days, regardless of the date scale. That is why I
prefer -codebook- here.

Nick
njcoxstata@gmail.com


On 9 April 2013 17:31, Rebecca Pope <rebecca.a.pope@gmail.com> wrote:
> Ray,
> See -help summarize-. You'll notice that the -format- option will
> cause the results to be displayed using the same format as the
> variable, in your case %td.
>
> Regards,
> Rebecca
>
> On Tue, Apr 9, 2013 at 11:22 AM, Ray Hawkins <sylviantas@gmail.com> wrote:
>> Hi,
>>
>> My date is stored in %td format, e.g.,
>>
>> mydate
>> 19aug2005
>>
>> When I summarize mydate:
>>
>> sum mydate
>>
>> it produces results like the following.
>>
>>     Variable |       Obs        Mean    Std. Dev.       Min        Max
>> -------------+--------------------------------------------------------
>>        buydt |   9261737    16785.61    9.022221      16771      16801
>>
>> Can I display the summary results in a specific format such as %td? This is
>> because the data is too big and sorting takes long time to see the min and
>> max dates. Or, is there a table that matches numbers to actual dates? The
>> help file says that:
>>
>> %td dates 01jan0100 to 31dec9999 (integers -679,350 to 2,936,549)
>>
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