Re: st: converting series of dates to numeric variable

[Nick Cox <njcoxstata@gmail.com>]

But you need to check that your dates really are equally spaced. You
can use -mod(,)- for that purpose.

. di mod(date("1 Nov 2009", "DMY"), 28)
2

. di mod(date("29 Nov 2009", "DMY"), 28)
2

All equally spaced dates have the same remainder.

For more on -mod(,)- see

SJ-7-1  pr0031  . Stata tip 43: Remainders, selections, sequences, extractions
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
        Q1/07   SJ 7(1):143--145                                 (no commands)
        tip for uses of the modulus

For more on -floor()- and -ceil()- see

SJ-3-4  dm0002  . . . . . . . . Stata tip 2: Building with floors and ceilings
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
        Q4/03   SJ 3(4):446--447                                 (no commands)
        tips for using floor() and ceil()

Nick

On Wed, May 23, 2012 at 10:19 AM, Nick Cox <njcoxstata@gmail.com> wrote:
> Yes, it should be mildly alarming, as it shows that you are trying
> something which is inappropriate for you. But you can fix that.
>
> The -date()- function converts to daily dates. That is its job. In
> terms of daily dates, the resolution of your data (delta) is one day
> and you have (lots of) gaps. Stata doesn't look out for equally spaced
> dates in what it sees as gappy time series.
>
> In your case I would recommend working with -floor(edate1/28)- as a
> time variable, which gives equally spaced dates with 28 days as an
> interval. Using -int()- or -ceil()- instead of -floor()- would work as
> well. For example,
>
> . di floor(date("1 Nov 2009", "DMY")/28)
> 650
>
> . di floor(date("29 Nov 2009", "DMY")/28)
> 651
>
> So go
>
> gen edate2 = floor(edate1/28)
> tsset identif2 edate2
>
> Nick
>
> On Wed, May 23, 2012 at 10:07 AM, loggyedr salvez
> <loggyedy@googlemail.com> wrote:
>
>> I have observations every 4 weeks (4-week period data).
>>
>> In  the excel.csv file i format the cells for the date column as follows
>>
>>           dates11                     identier            variable
>>  November 1, 2009                  1
>> November 29, 2009                  1
>> December 27, 2009                  1
>> January 31, 2010                     1
>>  November 1, 2009                   2
>>  November 29, 2009                  2
>>   December 27, 2009                2
>>   January 31, 2010                   2
>>
>> and then I use the commads:
>>
>> gen edate1 = date(dates11, "MDY")
>> format edate1  %d
>>  tsset identifier edate1
>>
>>
>>
>> and I get the following stata message:
>>
>> tsset identif2 edate1
>>       panel variable:  identif2 (strongly balanced)
>>        time variable:  edate1, 02nov2008 to 09oct2011, but with gaps
>>                delta:  1 day
>>
>>
>> Is this message something alarming? why "gaps"? and why delta "1 day"

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