Re: st: Problem with datetime functions

[Nick Cox <njcoxstata@gmail.com>]

This seems confused on several levels.

The help for -dates and times- has explicit advice about data types  
for dates. It's a pity if people don't read it, but there you go.

The display format is no more than that, a display format, and  
immaterial to merging of any kind. For linking with other software the  
most important predictable problem is the date origin, i.e. the  
calendar date which is integer zero.

 Also, Stata has no date types as such: in practice, numeric  
variables may be assigned date formats, but that's it.

On 11 Jun 2013, at 19:43, George Vega Yon <g.vegayon@gmail.com> wrote:

> Dear Nick,
>
> Thank you for your answer. Good tip on using double when working with
> dates and times, though, at least to me, it does make sense that stata
> warns you (or something) in this type of operations. For most of the
> people who I know that uses stata, data type distinction (float, long
> or double) isn't straightforward.
>
> I need to generate a new variable because, I merge this dataset with
> another one which has a "date" variable as integer (and not as stata
> date-time "data type"). Even when I prefer working with calendar
> variables, almost all of the data sets in my work work with YYYYMMDD
> integer format.
>
> Best regards!,
>
> George Vega Yon
> 7 647 2552
> http://cl.linkedin.com/in/georgevegayon
>
> 2013/6/11 Nick Cox <njcoxstata@gmail.com>:
>
> It's not a bug in Stata. It's yours.
>
> On your -generate- you need a data type other than -float- to hold
> every digit exactly. -long- should work, but whenever dates and times
> are mentioned, thinking -double- is safe.
>
> -tostring, force- shows that you knowingly run risks of damaging the  
> data.
>
> But why -generate- a new variable? Use the display format  %tdCYND
>
> clonevar myday2 = myday
> format myday2 %tdCYND
>
> is a better way to proceed if you really need a new variable.
>
> Nick
> njcoxstata@gmail.com
>
>
> On 11 June 2013 15:18, George Vega Yon <g.vegayon@gmail.com> wrote:
> > Dear list members,
> >
> > I'm facing a problem while generating an integer from day-time
> > variable. In short, what I (in stata %td format) have is
> >
> > myday
> > 01jan2002
> > 02jan2002
> > 03jan2002
> > 04jan2002
> > ...
> >
> > What I want is
> >
> > myday2
> > 20020101
> > 20020102
> > 20020103
> > 20020104
> > ...
> >
> > Which is I though I could generate by:
> >
> > gen myday2 = year(myday)*10000 + month(myday)*100 + day(myday)
> >
> > But acctually returns
> >
> > myday2
> > 20020100
> > 20020102
> > 20020104
> > 20020104
> >
> > So, it seems that stata is rounding my new variable. I don't want to
> > say that this is a bug, but what are the alternatives?.
> >
> > I've solve this with:
> >
> > format %tdCCYYNNDD myday
> > tostring myday, u gen(myday2) force
> > destring myday2, replace
> >
> > myday2
> > 20020101
> > 20020102
> > 20020103
> > 20020104
> >
> > But still, stata rounding my integers doesn't sound very good. Any  
> > ideas?
> >
> > Thanks!
> >
> > George Vega
> >
> > PS: Running on windows 7
> > c(stata_version) = 12.1
> > c(version) = 12.1
> > c(born_date) = "18 Dec 2012"
> > c(flavor) = "IC"
> > c(os) = "Windows"
> > c(osdtl) = "64-bit"
> > c(machine_type) = "PC (64-bit x86-64)"
> > c(byteorder) = "lohi"
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