Re: st: test the format isdate

[Nick Cox <njcoxstata@gmail.com>]

As Stata's documentation clearly implies, dates are not a variable,
data or storage type. So, no check for a date type is possible. That's
why there is no -confirm date-.

Being a date is in the mind of the user and in a strong sense nothing
to do with Stata as such. I could go with

sysuse auto
format mpg %td

and Stata would not complain. That would be perverse, but not illegal.
Nevertheless the usual assumption is that a date format is diagnostic
of something you (should) understand as a date. That could easily
break down with yearly dates as often users would be entirely happy
with default formats.

I have encountered users with personal or even institutional
conventions that dates are distinguishable (indeed, _must_ be
distinguished) using some convention for variable names (e.g. that
dates and only dates have names beginning with "d"), but while such a
convention makes date management easier for such users it manifestly
has no general force.

-ds- identifies variables with date formats using one command line. I
am not clear why you appear to regard that as a poor solution.

I don't know of an -isdate- or equivalent command, but if such existed
you would be able to find it. One such is easily programmable, but my
own stance here is that writing such a program would be a waste of
time given the existence of more general tools.

In terms of your code, that can be shrunk from

qui ds, has(format %td*) // or qui findname, format(%td*)
local test "`r(varlist)'"
foreach v of varlist `test' {
        tostring `v', replace usedisplayformat force
}

to

qui ds, has(format %td*) // or qui findname, format(%td*)
tostring `r(varlist)', replace usedisplayformat force

as -tostring- takes a varlist as argument (removing the need for a
loop) and there is no need to put r(varlist) into a local macro when
it already has such a persona, as your code already illustrates.

Your code, however, is dangerous in replacing variables with -force-
so that if there is a problem with the data you may have lost
information. String date variables are not much use in Stata but your
motive in doing this may be (e.g.) export to other software.

Nick
njcoxstata@gmail.com


On 17 December 2013 14:03, rasool.bux <rasool.bux@aku.edu> wrote:
> Dear Nick,
>
> Thanks for reply, and I have used it as follows:
> *****************
>   qui ds, has(format %td*) // or qui findname, format(%td*)
>   local test "`r(varlist)'"
>   foreach v of varlist `test' {
>         tostring `v', replace usedisplayformat force
>   }
> ******************
> May be there is another good way. I have checked -confirm- command also but (confirm date variable `v') is not working. I have seen that macro at this link: http://www.stata.com/statalist/archive/2008-04/msg00892.html.
>
> Kindly let me know if there is any command like it for checking type & format of a variable i.e. -isnumber/ isdate/ isstring.
>
> Thanks & best regards
> Rasool Bux
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
> Sent: Monday, December 16, 2013 7:41 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: test the format isdate
>
> way to think more generally, as dates are typically defined only by their display formats.
>
> ds, has(format %d*)
>
> or
>
> ds, has(format %td*)
>
> would be simple examples.
>
> -findname- (SJ) is of the same flavour, but more versatile.
>
> Note that -tostring- is a Stata command, not a Stata function.
> -isnumeric- (origin not explained by you) is presumably a Stata command, not a Stata macro. Using terminology from outside Stata is likely to confuse or bemuse.
>
> All that said, -tostring- won't usefully save numeric date variables as string dates, unless you specify a date format.
> Nick
> njcoxstata@gmail.com
>
>
> On 16 December 2013 14:06, rasool.bux <rasool.bux@aku.edu> wrote:
>> Dear Statalist,
>>
>> I want to test the format of a variable in a program for conversion to string in a loop using the tostring function. If the format of a variable is %td then I want to save it in a string variable by using the tostring function.
>>
>> I have searched web I found the macro -isnumeric- . But I want to test
>> the format also i.e. -isdate-
>>
>> Kindly suggest me in this regard.
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