RE: st: Converting numbers to string: %f versus %g

[Joe Canner <jcanner1@jhmi.edu>]

For Stata>=10 is there a better way to do this than a combination of -date()- and -string()- (or -tostring-)?  Or is the ability of -date()- to handle run-together dates new what is new with Stata 10?

Moribund or not, for Stata>=10 users I think -todate- might still be preferable to trying to remember the correct form of -date(string())- required. (Although for large data sets I suppose there might be performance considerations.)

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
Sent: Thursday, August 22, 2013 1:37 PM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: Converting numbers to string: %f versus %g

Thanks. -todate- (SSC), however, is in essence a program dating back to 2001. Its rationale was that Stata did not (then or indeed
previously) support easy import of "run together" dates until version 10.

Moreover, -todate- does not support date-times, which again Stata didn't support until version 10.

It remains accessible for two major reasons:

1. There are people still using Stata <10.

2. If anybody's program or do file uses -todate- then the program should be accessible too.

However, it is moribund and will not be revisited by me unless someone finds a bug.
Nick
njcoxstata@gmail.com


On 22 August 2013 18:29, Joe Canner <jcanner1@jhmi.edu> wrote:
> Nick,
>
> Thanks for the caution (and the good laugh).  If nothing else, the process of reviewing and documenting this problem  will (hopefully) remind me not to use %g in the future for situations like this (and to use -todate- where applicable).
>
> Regards,
> Joe
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu 
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
> Sent: Thursday, August 22, 2013 1:03 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: Converting numbers to string: %f versus %g
>
> My impression is that %g is more complicated than you would really want documented. It tries to be as smart as possible for a great range of situations, but it's hard to predict exactly what it does.
>
> A little like the usual R stories about what "R" stands for (next to "S" but first written by a Robert and a Ross), "g" does follow "f" but also stands for Gould. Could be curious coincidence.
>
> -todate- is from SSC.
>
> Nick
> njcoxstata@gmail.com
>
>
> On 22 August 2013 17:43, Joe Canner <jcanner1@jhmi.edu> wrote:
>> Dear Stata community,
>>
>> According to the (Stata 12) help for -format-: " %g differs from %f in that (1) it decides how many digits to display to the right of the decimal point, and (2) it will switch to a %e format if the number is too large or  too small."
>>
>> However, there seem to be more differences than this.  I have a numeric (long) variable with a date in the form YYYYMMDD that I want to convert to a date variable. I did the following:
>>
>> . gen DOS=date(string(DateofService,"%8.0g"),"YMD")
>>
>> This didn't work, because the -string()- function returned the same value ("2.0e+07") regardless of the value of DateofService.  This suggests that the %g format thinks the number is too large for the format. This can be fixed with one of the following:
>
>>
>> . gen DOS=date(string(DateofService,"%10.0g"),"YMD")
>> . gen DOS=date(string(DateofService,"%8.0f"),"YMD")
>>
>> My question is this: why does %f work with the right number of digits (8), but %g only works if you overstate the number of digits?  Is the required number always two more than the actual number of digits?
>>
>> This is mostly a curiosity question, but it sometimes trips me up when I instinctively/mindlessly choose %8.0g and then wonder why my code isn't working.  I also sometimes forget the format and I wonder why -string()- can't guess the correct format, but that is another story...
>>
>> (And, yes, I recently became aware of Nick Cox's -todate- program and 
>> will probably use that from now on.)
>>
>> Thanks,
>> Joe Canner
>> Johns Hopkins University School of Medicine
>>
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