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

[Joe Canner <jcanner1@jhmi.edu>]

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
>
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/faqs/resources/statalist-faq/
> *   http://www.ats.ucla.edu/stat/stata/

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/faqs/resources/statalist-faq/
*   http://www.ats.ucla.edu/stat/stata/

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/faqs/resources/statalist-faq/
*   http://www.ats.ucla.edu/stat/stata/