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

[Nick Cox <njcoxstata@gmail.com>]

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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