Re: st: Error with -round()-

[Jeph Herrin <info@flyingbuttress.net>]

Or, for a solution that will extend to string variables as well:

 local value=string(.8125,"%3.2f")
 di "`value'"

Eg, you can use this to do things like

 gen str4 value=string(var1,"%3.2f")

when needed.

hth,
Jeph



On 3/9/2014 4:26 AM, Nick Cox wrote:
> There is no bug here, merely a surprise if you don't understand what
> is going on. In fact, this is probably the most reported bug that is
> just a surprise at first sight in the history of Stata. I'd estimate
> reports on Statalist that are of the order of one hundred over several
> years.
>
> . local value = round(.8125,.01)
>
> . di "`value'"
> .8100000000000001
>
> . di `value'
> .81
>
> In the first example, you are seeing the decimal approximation to a
> binary approximation to .81. A little thought shows that .81, although
> a simple decimal, doesn't have an exact binary equivalent, but Stata
> does the best it can.
>
> When you insist on -display- as a string Stata is as literal as it knows.
>
> In the second example, -display-'s role is to display nicely and the
> default numeric format is sufficient to round off the minute detail.
>
> The positive answer, although it may seem paradoxical at first sight,
> is that in Stata rounding of fractions is a string manipulation, not a
> numeric manipulation.  (Rounding to integers is safe either way, as
> integers within Stata's limits clearly can be held exactly as binaries
> and as decimals.)
>
> local value : di %3.2f .8125
> di "`value'"
>
> di "`: di %3.2f .8125"
>
> are ways to ensure the correct result.
>
> For much, much more -search precision- and home in on William Gould's
> blog posts, the manual entries and three Stata Journal papers on this
> subject.
>
> Nick
> njcoxstata@gmail.com
>
>
> On 9 March 2014 02:46, Matt Vivier <mvivier@remedypartners.com> wrote:
> > Hello all,
> >
> > I'm using:
> > Stata/IC 12.1 for Windows (64-bit x86-64)
> > Revision 06 Feb 2012
> >
> > I'm very hesitant to suggest that there is a bug in Stata itself, but
> > I am getting an unexpected result when using -round()- on some
> > numbers, and have been unable to find an explanation for it.
> >
> > I'm pulling information out of my dataset, and writing it to a table
> > in an HTML file, and wanted to round the values down to something of
> > reasonable length. The vast majority of the time, -round()- functions
> > as expected, but it occasionally seems to misfire.
> >
> > This can be replicated with:
> > local value = round(.8125,.01)
> > di "`value'"
> >
> > However, if you type
> > di `value'
> >
> > You see the expected result.
> > Unfortunately, (I believe) I have to enclose it in quotes to write it
> > to the HTML file as such:
> > file write html `"<TD>`value'</TD>"'
> >
> > My questions are:
> > Can anyone replicate this issue?
> > If so, any thoughts on what causes it? It seems to be caught up in
> > treating `value' like a string due to the quotes.
> > Any thoughts on a workaround?
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