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Re: st: Float Precision


From   Maarten Buis <maartenlbuis@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Float Precision
Date   Wed, 22 Aug 2012 11:36:30 +0200

On Wed, Aug 22, 2012 at 11:16 AM, Jamie Madden wrote:
> For example if we look at (using Stata 12)
>
>   sysuse auto, clear
>
> at the first row and column "gear_ratio", the value appears to be 3.58
> when in reality when you click on it, it is 3.579999. I understand the
> reasoning behind this and understand if I want to create a variable
> for example that is greater than or equal to 3.58 I should type
>
> gen newvariable=1 if gear_ratio>=float(3.58)
>
> Surely there is no need to type float for every variable that you
> create in a dataset? Is there a way to set this up for your whole
> dataset? Or change the default setting?


Generally I would only use such checks for exact equality for
integers, as computers can hold integers exactly. Sometimes you can
turn a seemingly non-integer variable into an integer variable, for
example by storing sums of money in cents rather than euros (fill in
your local currency as required). If you really believe that exact
equality is relevant to your problem than I suspect that in most cases
your variables are really similar "integers in disguise", and you can
use the same trick.

Hope this helps,
Maarten

---------------------------------
Maarten L. Buis
WZB
Reichpietschufer 50
10785 Berlin
Germany

http://www.maartenbuis.nl
---------------------------------
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