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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: Re: Problem with replace if - test condition works only for some values of test variable |

Date |
Fri, 24 Oct 2008 15:10:12 +0100 |

The precision issue is elaborated at length in several sources already referred to you. . findit precision And look at the FAQs and Stata Journal articles there listed. The key point is that deep, deep down Stata is necessarily using binary representations of decimal numbers. Some numbers can be held exactly, some can't. So for example it is not correct either that "x actually equals .2599999". A secondary point is whenever you use -display- it uses a default format, so -display- used in that way cannot be _guaranteed_ to show exactly how Stata holds numbers. Rather than recapitulating what's already been written up in detail in various places, I encourage you to read, as earlier recommended. Nick n.j.cox@ Naunihal Singh I think I understand a bit better what's going on. replace y=1 if x==.26 fails because x actually equals .2599999 . di x[27] .25999999 (this is strange b/c x was generated with this command: generate x= (_n/100)-0.01 in 1/101 ) So the problem wasn't that float had too few digits of precision (both .25 and .26 fit in the same number of bytes), it's that stata was storing (27/100)-0.01 as .25999999 instead of .26. I've tried using the round command to tackle this, but I must be doing something wrong in the syntax: replace x=round(x,0.01) (0 real changes made) even though di round(.25999999, 0.01) .26 Is there a problem with using round in replace in that way? * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: Re: Problem with replace if - test condition works only for some values of test variable***From:*Naunihal Singh <naunihal@gmail.com>

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