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From |
"Martin Weiss" <martin.weiss1@gmx.de> |

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 14:53:45 +0200 |

Use -help f_float- instead of -round-, as explained in http://www.stata.com/support/faqs/data/float.html HTH Martin -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Naunihal Singh Sent: Friday, October 24, 2008 1:58 AM To: statalist@hsphsun2.harvard.edu Subject: st: Re: Problem with replace if - test condition works only for some values of test variable 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? Thanking you all in advance, and Phil for his earlier response, N On Thu, Oct 23, 2008 at 6:32 PM, Naunihal Singh <naunihal@post.harvard.edu> wrote: > Please, indulge me. I'm sure I've overlooked something basic, but > replace if is working only for certain values of the test variable and > not for others. > > Start with any dataset open > Here is the code fragment that replicates my problem: > > ge y=. > generate x= (_n/100)-0.01 in 1/101 > replace y=1 if x==0 > replace y=1 if x==.01 > replace y=1 if x==.25 > replace y=1 if x==.26 > replace y=1 if x==.5 > replace y=1 if x==.51 > replace y=1 if x==.75 > replace y=1 if x==.76 > replace y=1 if x==1 > replace y=1 if x==.99 > > I'm able to make assignments to y only when x equals 0, .25, .5, .75, > and 1 but for no other value. This is the output I get: > > . replace y=1 if x==.5 > (1 real change made) > > . replace y=1 if x==.51 > (0 real changes made) > > Why does this happen and how do I fix it? x is a float, so it should > have enough precision for the test condition. And if the test can > recognize .25 it should be able to recognize .26. > > Thanks > > N > * * 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/ * * 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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