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From |
mario fiorini <mariofiorini73@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: problem with `r(min)' and `r(mean)' macros |

Date |
Mon, 28 Jan 2013 16:14:24 +0100 |

thanks Nick, I could sense it was a precision issue, but I was very confused because it was only there for `r(min)' and not `r(max)'. [and sorry for the obviously stupid `r(mean)' check]. now I understand both precision issues. Mario On 28 January 2013 16:01, Nick Cox <njcoxstata@gmail.com> wrote: > This is a precision issue, biting you twice over. > > First off, there is a loss of precision possible with using e.g. > `r(min)' rather than r(min) which is roughly parallel to the lower > precision of macros compared with scalars. > > !!! Don't use local macros if you seek maximum precision with non-integers. !!! > > Second, testing for exact equality can be tricky at the best of times > for reasons often rehearsed on this list and elsewhere. > > . search precision > > in an up-to-date Stata and start with Bill Gould's blog postings. > > Try this instead: > > set obs 1000 > gen var1 = runiform() > su var1 > scalar max = r(max) > scalar min = r(min) > count if var1 == max > count if var1 == min > > Whether the mean of random numbers on the unit interval is equal to > any particular random number is surely of less interest. > > Nick > > > On Mon, Jan 28, 2013 at 2:47 PM, mario fiorini <mariofiorini73@gmail.com> wrote: >> Dear statalist, >> I am summarising a variable and then trying to use the `r(.)' macros >> However, in some instances Stata does not seem to find any variables >> that take the `r(min)' and `r(mean)' values. For some reason, it does >> work with `r(max)' instead. >> The code below should clarify the problem. When I run it, I always get >> that no observation takes the min or the mean (why???), but there is >> an observation that takes the max. >> The problem does not depend on whether I use the original `r(min)' or >> a macro=`r(min)'. >> If it matters I am using a mac osx 10.8 with Stata 12.1 MP. >> Any hint would be appreciated because it is driving me crazy. >> Mario >> >> // Start >> clear >> set obs 1000 >> ge id = _n >> ge var1 = uniform() >> su var1 >> local LCmin =`r(min)' >> local LCmean =`r(mean)' >> local LCmax =`r(max)' >> >> count if var1==`LCmin' >> count if var1==`LCmean' >> count if var1==`LCmax' >> // Ends > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/faqs/resources/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/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: problem with `r(min)' and `r(mean)' macros***From:*Nick Cox <njcoxstata@gmail.com>

**References**:**st: problem with `r(min)' and `r(mean)' macros***From:*mario fiorini <mariofiorini73@gmail.com>

**Re: st: problem with `r(min)' and `r(mean)' macros***From:*Nick Cox <njcoxstata@gmail.com>

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