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From |
Ben.Kriechel@roa.unimaas.nl |

To |
statalist@hsphsun2.harvard.edu |

Subject |
RE: st: collapse (sum) versus egen (sum) |

Date |
Thu, 19 Aug 2004 16:22:08 +0200 |

Thanks Dan, I will look into it. I was also VERY surprised to see that there is a difference between the two commands. I considered them -- and I still believe they are intended -- to be equivalent. --- Ben -------------------------------------------- Ben Kriechel Research Centre for Education and the Labour Market <Ben.Kriechel@roa.unimaas.nl> -----Original Message----- From: Dan Blanchette [mailto:dan_blanchette@unc.edu] Sent: donderdag 19 augustus 2004 16:13 To: statalist@hsphsun2.harvard.edu Subject: Re: st: collapse (sum) versus egen (sum) Perhaps more information about the discrpency you noticed would be helpful? -egen- and -collapse- both use -generate-'s sum function. The only difference I see is that -collapse- generates the new variable as datatype double where -egen- let's you choose, though the default is float. If you choose a datatype that cannot handle the resulting sum, then you would end up with missing values and thus a different result than you would with -collapse-. If your sums are larger than floats maximum 1.70141173319*10^36 then you would get varying results. Try your program again choosing datatype double with -egen- to see if this fixes the problem. To view the ado files for these commands you can download -adoedit- from the SSC or: . findfile collapse.ado . view "`r(fn)'" . findfile egen.ado . view "`r(fn)'" or more specifically: . findfile _gsum.ado . view "`r(fn)'" Dan Blanchette Applications Analyst Programmer Carolina Population Center UNC-CH > While aggregating a dataset using collapse some strange results were > obtained: > > collapse (sum) aantal, by(opl114) > > Did not give the same results as the same dataset gave in other programs. > > Checking with > > egen oplantal=sum(aantal),by(opl114) > > though gave exactly the same (correct) number that other programs gave me. > Can somebody explain to me how the summation (could) differ between collapse > and egen? > > Thanks. > -------------------------------------------- > > Ben Kriechel > > Research Centre for Education > and the Labour Market > <Ben.Kriechel@roa.unimaas.nl> > > > * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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