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From |
Jacob Wegelin <jacob.wegelin@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: can one program a function in Stata? |

Date |
Wed, 22 Apr 2009 12:21:33 -0400 |

I am about to order Kit Baum's Introduction to Stata Programming. But I'm curious whether his book will answer the following question. Stata has what I would call plain old functions, of which sqrt() is an example: . di sqrt(3.1415926535) 1.7724539 . sysuse auto, clear (1978 Automobile Data) . gen sqrtTurn=sqrt(turn) But suppose I want to define a function that's not found under -help functions-. The following approach (with a hypothetical nonstandard function) seems clumsy: capture program drop myownfunction program define myownfunction, rclass if `1' > 3 { return scalar myanswer= (sqrt(`1') + 5)^(2/3) } else { return scalar myanswer= (sqrt(`1') + 9)^(2/3) } end myownfunction 3.1415926535 di r(myanswer) Besides the awkward business of having to first call the function, then refer to - r(myanswer) - , this program only works for a single number (a scalar in the mathematical not Stata sense). If I want to apply it to an entire column of numbers (a Stata numeric variable), I'd have to write a different function, then always remember whether to call the scalar or the vector (variable) version. On the other hand, we can use sqrt() directly for either purpose. Thus, is there a way to define -myownfunction()- so that one can call it just as one calls sqrt()? Does one do this with -mata-, or ...? Would Kit Baum's book talk about this? Thanks for any insights Jacob A. Wegelin Assistant Professor Department of Biostatistics Virginia Commonwealth University 730 East Broad Street Room 3006 P. O. Box 980032 Richmond VA 23298-0032 U.S.A. E-mail: jwegelin@vcu.edu URL: http://www.people.vcu.edu/~jwegelin * * 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/

**Follow-Ups**:**st: RE: can one program a function in Stata?***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**st: AW: can one program a function in Stata?***From:*"Martin Weiss" <martin.weiss1@gmx.de>

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