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From |
"Eva Poen" <[email protected]> |

To |
[email protected] |

Subject |
Re: st: row mean (mean across columns) |

Date |
Wed, 8 Oct 2008 20:01:59 +0100 |

Jacob, 2008/10/8 Jacob Wegelin <[email protected]>: > Given any dataset of all numeric variables, I want to generate a new > variable called myMean, which is the arithmetic mean (the average) across > all the variables. The program below solves this problem. But surely there > is a one-line command that will perform this task in Stata? > > The post http://www.stata.com/statalist/archive/2008-09/msg00597.html > appears to contain a bug, in the sense that the row total computed is not > corrected as in my code below. > > This should be done in a general manner: > > (1) As in the current dataset, the variables will not necessarily be in a > form like a1 to a100. > > (2) The number of variables is arbitrary, so I cannot hard-code the > denominator as when myMeanByHand is computed below. > > (3) If any value in a row is missing (.), the mean computed must also be > missing, since then the mean across all variables is not defined. (Thus egen > rowtotal is not the answer.) I might be misunderstanding you, but wouldn't qui ds local varlist `r(varlist)' egen miss = rowmiss(_all) egen mean = rowmean(`varlist') if miss==0 be a solution? It will calculate the average you want, in a flexible manner, but only if there are no missings anywhere in the observation. > > /* A related question: The following gives an incorrect answer. What in the > world is it doing? */ > egen junk=rowmean(*) list > Interesting one. I did a test, with the auto data: sysuse auto drop make egen junk = rowmean(_all) sum junk drop junk egen junk2 = rowmean(*) sum junk2 and also received different results. Setting -trace- on revealed that in the second case, Stata seems to be including a temporary variable (sort order?) into the calculation. It does look like a bug to me. HTH, Eva * * 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**:**Re: st: row mean (mean across columns)***From:*"Martin Weiss" <[email protected]>

**References**:**st: row mean (mean across columns)***From:*Jacob Wegelin <[email protected]>

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