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st: by and missing values question

From   Nikolaos Kanellopoulos <>
Subject   st: by and missing values question
Date   Mon, 11 May 2009 08:22:41 +0000 (GMT)

I have written the following very simple program

cap pr drop logdiff
program define logdiff , rclass byable(recall)

    syntax varlist(min=2 max=2) [if] [in] [fweight aweight] 

    version 8.0
    tempvar dif
    marksample touse 
    qui count 
    local N = r(N)

    qui count if `touse'
    if r(N) == 0 error 2000
    local n = r(N)

    qui gen `dif' = (`n'/`N')*abs(ln(`2') - ln(`1'))  if `touse'    
    qui su  `dif' if `touse' [`weight'`exp'] , meanonly
    loc diff = r(mean)
    di as text "Log Difference: " as result `diff'
    return scalar diff = `diff'
    return local N = `N'
    return local n = `n'

My questions are:

[1] How can I return the results for all categories when I use the by option and not only for the last category?

[2] How can I display and return the results for the total of a category when I use the by option? i.e. return the same results as without the by option.

[3] How can I exclude the missing values from my estimations both when I use and not use the by option?

Thanks in advance

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