st: Cumulative Frequencies within Groups

["Ben Hoen" <bhoen@lbl.gov>]

Hi all,

I have been unable to figure out how to create cumulative frequencies within
groups.

This Nick Cox entry provided a great description for how to create
cumulative frequencies for a whole set of data:
http://www.stata.com/support/faqs/data-management/tabulating-cumulative-freq
uencies/ 

But I have not been able to apply the same logic to groups within my
dataset.

For the full dataset this code works perfectly (as Nick provided)

*======= Begin ===============

sysuse auto, clear
by rep78, sort: gen freq = _N
by rep78: gen cumfreq = _N if _n == 1
replace cumfreq = sum(cumfreq)
tabdisp rep78, cell(freq cumfreq)

* ========== End ==================

I would like to apply the same logic to groups of cases.  Here is my best
attempt.

* =========== Begin ===============

g levels=(int(4*runiform()))+1 //to create an categorical variable
representing 4 groups

su levels, meanonly

forvalues i = 1/`r(max)' { //max is used because often I will not know the
number of groups
 bys rep78: gen freqtemp=_N if levels==`i'
 by rep78: gen cumfreqtemp=_N if _n==1 & levels==`i'
 replace cumfreqtemp=sum(cumfreqtemp) if levels==`i'
 replace freq=freqtemp if levels==`i'
 replace cumfreq=cumfreqtemp if levels==`i'
 drop freqtemp cumfreqtemp

}
*

bys levels: tabdisp rep78, cell(freq cumfreq)

* =========== End =====================

As one can see, my code has a problem that I cannot discern.

Any ideas?

Thanks, in advance,

Ben


Ben Hoen
Principal Research Associate
Lawrence Berkeley National Laboratory
Office: 845-758-1896
Cell: 718-812-7589
bhoen@lbl.gov
http://eetd.lbl.gov/ea/emp/staff/hoen.html

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