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st: RE: generate new variable with frequencies


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: generate new variable with frequencies
Date   Tue, 4 Nov 2003 12:56:22 -0000

The frequencies of -type- can be put
in -typ_freq- by

bysort type : gen typ_freq = _N

If you want to scale to relative frequencies
(sum 1) then you can

su typ_freq, meanonly
replace typ_freq = typ_freq / r(sum)

and percents naturally can be obtained
with a factor of 100.

Some care will often be needed over
missing values:

bysort type : gen typ_freq = _N if !missing(type)
su typ_freq, meanonly
replace typ_freq = typ_freq / r(sum)

Another way to do it:

egen typ_freq = sum(1) if !missing(type), by(type)

Nick
n.j.cox@durham.ac.uk

Matteo Foschi
>
> We have a little trouble with a, we think, easy task.
> We want to generate a variable, which contains the relative
> frequency of
> another variable values.
> We have a variable, say “type”, and want to built a new variable,
> say “typ_freq”, which shows the relatively frequency of
> each value of “type”.
>
> We have tried first with the tablepc ado-file:
> tablepc type, generate (typ_freq)
> Therefore we obtain only the relatively frequency of each
> observation.
>
> We can obtain - in alternatively - the cumulated frequency
> (variable freqcum)
> with a little program:
>
> Generate freqcum =.
> ..
> sort typ_freq
> by typ_freq: gen groups = 1 if _n ==1
> replace groups = sum(groups)
> ..
> local K = groups[_N]
> local i 1
> while `i' <= `K' {
>  replace freqcum = sum(typ_freq)
>  local i = `i' + 1
> }
> ..
> We are not able, however,  to recode freq_cum or typ_freq
> in order to obtain
> the relatively frequency of each value of “type”, as bottom shows:
>
> Obs	Type  obs_freq  freq_cum   		typ_freq
> 1	1	1		1		2
> 2	1	1		2		2
> 3	2	1		3		3
> 4	2	1		4		3
> 5	2	1		5		3
> 6	3	1		6		1
> 7	4	1		7		2
> 8	4	1		8		2
> 9	5	1		9		1
> 10	6	1		10		1
>

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