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Re: st: How to keep if freq of var is >= 100 for both group (Alcohol "1" and non-alcohol "0")?
From
Nick Cox <[email protected]>
To
[email protected]
Subject
Re: st: How to keep if freq of var is >= 100 for both group (Alcohol "1" and non-alcohol "0")?
Date
Tue, 25 Sep 2012 08:31:14 +0100
This is a simple application of -by:-, with which all long-term Stata
users should be familiar.
bysort diagnosis group : keep if _N > 100
Note that this procedure just counts observations, and is indifferent
to missing values. If you have missing values on key variables, -drop-
them first.
Read the sections on -by:- in [U}. Then for a discursive tutorial on -by:-, see
SJ-2-1 pr0004 . . . . . . . . . . Speaking Stata: How to move step by: step
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. J. Cox
Q1/02 SJ 2(1):86--102 (no commands)
explains the use of the by varlist : construct to tackle
a variety of problems with group structure, ranging from
simple calculations for each of several groups to more
advanced manipulations that use the built-in _n and _N
Nick
On Tue, Sep 25, 2012 at 7:53 AM, Caliph Omar Moumin
<[email protected]> wrote:
>
> I have a large dataset which more than 500,000 observations; and more than 7000 diagnoses, which is grouped into two groups alcohol coded as "1" and nonlacloh as "0"
> the data structure is like this
>
> obs id diagnosis group............other variables
> 1 2338 A120 1
>
> 2 3838 m23 0
> .
> .
> .
> .
> 500,000 45566 y678 1
>
>
> So i want to keep if observations is >= 100 for both groups alcohol and nonalcohol based on daignoses. For example if daignoses A120 has more than 100 observations for both alcohol and nonalcohol keep if not drop it.
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