# Re: st: Generating a list with combinations' counts and their description

 From n j cox To statalist@hsphsun2.harvard.edu Subject Re: st: Generating a list with combinations' counts and their description Date Wed, 23 May 2007 12:39:25 +0100

```Svend and Maarten are both right. Deep down, their answer
is the same, as -groups- is based on exactly the Stata
logic that Maarten exposes, plus bells and whistles.

Your original idea was good too.

egen group = group(var1 var2 var3), label
tab group

will do what you want as well. The -label- option
is crucial to get close to the display you want.
For examples more complicated, -groups- has more
handles.

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

Svend Juul
==========

Nick Cox made the -groups- command; it does what you want. Get it by:

ssc install groups

Maarten Buis
============

A rather blunt solution is shown below:

*-------------- begin example ------------
drop _all
input obs  var1 var2 var3
1      2     2     1
2      2     2     1
3      1     2     3
4      3     3     3
end

preserve
drop if missing(var1, var2, var3)
bys var1 var2 var3: gen N = _N
bys var1 var2 var3:  keep if _n == 1
list var1 var2 var3 N
restore
*---------- end example -----------------
(For more on how to use examples I sent to the Statalist, see
http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html )

V MA
====

I have 3 variables that can take the values 1 up to 3 and the data looks
something like this

obs var1 var2 var3
1 2 2 1
2 2 2 1
3 1 2 3
4 3 3 3

I would like to obtain a table that says how many observations I have of
each existing combination. But I would like this table to have a
"description" for each of the combinations. i.e. the resulting table
would be something like this:

var1 var2 var3 count
1 2 3 1
2 2 1 2
3 3 3 1

Note also that the lines in the table are ordered by the values of var1,
var2 and var3.

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```