The point is that in ur application u treat (1,2) and (2,1) as different, but sometimes 'uniq' shall mean a 'communication' between the 2 'factors' and then the different treatment is wrong. At first I was up to think that the short formula would not differentiate between them opposed to my (very long) solution to ur problem. But the not differentiating solution is the problematic one.

21.11.2013 16:25, Giuseppe Vittucci:
I don't see your point...
In your case ndigits is 0 and therefore: 

unique = region * 10 + sector 

This is enough to produce unique values for each region/sector
combination.
(1,2) and (2,1) must be treated as different and they do...


On Thu, 2013-11-21 at 15:57 +0100, Pindar wrote:

Yes, nice, but one has to check that 'region' and 'sector' do not
share a common cluster ID like in

<hansl> 
region = randgen(i,1,10) 
sector = randgen(i,1,5) 
<hansl> 

Since combinations like (1,2) and (2,1) are treated as being
different.
Hence, with a primary data manipulation 'sector = randgen(i,1,5) +100'
things should be fine.

21.11.2013 15:13, Riccardo (Jack) Lucchetti:


On Thu, 21 Nov 2013, Giuseppe Vittucci wrote: 


Hi, 

I have firm level data and two categorical variables (region and 
sector). 
I need to define another variable which is an index identifying
the 
unique combinations region-sector each firm belongs to, so I can
use it 
in computing cluster-robust s.e. 

One way to do this is to use the command "values" for region and
sector 
and then use a nested loop, but this seems quite
time-consuming... 

Is there a simpler way in gretl to do it? 

You mean, like this? 

<hansl> 
nulldata 1024 

# simulated data 
region = randgen(i,1,20) 
sector = randgen(i,10,99) 
# ---------------------------------------------- 
scalar ndigits = floor(log10(max(sector))) 
series unique = region * 10^(ndigits+1) + sector 
</hansl> 


------------------------------------------------------- 
  Riccardo (Jack) Lucchetti 
  Dipartimento di Scienze Economiche e Sociali (DiSES) 

  Università Politecnica delle Marche 
  (formerly known as Università di Ancona) 

  r.lucchetti@univpm.it 
  http://www2.econ.univpm.it/servizi/hpp/lucchetti 
-------------------------------------------------------


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