st: xtile and "by" question

[Edgard Alfonso Polanco Aguilar <e-polanc@uniandes.edu.co>]

Hello everybody,

I'm working with a database which consists on income by month and 
region. I need to classify the income by percentiles by city and month 
because there's a wide dispersion on income levels across cities, to the 
point that the highest income in one is on the median of another. I know 
the command of choice for this task is xtile, but Stata doesn't allow me 
to use it with "by" like in "by city date: xtile var=income nq(10)". I'm 
working in Stata 9 SE for Windows.

Thaks!

Edgard

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