st: shifting data inside panel data

[Tomáš Houška <xbender@gmail.com>]

Dear Statalist,

I have panel data of the following structure: "Store - Week -
Product_ID - Price - Quantity". Where there are multiple week data for
each store and multiple products being sold in each store every week.
Overall I have 36 stores, 28 products and 220 weeks, the data are in a
long format. The dataset is symmetric - all products were sold in
every store and in every week.

I am trying to create a new variable (lets call it "price_iv"), which
will be an instrumental variable for my demand analysis. I would like
the variable to contain for each product in each week prices from a
different store - i.e. I would like to shift the price data in the
"price" variable in such a way, that price of a product 1 in week one
and store 1 will correspond to the prices of product 1 in week in and
store 2 (or any other). Optimally each store will be used only once -
so at the end the data from all stores would be assigned to a
different store.
I havent been able to come up with a way, how to shift the data in an
appropriate way - Can you please help me solve this problem?

Thank you !
Tomas
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/