st: Unique values

["Natarajan Ramachandran" <NRamacha@maxwell.syr.edu>]

I have a couple of securities in a variable and their closing prices with a corresponding date.
 
(1) How do I loop through each security to find out the maximum closing price and the corresponding date?
 
(2) How do I loop through each security to find out the weekly returns?
 
Thanks for the responses.

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