Hi,
   I have a huge text file of form
data is saved in directory data/data1.txt, data2.txt and so on
 merchant_id, user_id, amount
  1234, 9123, 299.2
  1233, 9199, 203.2
  1234, 0124, 230
  and so on..

What I want to do is for each merchant, find the average amount..
so basically in the end i want to save the output in file.
something like
merchant_id, average_amount
 1234, avg_amt_1234 a
  and so on.
How do I calculate the standard deviation as well?

Sorry for asking such a basic question. :(
Any help would be appreciated. :)
Jamal

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