Obtain First, Last, and Minimum

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To highlight some of the power of Essentia for batch processing operations, we have created a series of short demos. They use data from a fictional online casino. Data can be found in the casestudies/casino directory of the git repository. The data provides the username, time, bet (integer, US Dollars), winnings (float, US Dollars), and country of origin of their customers.

In this demo, we are interested in a summary table that provides the first time a user was seen in the system, the amount of the last bet they made, and the result of the ‘worst’ bet (lowest winnings, where negative indicates a loss).

In this script, we take the first time, last bet, and minimum winnings (worst loss) for each unique username in each unique country. We then order the results by the This demonstrates the ease with which Essentia can apply attributes to your data and return the results you want in the order you want them.

Primary Lines in this Script

Line 7

  • Store a table called grouping in the database worstloss that keeps track of the first value of the time column, last value of the bet column, and minimum value in the winnings column for each unique value of the country and user columns.

Line 11

  • Tell Essentia to look for data on your local datastore.

Line 13

  • Create a new rule to take any files in your home directory with ‘onlinecasino’ in their name and put them in the casino category. Also tell Essentia not to look for a date in the filenames.

Line 17

  • Pipe all files in the category casino to the aq_pp command.
  • In the aq_pp command, tell the preprocessor to take data from stdin, ignoring errors and skipping the first line (the header).
  • Then define the incoming data’s columns and import the data to the vector in the worstloss database so the attributes listed there can be applied.

Line 19

  • Internally sort the records in the database, within each unique country, by winnings. Since this is internal, it has no output.

Line 20

  • Export the modified and sorted data from the database and then save the results to a csv file.
 1     ess cluster set local
 3     ess udbd stop
 4     ess server reset
 6     ess drop database worstloss
 7     ess create database worstloss
 9     ess create table grouping s,pkey:country s,+key:user s,+first:time i,+last:bet f,+min:winnings
11     ess udbd start
13     ess select local
15     ess category add casino "$HOME/EssentiaPublic/*onlinecasino*" --dateregex none
17     ess summary
19     ess stream casino "*" "*" "aq_pp -f,+1,eok - -d s:user s:time i:bet f:winnings s:country -udb -imp worstloss:grouping" --debug
21     ess exec "aq_udb -ord worstloss:grouping winnings" --debug
22     ess exec "aq_udb -exp worstloss:grouping -o worstloss.csv" --debug