Obtain First, Last, and Minimum

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 5

  • 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 9

  • Tell Essentia to look for data in your current directory.

Line 13

  • Create a new rule to take any files with ‘onlinecasino’ in their name and put them in the casino category.

Line 18

  • 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 20

  • 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.
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ess instance local
ess spec drop database worstloss
ess spec create database worstloss --ports=1

ess spec create table grouping s,pkey:country s,+key:user s,+first:time i,+last:bet f,+min:winnings

ess udbd start

ess datastore select .

ess datastore scan

ess datastore rule add "*onlinecasino*" "casino"

ess datastore probe casino --apply
ess datastore summary

ess task stream casino "*" "*" "aq_pp -f,+1,eok - -d s:user s:time i:bet f:winnings s:country -udb_imp worstloss:grouping" --debug

ess task exec "aq_udb -db worstloss -ord grouping winnings" --debug
ess task exec "aq_udb -db worstloss -exp grouping -o worstloss.csv" --debug

ess udbd stop