Collection of addons for Apache Pig
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pigaddons v0.1 (alpha) ====================== Contents: 1. About 2. Compiling 3. Contained Packages 4. Examples --------- 1. About --------- This is a repository containing UDFs and Addons for Apache Pig. It was created by Connor Woodson <http://www.connorwoodson.com> for the purpose of coding, and is released freely to the community under the MIT License (see LICENSE). The code contained herein is not perfect and might contain bugs (also known as hidden/incomplete features). If you have any comments, suggestions, or bug reports, please forward them to <firstname.lastname@example.org> for consideration. ------------- 2. Compiling ------------- This repository uses Maven as its dependency / build manager. To compile it, run mvn clean package from the command line, and the resulting JAR will be located in the targets/ directory. ---------------------- 3. Contained Packages ---------------------- _________________ A. RScriptEngine <http://theconnorcode.blogspot.com/2013/06/rpig-overview.html> ----------------- RScriptEngine is a scripting engine for Apache Pig that interprets the R language <http://www.r-project.org/>. The goal behind this scripting engine is compatability and ease use of the R language in Amazon EMR jobs. Included in /scripts is the rpig-bootstrap.sh script, that is meant as a bootstrap script for Amazon EMR instances; it can also be used on personal instances to set up an environment compatible with the scripting engine. This interpreter makes use of JRI <http://www.rforge.net/JRI/> to an instance of R to run inside of the Java process. It is a future goal to also support Rserve, which is another method of interacting with R from inside of Java. Required REGISTER statements: ----------------------------- REGISTER '/path/to/pigaddons-0.1-SNAPSHOT.jar'; REGISTER '/path/to/script.r' USING com.cwoodson.pigaddons.rpig.RScriptEngine AS namespace; Pre-Defined R Functions: ------------------------ Utils.installPackage(name) : wrapper to install and load the specified R package Utils.logInfo(info) : logs the given string as an info-level message Utils.logError(error) : logs the given string as an error-level message System Environment Variables: ----------------------------- (NOTE: these will do nothing until a future release) Define these by adding "-D<name>=<value>" to the Pig command call rpig.gfx.useJavaGD : when defined will set up the JavaGD package to connect with built-in functionality rpig.gfx.width : when using the above, specifies the graphics width rpig.gfx.height : when using the above, specifies the graphics height rpig.gfx.ps : when using the above, specifies the gfx point size ________________ B. FlumeStorage <> ---------------- In Progress ------------ 4. Examples ------------ ______________ A. NaiveBayes -------------- Naive Bayes is a classification-based machine learning algorithm. The provided example produces an implementation for classifying data where each field is a 1 or a 0 (yes/no, true/false, spam/not spam). By using a set of training data where the correct classification is known, a series of tables can be constructed (look at the R script for an explanation of the tables). These tables are then used for the data that gets tested. The probabilities that an event should be classified as 0 and as a 1 are both calculated, and the whichever classification produces the larger number is considered the correct classification. We implement a form of Naive Bayes known as LaPlace where we start with 1 in each cell of the tables; this helps solve issues where in the training data set a certain combination of correct classification / field value is never encountered. Having a 1 in this cell instead of a 0 prevents saying that the certain combination is impossible, but rather that we haven't seen that combination. To simplify the creation of the probabilities, we also take the Log of everything (so we are adding instead of multiplying); one result of this is that we don't end up with a number between 0 and 1 but rather a negative number such that e^number is the probability (I think). This example uses a randomly generated data set of 16 fields. For the training data, the first field is whether the event is classified as a 0 or 1, and the 16 fields follow that. Some notes about this example. The Pig script is dependent on the structure of the data / the number of fields, as we must declare a schema when we load the data sets that recognizes each field. We split the training data into two sets based off whether it is classified as 0 or 1 (not spam versus spam), and for both of these we sum up each field. This results in a count for spam/not spam for the number of times each field was a 0/1 in the training data (we also include the total number of records in each group). These numbers are turned in to the table used by Naive Bayes in the R script. The R script itself is self-contained and generalized to work on any input with the assumption of 0/1 as the only possible field values. The script starts with error checking on the input parameters to make sure that it is called correctly from Pig, and then it moves in to the algorithmic part. It returns a simple Tuple that contains the classification as well as the calculated log of the probabilities for each possible classification; the later two numbers are not really important, and so it could be made simpler by just returning a single value.