View source for Cholera MapReduce Application

[[File:John_Snow_memorial_and_pub.jpg|thumb]]

=Motivation=
[https://en.wikipedia.org/wiki/Epidemiology Epidemiology is the important study of "why certain people are getting ill."]

We get a chance to make sense of the data in a relatively open-ended studio.

=Background=

{{CollapsibleYouTube|Extra History: The Broad Street Pump|<youtube>TLpzHHbFrHY</youtube>

<youtube>1jlsyucUwpo</youtube>

<youtube>9NVT6iZP2qg</youtube>}}

Imagine you are [https://en.wikipedia.org/wiki/John_Snow a physician] in [https://en.wikipedia.org/wiki/1854_Broad_Street_cholera_outbreak 1854 London in the midst of a cholera outbreak].  Your theory that contaminated water is the cause meets resistance from the medical establishment which holds that it is spread via the air.

Imagine further that your friend [https://en.wikipedia.org/wiki/Ada_Lovelace Ada] has taught you to program.

=Lecture=
{{CollapsibleYouTube|CSE 231s Lecture: Cholera|<youtube>Ny5sjWGVuy0</youtube>}}

=Code To Use=
You will be asked to produce evidence from CholeraDeath locations and WaterPump locations.  The CholeraDeath data is from [https://www1.udel.edu/johnmack/frec682/cholera/cholera2.html this GIS Analysis] and made available in Java in [https://www.cse.wustl.edu/~dennis.cosgrove/courses/cse231/current/apidocs/mapreduce/apps/cholera/util/SohoCholeraOutbreak1854.html SohoCholeraOutbreak1854]. source: [https://web.archive.org/web/20160822002253/http://www1.udel.edu/johnmack/frec682/cholera/deaths.txt deaths.txt].

The WaterPump data is available via [https://www.cse.wustl.edu/~dennis.cosgrove/courses/cse231/current/apidocs/mapreduce/apps/cholera/core/WaterPump.html WaterPump.values()]<br/>source: [https://web.archive.org/web/20160822002256/http://www1.udel.edu/johnmack/frec682/cholera/pumps.txt pumps.txt].

[https://www.cse.wustl.edu/~cosgroved/courses/cse231/current/apidocs/mapreduce/apps/cholera/core/Location.html class Location]
: [https://www.cse.wustl.edu/~cosgroved/courses/cse231/current/apidocs/mapreduce/apps/cholera/core/Location.html#distanceTo-mapreduce.apps.cholera.core.Location- double distanceTo( Location other )]
: [https://www.cse.wustl.edu/~cosgroved/courses/cse231/current/apidocs/mapreduce/apps/cholera/core/Location.html#x double x()]
: [https://www.cse.wustl.edu/~cosgroved/courses/cse231/current/apidocs/mapreduce/apps/cholera/core/Location.html#y double y()]

[https://www.cse.wustl.edu/~cosgroved/courses/cse231/current/apidocs/mapreduce/apps/cholera/core/CholeraDeath.html class CholeraDeath]
: [https://www.cse.wustl.edu/~cosgroved/courses/cse231/current/apidocs/mapreduce/apps/cholera/core/CholeraDeath.html#location-- Location location()]

[https://www.cse.wustl.edu/~cosgroved/courses/cse231/current/apidocs/mapreduce/apps/cholera/core/WaterPump.html enum WaterPump]
: [https://www.cse.wustl.edu/~cosgroved/courses/cse231/current/apidocs/mapreduce/apps/cholera/core/WaterPump.html#location-- Location location()]

=Code To Implement=
In order to provide a more open-ended assignment, we have abstracted out different aspects of the studio. In particular, <code>getValueRepresentation()</code>  allows you to specify whether your CholeraApp sees high or low numbers as suspects. For example, if you return <code>ValueRepresentation.HIGH_NUMBERS_SUSPECT</code>, you are indicating that a higher number is more likely to indicate that the water pump is the source of the cholera outbreak.  This will aid the [[#Visualization]] in presenting your findings. 

We have anticipated two basic approaches to this problem (with a variation^2 on one of the approaches). You may choose to implement an integer-based or a double-based CholeraApp. If you take a different approach than one we have anticipated, that is fine.  Get it checked out by an instructor.

==CholeraOutbreak==

{{CodeToImplement|CholeraOutbreak|produceEvidence|mapreduce.apps.cholera.exercise}}

===valueRepresentation===
{{Sequential|public static ValueRepresentation valueRepresentation()}}

You have been provided with this implementation which should be sufficient:
<syntaxhighlight lang="java">
public static ValueRepresentation valueRepresentation() {
    return ValueRepresentation.AUTO_DETECT;
}
</syntaxhighlight>

===thresholdIfApplicable===
{{Sequential|public static Optional<Double> thresholdIfApplicable()}}

For the vast majority of students, a threshold value will not be applicable to their solution and thus this method need not to be changed:

<syntaxhighlight lang="java">
public static Optional<Double> thresholdIfApplicable() {
	final boolean IS_THRESHOLD_APPLICABLE = true;
	if (IS_THRESHOLD_APPLICABLE) {
		throw new NotYetImplementedException();
	} else {
		return Optional.empty();
	}
}
</syntaxhighlight>

However, if your solution has a threshold value which would be necessary for visualization and testing, return it here via Optional.of(threshold).

Again, you need not concern yourself with this method if you are going with a threshold-less strategy.


===produceEvidence(choleraDeaths)===
{{Sequential|public static Map<WaterPump, ? extends Number> produceEvidence(CholeraDeath[] choleraDeaths)}}

Note: [https://docs.oracle.com/javase/8/docs/api/java/lang/Integer.html Integer] and [https://docs.oracle.com/javase/8/docs/api/java/lang/Double.html Double] extend [https://docs.oracle.com/javase/8/docs/api/java/lang/Number.html Number].

How to leverage map reduce to solve this problem.

If going the Integer route:

<syntaxhighlight lang="java">
		Mapper<CholeraDeath, WaterPump, Integer> mapper = null; // TODO
		AccumulatorCombinerReducer<Integer, ?, Integer> accumulatorCombinerReducer = null; // TODO: note you have already created a class which will suffice here.
		MapReduceFramework<CholeraDeath, WaterPump, Integer, ?, Integer> framework = new StreamMapReduceFramework<>(mapper, accumulatorCombinerReducer);
		return framework.mapReduceAll(choleraDeaths);
</syntaxhighlight>

If going the Double route:

<syntaxhighlight lang="java">
		Mapper<CholeraDeath, WaterPump, Double> mapper = null; // TODO
		AccumulatorCombinerReducer<Double, ?, Double> accumulatorCombinerReducer = null; // TODO
		MapReduceFramework<CholeraDeath, WaterPump, Double, ?, Double> framework = new StreamMapReduceFramework<>(mapper, accumulatorCombinerReducer);
		return framework.mapReduceAll(choleraDeaths);
</syntaxhighlight>

{{Alert|You are allowed to and encouraged to create additional class file(s) and/or use code from previous exercises.}}

=Testing Your Solution=
==Visualization==
Original Map Drawn By John Snow:

[[File:Snow-cholera-map-1.jpg|400px]]

Our Visualization App:

{{Viz|CholeraOutbreakViz|mapreduce.apps.cholera.viz|main}}
[[File:CholeraOutbreak.png|600px]]

==Correctness==
If you have chosen to go a different route than the ones we anticipated, do not worry about passing the test suite.  Demo your work to an instructor in class and we can discuss its fitness.

{{TestSuite|_CholeraOutbreakTestSuite|mapreduce.apps.cholera.exercise}}

=Pledge, Acknowledgments, Citations=
{{Pledge|map-reduce-cholera-app}}