ride-cleansing/README.md

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# Lab: Filtering a Stream (Ride Cleansing)

If you haven't already done so, you'll need to first [setup your Flink development environment](../README.md). See [How to do the Labs](../README.md#how-to-do-the-labs) for an overall introduction to these exercises.

The task of the "Taxi Ride Cleansing" exercise is to cleanse a stream of TaxiRide events by removing events that do not start or end in New York City.

The `GeoUtils` utility class provides a static method `isInNYC(float lon, float lat)` to check if a location is within the NYC area.

### Input Data

This series of exercises is based a stream of `TaxiRide` events, as described in [Using the Taxi Data Streams](../README.md#using-the-taxi-data-streams).

### Expected Output

The result of the exercise should be a `DataStream<TaxiRide>` that only contains events of taxi rides which both start and end in the New York City area as defined by `GeoUtils.isInNYC()`.

The resulting stream should be printed to standard out.

## Getting Started

> :information_source: Rather than following the links to the sources in this section, you'll do better to find these classes in the flink-training project in your IDE.
> Both IntelliJ and Eclipse have ways to make it easy to search for and navigate to classes and files. For IntelliJ, see [the help on searching](https://www.jetbrains.com/help/idea/searching-everywhere.html), or simply press the Shift key twice and then continue typing something like `RideCleansing` and then select from the choices that popup.

### Exercise Classes

This exercise uses these classes:

- Java:  [`org.apache.flink.training.exercises.ridecleansing.RideCleansingExercise`](src/main/java/org/apache/flink/training/exercises/ridecleansing/RideCleansingExercise.java)
- Scala: [`org.apache.flink.training.exercises.ridecleansing.scala.RideCleansingExercise`](src/main/scala/org/apache/flink/training/exercises/ridecleansing/scala/RideCleansingExercise.scala)

### Tests

You will find the test for this exercise in

- Java:  [`org.apache.flink.training.exercises.ridecleansing.RideCleansingTest`](src/test/java/org/apache/flink/training/exercises/ridecleansing/RideCleansingTest.java)
- Scala: [`org.apache.flink.training.exercises.ridecleansing.scala.RideCleansingTest`](src/test/scala/org/apache/flink/training/exercises/ridecleansing/scala/RideCleansingTest.scala)

Like most of these exercises, at some point the `RideCleansingExercise` class throws an exception

```java
throw new MissingSolutionException();
```

Once you remove this line, the test will fail until you provide a working solution. You might want to first try something clearly broken, such as

```java
return false;
```

in order to verify that the test does indeed fail when you make a mistake, and then work on implementing a proper solution.

## Implementation Hints

<details>
<summary><strong>Filtering Events</strong></summary>

Flink's DataStream API features a `DataStream.filter(FilterFunction)` transformation to filter events from a data stream. The `GeoUtils.isInNYC()` function can be called within a `FilterFunction` to check if a location is in the New York City area. Your filter function should check both the starting and ending locations of each ride.
</details>

## Documentation

- [DataStream API](https://ci.apache.org/projects/flink/flink-docs-stable/dev/datastream_api.html)
- [Flink JavaDocs](https://ci.apache.org/projects/flink/flink-docs-stable/api/java/)

## Reference Solutions

Reference solutions are available in this project:

- Java:  [`org.apache.flink.training.solutions.ridecleansing.RideCleansingSolution`](src/solution/java/org/apache/flink/training/solutions/ridecleansing/RideCleansingSolution.java)
- Scala: [`org.apache.flink.training.solutions.ridecleansing.scala.RideCleansingSolution`](src/solution/scala/org/apache/flink/training/solutions/ridecleansing/scala/RideCleansingSolution.scala)

-----

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