Introduction

Apache Spark is an open-source, distributed, general-purpose analytics engine. For years, it has been a staple in the Big Data ecosystem for batch and real-time processing on large datasets. Although native support for the platform is limited to the JVM set of languages, other languages typically used for data processing and analytics like Python and R have plugged into Spark’s Interop layer to make use of its functionality. Around the Build 2019 conference, Microsoft announced Spark.NET. Spark.NET provides bindings written for the Spark Interop layer that allow you to work with components like Spark SQL and Spark Streaming inside your .NET applications. Because Spark.NET is .NET Standard 2.0 compliant, it can run operating systems like Windows, Mac and Linux. Spark.NET is an evolution of the Mobius project which provided .NET bindings for Spark.

This sample takes a restaurant violation dataset from the NYC Open Data portal and processes it using Spark.NET. Then, the processed data is used to train a machine learning model that attempts to predict the grade an establishment will receive after an inspection. The model will be trained using ML.NET, an open-source, cross-platform machine learning framework. Finally, data for which no grade currently exists will be enriched using the trained model to assign an expected grade.

The source code for this sample can be found in the lqdev/RestaurantInspectionsSparkMLNET

GitHub repo.

This project was built using Ubuntu 18.04 but should work on Windows and Mac devices.

Install Java

Since Spark runs on the JVM, you’ll need Java on your PC. The minimum version required is version 8. To install and Java, enter the following command into the terminal:

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sudo apt install openjdk-8-jdk openjdk-8-jre



Then, make sure that the recently installed version is the default

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sudo update-alternatives --config java



Download and configure Spark

Download Spark 2.4.1 with Hadoop 2.7 onto your computer. In this case, I’m placing it into my Downloads folder.

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wget https://archive.apache.org/dist/spark/spark-2.4.1/spark-2.4.1-bin-hadoop2.7.tgz -O ~/Downloads/spark-2.4.1-bin-hadoop2.7.tgz



Extract the contents of the recently downloaded file into the /usr/bin/local directory.

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sudo tar -xvf ~/Downloads/spark-2.4.1-bin-hadoop2.7.tgz --directory /usr/ local /bin



Download and configure .NET Spark Worker

Download the .NET Spark worker onto your computer. In this case, I’m placing it into the Downloads folder.

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wget https://github.com/dotnet/spark/releases/download/v0.4.0/Microsoft.Spark.Worker.netcoreapp2.1.linux-x64-0.4.0.tar.gz -O ~/Downloads/Microsoft.Spark.Worker.netcoreapp2.1.linux-x64-0.4.0.tar.gz



Extract the contents of the recently downloaded file into the /usr/bin/local directory.

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sudo tar -xvf ~/Downloads/Microsoft.Spark.Worker.netcoreapp2.1.linux-x64-0.4.0.tar.gz --directory /usr/ local /bin



Finally, raise the permissions on the Microsoft.Spark.Worker program. This is required to execute User-Defined Functions (UDF).

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sudo chmod +x /usr/ local /bin/Microsoft.Spark.Worker-0.4.0/Microsoft.Spark.Worker



Configure environment variables

Once you download and configure the pre-requisites, configure their locations in the system as environment variables. Open the ~/.bashrc file and add the following content at the end of the file.

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export SPARK_PATH=/usr/ local /bin/spark-2.4.1-bin-hadoop2.7

export PATH= $SPARK_PATH /bin: $PATH

export HADOOP_HOME= $SPARK_PATH

export SPARK_HOME= $SPARK_PATH

export DOTNET_WORKER_DIR=/usr/ local /bin/Microsoft.Spark.Worker-0.4.0



Solution description

Understand the data

The dataset used in this solution is the DOHMH New York City Restaurant Inspection Results and comes from the NYC Open Data portal. It is updated daily and contains assigned and pending inspection results and violation citations for restaurants and college cafeterias. The dataset excludes establishments that have gone out of business. Although the dataset contains several columns, only a subset of them are used in this solution. For a detailed description of the dataset, visit the dataset website.

Understand the solution

This solution is made up of four different .NET Core applications:

RestaurantInspectionsETL: .NET Core Console application that takes raw data and uses Spark.NET to clean and transform the data into a format that is easier to use as input for training and making predictions with a machine learning model built with ML.NET.

RestaurantInspectionsML: .NET Core Class Library that defines the input and output schema of the ML.NET machine learning model. Additionally, this is where the trained model is saved to.

RestaurantInspectionsTraining: .NET Core Console application that uses the graded data generated by the RestaurantInspectionsETL application to train a multiclass classification machine learning model using ML.NET’s Auto ML.

RestaurantInspectionsEnrichment: .NET Core Console application that uses the ungraded data generated by the RestaurantInspectionsETL application as input for the trained ML.NET machine learning model which predicts what grade an establishment is most likely to receive based on the violations found during inspection.

Set up the solution

Create solution directory

Create a new directory for your projects called RestaurantInspectionsSparkMLNET and navigate to it with the following command.

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mkdir RestaurantInspectionsSparkMLNET && cd RestaurantInspectionsSparkMLNET



Then, create a solution using the dotnet cli .

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dotnet new sln



To ensure that the 2.1 version of the .NET Core SDK is used as the target framework, especially if you have multiple versions of the .NET SDK installed, create a file called globals.json in the RestaurantInspectionsSparkMLNET solution directory.

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touch global.json



In the global.json file, add the following content. Make sure to use the specific version of the SDK installed on your computer. In this case, I have version 2.1.801 installed on my computer. You can use the dotnet --list-sdks command to list the installed SDK versions.

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{

"sdk" : {

"version" : "2.1.801"

}

}



Create and configure the ETL project

The ETL project is responsible for taking the raw source data and using Spark to apply a series of transformations to prepare the data to train the machine learning model as well as to enrich data with missing grades.

Inside the RestaurantInspectionsSparkMLNET solution directory, create a new console application called RestaurantInspectionsETL using the dotnet cli .

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dotnet new console -o RestaurantInspectionsETL



Add the newly created project to the solution with the dotnet cli .

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dotnet sln add ./RestaurantInspectionsETL/



Since this project uses the Microsoft.Spark NuGet package, use the dotnet cli to install it.

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dotnet add ./RestaurantInspectionsETL/ package Microsoft.Spark --version 0.4.0



Create and configure the ML model project

The ML model class library will contain the domain model that defines the schema of model inputs and outputs as well as the trained model itself.

Inside the RestaurantInspectionsSparkMLNET solution directory, create a new class library called RestaurantInspectionsML using the dotnet cli .

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dotnet new classlib -o RestaurantInspectionsML



Add the newly created project to the solution with the dotnet cli .

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dotnet sln add ./RestaurantInspectionsML/



Since this project uses the Microsoft.ML NuGet package, use the dotnet cli to install it.

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dotnet add ./RestaurantInspectionsML/ package Microsoft.ML --version 1.3.1



Create and configure the ML training project

The purpose of the training project is to use the pre-processed graded data output by the RestaurantInspectionsETL project as input to train a multiclass classification model with ML.NET’s Auto ML API. The trained model will then be saved in the RestaurantInspectionsML directory.

Inside the RestaurantInspectionsSparkMLNET solution directory, create a new console application called RestaurantInspectionsTraining using the dotnet cli .

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dotnet new console -o RestaurantInspectionsTraining



Add the newly created project to the solution with the dotnet cli .

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dotnet sln add ./RestaurantInspectionsTraining/



This project depends on the domain model created in the RestaurantInspectionsML project, so you need to add a reference to it.

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dotnet add ./RestaurantInspectionsTraining/ reference ./RestaurantInspectionsML/



Since this project uses the Microsoft.Auto.ML NuGet package, use the dotnet cli to install it.

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dotnet add ./RestaurantInspectionsTraining/ package Microsoft.ML.AutoML --version 0.15.1



Create and configure the data enrichment project

The data enrichment application uses the trained machine learning model created by the RestaurantInspectionsTraining application and use it on the pre-processed ungraded data created by the RestaurantInspectionsETL application to predict what grade that establishment is most likely to receive based on the violations found during inspection.

Inside the RestaurantInspectionsSparkMLNET solution directory, create a new console application called RestaurantInspectionsEnrichment using the dotnet cli .

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dotnet new console -o RestaurantInspectionsEnrichment



Add the newly created project to the solution with the dotnet cli .

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dotnet sln add ./RestaurantInspectionsEnrichment/



This project depends on the domain model created in the RestaurantInspectionsML project, so you need to add a reference to it.

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dotnet add ./RestaurantInspectionsEnrichment/ reference ./RestaurantInspectionsML/



This uses the following NuGet packages:

Microsoft.Spark

Microsoft.ML.LightGBM (This is not required but predictions may fail if the final model is a LightGBM model).

Install the packages with the following commands:

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dotnet add ./RestaurantInspectionsEnrichment/ package Microsoft.Spark --version 0.4.0

dotnet add ./RestaurantInspectionsEnrichment/ package Microsoft.ML.LightGBM --version 1.3.1



Build ETL application

The first step is to prepare the data. To do so, apply a set of transformations using Spark.NET.

Download the data

Navigate to the RestaurantInspectionsETL project and create a Data directory.

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mkdir Data



Then, download the data into the newly created Data directory.

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wget https://data.cityofnewyork.us/api/views/43nn-pn8j/rows.csv?accessType=DOWNLOAD -O Data/NYC-Restaurant-Inspections.csv



Build the ETL pipeline

Add the following usings to the Program.cs file.

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using System;

using System.IO;

using Microsoft.Spark.Sql;

using static Microsoft.Spark.Sql.Functions;



Not all of the columns are relevant. Inside the Main method of the Program.cs file, define the columns to be removed.

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string [] dropCols = new string []

{

"CAMIS" ,

"CUISINE DESCRIPTION" ,

"VIOLATION DESCRIPTION" ,

"BORO" ,

"BUILDING" ,

"STREET" ,

"ZIPCODE" ,

"PHONE" ,

"ACTION" ,

"GRADE DATE" ,

"RECORD DATE" ,

"Latitude" ,

"Longitude" ,

"Community Board" ,

"Council District" ,

"Census Tract" ,

"BIN" ,

"BBL" ,

"NTA"

};



The entrypoint of Spark applications is the SparkSession . Create SparkSession inside the Main method of the Program.cs file.

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var sc =

SparkSession

.Builder()

.AppName( "Restaurant_Inspections_ETL" )

.GetOrCreate();



Then, load the data stored in the NYC-Restaurant-Inspections.csv file into a DataFrame .

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DataFrame df =

sc

.Read()

.Option( "header" , "true" )

.Option( "inferSchema" , "true" )

.Csv( "Data/NYC-Restaurant-Inspections.csv" );



DataFrames can be thought of as tables in a database or sheets in Excel. Spark has various ways of representing data but DataFrames are the format supported by Spark.NET. Additionally, the DataFrame API is higher-level and easier to work with.

Once the data is loaded, get rid of the data that are not needed by creating a new DataFrame that excludes the dropCols as well as missing values.

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DataFrame cleanDf =

df

.Drop(dropCols)

.WithColumnRenamed( "INSPECTION DATE" , "INSPECTIONDATE" )

.WithColumnRenamed( "INSPECTION TYPE" , "INSPECTIONTYPE" )

.WithColumnRenamed( "CRITICAL FLAG" , "CRITICALFLAG" )

.WithColumnRenamed( "VIOLATION CODE" , "VIOLATIONCODE" )

.Na()

.Drop();



Typically, machine learning models expect values to be numerical, so in the ETL step try to convert as many values as possible into numerical values. The CRITICALFLAG column contains “Y”/“N” values that can be encoded as 0 and 1.

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DataFrame labeledFlagDf =

cleanDf

.WithColumn( "CRITICALFLAG" ,

When(Functions.Col( "CRITICALFLAG" ) == "Y" , 1 )

.Otherwise( 0 ));



This dataset contains one violation per row which correspond to different inspections. Therefore, all of the violations need to be aggregated by business and inspection.

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DataFrame groupedDf =

labeledFlagDf

.GroupBy( "DBA" , "INSPECTIONDATE" , "INSPECTIONTYPE" , "CRITICALFLAG" , "SCORE" , "GRADE" )

.Agg(Functions.CollectSet(Functions.Col( "VIOLATIONCODE" )).Alias( "CODES" ))

.Drop( "DBA" , "INSPECTIONDATE" )

.WithColumn( "CODES" , Functions.ArrayJoin(Functions.Col( "CODES" ), "," ))

.Select( "INSPECTIONTYPE" , "CODES" , "CRITICALFLAG" , "SCORE" , "GRADE" );



Now that the data is in the format used to train and make predictions, split the cleaned DataFrame into two new DataFrames , graded and ungraded. The graded dataset is the data used for training the machine learning model. The ungraded data will be used for enrichment.

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DataFrame gradedDf =

groupedDf

.Filter(

Col( "GRADE" ) == "A" |

Col( "GRADE" ) == "B" |

Col( "GRADE" ) == "C" );



DataFrame ungradedDf =

groupedDf

.Filter(

Col( "GRADE" ) != "A" &

Col( "GRADE" ) != "B" &

Col( "GRADE" ) != "C" );



Take the DataFrames and save them as csv files for later use.

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var timestamp = ((DateTimeOffset) DateTime.UtcNow).ToUnixTimeSeconds().ToString();



var saveDirectory = Path.Join( "Output" ,timestamp);



if (!Directory.Exists(saveDirectory))

{

Directory.CreateDirectory(saveDirectory);

}



gradedDf.Write().Csv(Path.Join(saveDirectory, "Graded" ));



ungradedDf.Write().Csv(Path.Join(saveDirectory, "Ungraded" ));



Publish and run the ETL application

The final Program.cs file should look as follows:

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using System;

using System.IO;

using Microsoft.Spark.Sql;

using static Microsoft.Spark.Sql.Functions;



namespace RestaurantInspectionsETL

{

class Program

{

static void Main ( string [] args )

{



string [] dropCols = new string []

{

"CAMIS" ,

"CUISINE DESCRIPTION" ,

"VIOLATION DESCRIPTION" ,

"BORO" ,

"BUILDING" ,

"STREET" ,

"ZIPCODE" ,

"PHONE" ,

"ACTION" ,

"GRADE DATE" ,

"RECORD DATE" ,

"Latitude" ,

"Longitude" ,

"Community Board" ,

"Council District" ,

"Census Tract" ,

"BIN" ,

"BBL" ,

"NTA"

};





var sc =

SparkSession

.Builder()

.AppName( "Restaurant_Inspections_ETL" )

.GetOrCreate();





DataFrame df =

sc

.Read()

.Option( "header" , "true" )

.Option( "inferSchema" , "true" )

.Csv( "Data/NYC-Restaurant-Inspections.csv" );





DataFrame cleanDf =

df

.Drop(dropCols)

.WithColumnRenamed( "INSPECTION DATE" , "INSPECTIONDATE" )

.WithColumnRenamed( "INSPECTION TYPE" , "INSPECTIONTYPE" )

.WithColumnRenamed( "CRITICAL FLAG" , "CRITICALFLAG" )

.WithColumnRenamed( "VIOLATION CODE" , "VIOLATIONCODE" )

.Na()

.Drop();





DataFrame labeledFlagDf =

cleanDf

.WithColumn( "CRITICALFLAG" ,

When(Functions.Col( "CRITICALFLAG" ) == "Y" , 1 )

.Otherwise( 0 ));





DataFrame groupedDf =

labeledFlagDf

.GroupBy( "DBA" , "INSPECTIONDATE" , "INSPECTIONTYPE" , "CRITICALFLAG" , "SCORE" , "GRADE" )

.Agg(Functions.CollectSet(Functions.Col( "VIOLATIONCODE" )).Alias( "CODES" ))

.Drop( "DBA" , "INSPECTIONDATE" )

.WithColumn( "CODES" , Functions.ArrayJoin(Functions.Col( "CODES" ), "," ))

.Select( "INSPECTIONTYPE" , "CODES" , "CRITICALFLAG" , "SCORE" , "GRADE" );





DataFrame gradedDf =

groupedDf

.Filter(

Col( "GRADE" ) == "A" |

Col( "GRADE" ) == "B" |

Col( "GRADE" ) == "C" );



DataFrame ungradedDf =

groupedDf

.Filter(

Col( "GRADE" ) != "A" &

Col( "GRADE" ) != "B" &

Col( "GRADE" ) != "C" );





var timestamp = ((DateTimeOffset) DateTime.UtcNow).ToUnixTimeSeconds().ToString();



var saveDirectory = Path.Join( "Output" ,timestamp);



if (!Directory.Exists(saveDirectory))

{

Directory.CreateDirectory(saveDirectory);

}



gradedDf.Write().Csv(Path.Join(saveDirectory, "Graded" ));



ungradedDf.Write().Csv(Path.Join(saveDirectory, "Ungraded" ));

}

}

}



Publish the application with the following command.

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dotnet publish -f netcoreapp2.1 -r ubuntu.18.04-x64



Run the application with spark-submit .

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spark-submit --class org.apache.spark.deploy.dotnet.DotnetRunner --master local bin/Debug/netcoreapp2.1/ubuntu.18.04-x64/publish/microsoft-spark-2.4.x-0.4.0.jar dotnet bin/Debug/netcoreapp2.1/ubuntu.18.04-x64/publish/RestaurantInspectionsETL.dll



Build ML Domain

Define the model input schema

Navigate to the RestaurantInspectionsTraining project directory and create a new file called ModelInput.cs.

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touch ModelInput.cs



Open the ModelInput.cs file and add the following code.

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using Microsoft.ML.Data;



namespace RestaurantInspectionsML

{

public class ModelInput

{

[ ]

public string InspectionType { get ; set ; }



[ ]

public string Codes { get ; set ; }



[ ]

public float CriticalFlag { get ; set ; }



[ ]

public float InspectionScore { get ; set ; }



[ ]

[ ]

public string Grade { get ; set ; }

}

}



Using attributes in the schema, five properties are defined:

InspectionType: The type of inspection performed.

Codes: Violation codes found during inspection.

CriticalFlag: Indicates if any of the violations during the inspection were critical (contribute to food-borne illness).

InspectionScore: Score assigned after inspection.

Grade: Letter grade assigned after inspection

The LoadColumn attribute defines the position of the column in the file. Data in the last column is assigned to the Grade property but is then referenced as Label in the IDataView . The reason for using the ColumnName attribute is ML.NET algorithms have default column names and renaming properties at the schema class level removes the need to define the feature and label columns as parameters in the training pipeline.

Define the model output schema

In the RestaurantInspectionsTraining project directory and create a new file called ModelOutput.cs.

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touch ModelOutput.cs



Open the ModelOutput.cs file and add the following code.

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namespace RestaurantInspectionsML

{

public class ModelOutput

{

public float [] Scores { get ; set ; }

public string PredictedLabel { get ; set ; }

}

}



For the output schema, the ModelOutput class uses properties with the default column names of the outputs generated by the model training process:

Scores: A float vector containing the probabilties for all the predicted classes.

PredictedLabel: The value of the prediction. In this case, the PredictedLabel is the predicted grade expected to be assigned after inspection given the set of features for that inspection.

Build the model training application

The application trains a multiclass classification algorithm. Finding the “best” algorithm with the right parameters requires experimentation. Fortunately, ML.NET’s Auto ML does this for you given you provide it with the type of algorithm you want to train.

Load the graded data

Navigate to the RestaurantInspectionsTraining project directory and add the following using statements to the Program.cs class.

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using System;

using System.IO;

using System.Linq;

using Microsoft.ML;

using static Microsoft.ML.DataOperationsCatalog;

using Microsoft.ML.AutoML;

using RestaurantInspectionsML;



Inside the Main method of the Program.cs file, define the path where the data files are stored.

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string solutionDirectory = "/home/lqdev/Development/RestaurantInspectionsSparkMLNET" ;

string dataLocation = Path.Combine(solutionDirectory, "RestaurantInspectionsETL" , "Output" );



The entrypoint of an ML.NET application is the MLContext . Initialize an MLContext instance.

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MLContext mlContext = new MLContext();



Next, get the paths of the data files. The output generated by the RestaurantInspectionsETL application contains both the csv files as well as files containing information about the partitions that created them. For training, only the csv files are needed.

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var latestOutput =

Directory

.GetDirectories(dataLocation)

.Select(directory => new DirectoryInfo(directory))

.OrderBy(directoryInfo => directoryInfo.Name)

.Select(directory => Path.Join(directory.FullName, "Graded" ))

.First();



var dataFilePaths =

Directory

.GetFiles(latestOutput)

.Where(file => file.EndsWith( "csv" ))

.ToArray();



Then, load the data into an IDataView . An IDataView is similar to a DataFrame in that it is a way to represent data as rows, columns and their schema.

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var dataLoader = mlContext.Data.CreateTextLoader<ModelInput>(separatorChar: ',' , hasHeader: false , allowQuoting: true , trimWhitespace: true );



IDataView data = dataLoader.Load(dataFilePaths);



It’s good practice to split the data into training and test sets for evaluation. Split the data into 80% training and 20% test sets.

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TrainTestData dataSplit = mlContext.Data.TrainTestSplit(data,testFraction: 0.2 );

IDataView trainData = dataSplit.TrainSet;

IDataView testData = dataSplit.TestSet;



Create the experiment

Auto ML takes the data and runs experiments using different models and hyper-parameters in search of the “best” model. Define the settings for your experiment. In this case, the model will run for 600 seconds or 10 minutes and will try to find the model with the lowest log loss metric.

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var experimentSettings = new MulticlassExperimentSettings();

experimentSettings.MaxExperimentTimeInSeconds = 600 ;

experimentSettings.OptimizingMetric = MulticlassClassificationMetric.LogLoss;



Then, create the experiment.

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var experiment = mlContext.Auto().CreateMulticlassClassificationExperiment(experimentSettings);



After creating the experiment, run it.

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var experimentResults = experiment.Execute(data, progressHandler: new ProgressHandler());



By default, running the application won’t display progress information. However, a ProgressHandler object can be passed into the Execute method of an experiment which calls the implemented Report method.

Inside the RestaurantInspectionsTraining project directory, create a new file called ProgressHandler.cs.

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touch ProgressHandler.cs



Then, add the following code:

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using System;

using Microsoft.ML.Data;

using Microsoft.ML.AutoML;



namespace RestaurantInspectionsTraining

{

public class ProgressHandler : IProgress<RunDetail<MulticlassClassificationMetrics>>

{

public void Report ( RunDetail<MulticlassClassificationMetrics> run )

{

Console.WriteLine( $"Trained {run.TrainerName} with Log Loss {run.ValidationMetrics.LogLoss: 0. ####} in {run.RuntimeInSeconds: 0. ##} seconds" );

}

}

}



The ProgressHandler class derives from the IProgress<T> interface which requires the implementation of the Report method. The object being passed into the Report method after each run is an RunDetail<MulticlassClassificationMetrics> object. Each time a run is complete, the Report method is called and the code inside it executes.

Evaluate the results

Once the experiment has finished running, get the model from the best run. Add the following code to the Main method of the Program.cs.

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var bestModel = experimentResults.BestRun.Model;



Evaluate the performance of the model using the test dataset and measure it’s Micro-Accuracy metric.

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IDataView scoredTestData = bestModel.Transform(testData);

var metrics = mlContext.MulticlassClassification.Evaluate(scoredTestData);

Console.WriteLine( $"MicroAccuracy: {metrics.MicroAccuracy} " );



Save the trained model

Finally, save the trained model to the RestaurantInspectionsML project.

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string modelSavePath = Path.Join(solutionDirectory, "RestaurantInspectionsML" , "model.zip" );

mlContext.Model.Save(bestModel, data.Schema, modelSavePath);



A file called model.zip should be created inside the RestaurantInspectionsML project.

Make sure that the trained model file is copied to the output directory by adding the following contents to the RestaurantInspectionsML.csproj file in the RestaurantInspectionsML directory.

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< ItemGroup >

< None Include = "model.zip" >

< CopyToOutputDirectory > PreserveNewest </ CopyToOutputDirectory >

</ None >

</ ItemGroup >



Copying it to the output directory of the RestaurantInspectionsML makes it easier to reference from the RestaurantInspectionsEnrichment project since that project already contains a reference to the RestaurantInspectionsML class library.

Train the model

The final Program.cs file should look as follows:

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using System;

using System.IO;

using System.Linq;

using Microsoft.ML;

using static Microsoft.ML.DataOperationsCatalog;

using Microsoft.ML.AutoML;

using RestaurantInspectionsML;



namespace RestaurantInspectionsTraining

{

class Program

{

static void Main ( string [] args )

{



string solutionDirectory = "/home/lqdev/Development/RestaurantInspectionsSparkMLNET" ;

string dataLocation = Path.Combine(solutionDirectory, "RestaurantInspectionsETL" , "Output" );





MLContext mlContext = new MLContext();





var latestOutput =

Directory

.GetDirectories(dataLocation)

.Select(directory => new DirectoryInfo(directory))

.OrderBy(directoryInfo => directoryInfo.Name)

.Select(directory => Path.Join(directory.FullName, "Graded" ))

.First();



var dataFilePaths =

Directory

.GetFiles(latestOutput)

.Where(file => file.EndsWith( "csv" ))

.ToArray();





var dataLoader = mlContext.Data.CreateTextLoader<ModelInput>(separatorChar: ',' , hasHeader: false , allowQuoting: true , trimWhitespace: true );

IDataView data = dataLoader.Load(dataFilePaths);





TrainTestData dataSplit = mlContext.Data.TrainTestSplit(data,testFraction: 0.2 );

IDataView trainData = dataSplit.TrainSet;

IDataView testData = dataSplit.TestSet;





var experimentSettings = new MulticlassExperimentSettings();

experimentSettings.MaxExperimentTimeInSeconds = 600 ;

experimentSettings.OptimizingMetric = MulticlassClassificationMetric.LogLoss;





var experiment = mlContext.Auto().CreateMulticlassClassificationExperiment(experimentSettings);





var experimentResults = experiment.Execute(data, progressHandler: new ProgressHandler());





var bestModel = experimentResults.BestRun.Model;





IDataView scoredTestData = bestModel.Transform(testData);

var metrics = mlContext.MulticlassClassification.Evaluate(scoredTestData);

Console.WriteLine( $"MicroAccuracy: {metrics.MicroAccuracy} " );





string modelSavePath = Path.Join(solutionDirectory, "RestaurantInspectionsML" , "model.zip" );

mlContext.Model.Save(bestModel, data.Schema, modelSavePath);

}

}

}



Once all the code and configurations are complete, from the RestaurantInspectionsTraining directory, run the application using the dotnet cli . Remember this will take 10 minutes to run.

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dotnet run



The console output should look similar to the output below:

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Trained LightGbmMulti with Log Loss 0.1547 in 1.55 seconds

Trained FastTreeOva with Log Loss 0.0405 in 65.58 seconds

Trained FastForestOva with Log Loss 0.0012 in 53.37 seconds

Trained LightGbmMulti with Log Loss 0.0021 in 4.55 seconds

Trained FastTreeOva with Log Loss 0.8315 in 5.22 seconds

MicroAccuracy: 0.999389615839469



Build the data enrichment application

Now that the model is trained, it can be used to enrich the ungraded data.

Initialize the PredictionEngine

Navigate to the RestaurantInspectionsEnrichment project directory and add the following using statements to the Program.cs class.

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using System.IO;

using System.Linq;

using Microsoft.ML;

using Microsoft.Spark.Sql;

using static Microsoft.Spark.Sql.Functions;

using RestaurantInspectionsML;



To make predictions, the model has to be loaded into the applicaton and because predictions are made one row at a time, a PredictionEngine has be created as well.

Inside the Program class, define the PredictionEngine .

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private static readonly PredictionEngine<ModelInput,ModelOutput> _predictionEngine;



Then, create a constructor to load the model and initialize it.

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static Program ( )

{

MLContext mlContext = new MLContext();

ITransformer model = mlContext.Model.Load( "model.zip" , out DataViewSchema schema);

_predictionEngine = mlContext.Model.CreatePredictionEngine<ModelInput,ModelOutput>(model);

}



Load the ungraded data

In the Main method of the Program class, define the location of the data files.

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string solutionDirectory = "/home/lqdev/Development/RestaurantInspectionsSparkMLNET" ;

string dataLocation = Path.Combine(solutionDirectory, "RestaurantInspectionsETL" , "Output" );



Then, get the path of the most recent ungraded data generated by the RestaurantInspectionsETL application.

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var latestOutput =

Directory

.GetDirectories(dataLocation)

.Select(directory => new DirectoryInfo(directory))

.OrderBy(directoryInfo => directoryInfo.Name)

.Select(directory => directory.FullName)

.First();



Initialize a SparkSession for your enrichment application.

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var sc =

SparkSession

.Builder()

.AppName( "Restaurant_Inspections_Enrichment" )

.GetOrCreate();



The data generated by the RestaurantInspectionsETL does not have headers. However, the schema can be defined and set when the data is loaded.

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var schema = @"

INSPECTIONTYPE string,

CODES string,

CRITICALFLAG int,

INSPECTIONSCORE int,

GRADE string" ;



DataFrame df =

sc

.Read()

.Schema(schema)

.Csv(Path.Join(latestOutput, "Ungraded" ));



Define the UDF

There is no built-in function in Spark that allows you to use a PredictionEngine . However, Spark can be extended through UDFs. Keep in mind that UDFs are not optimized like the built-in functions. Therefore, whenever possible, try to use the built-in functions as much as possible.

In the Program class, create a new method called PredictGrade which takes in the set of features that make up the ModelInput expected by the trained model.

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public static string PredictGrade (

string inspectionType,

string violationCodes,

int criticalFlag,

int inspectionScore )

{

ModelInput input = new ModelInput

{

InspectionType=inspectionType,

Codes=violationCodes,

CriticalFlag=( float )criticalFlag,

InspectionScore=( float )inspectionScore

};



ModelOutput prediction = _predictionEngine.Predict(input);



return prediction.PredictedLabel;

}



Then, inside the Main method, register the PredictGrade method as a UDF in your SparkSession .

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sc.Udf().Register< string , string , int , int , string >( "PredictGrade" ,PredictGrade);



Enrich the data

Once the UDF is registered, use it inside of a Select statement which creates a new DataFrame that includes the input features as well as the predicted grade output by the trained mdoel.

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var enrichedDf =

df

.Select(

Col( "INSPECTIONTYPE" ),

Col( "CODES" ),

Col( "CRITICALFLAG" ),

Col( "INSPECTIONSCORE" ),

CallUDF( "PredictGrade" ,

Col( "INSPECTIONTYPE" ),

Col( "CODES" ),

Col( "CRITICALFLAG" ),

Col( "INSPECTIONSCORE" )

).Alias( "PREDICTEDGRADE" )

);



Finally, save the enriched DataFrame

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string outputId = new DirectoryInfo(latestOutput).Name;

string enrichedOutputPath = Path.Join(solutionDirectory, "RestaurantInspectionsEnrichment" , "Output" );

string savePath = Path.Join(enrichedOutputPath,outputId);



if (!Directory.Exists(savePath))

{

Directory.CreateDirectory(enrichedOutputPath);

}



enrichedDf.Write().Csv(savePath);



Publish and run the enrichment application

The final Program.cs file should look as follows.

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using System.IO;

using System.Linq;

using Microsoft.ML;

using Microsoft.Spark.Sql;

using static Microsoft.Spark.Sql.Functions;

using RestaurantInspectionsML;



namespace RestaurantInspectionsEnrichment

{

class Program

{

private static readonly PredictionEngine<ModelInput,ModelOutput> _predictionEngine;



static Program ( )

{

MLContext mlContext = new MLContext();

ITransformer model = mlContext.Model.Load( "model.zip" , out DataViewSchema schema);

_predictionEngine = mlContext.Model.CreatePredictionEngine<ModelInput,ModelOutput>(model);

}



static void Main ( string [] args )

{



string solutionDirectory = "/home/lqdev/Development/RestaurantInspectionsSparkMLNET" ;

string dataLocation = Path.Combine(solutionDirectory, "RestaurantInspectionsETL" , "Output" );



var latestOutput =

Directory

.GetDirectories(dataLocation)

.Select(directory => new DirectoryInfo(directory))

.OrderBy(directoryInfo => directoryInfo.Name)

.Select(directory => directory.FullName)

.First();



var sc =

SparkSession

.Builder()

.AppName( "Restaurant_Inspections_Enrichment" )

.GetOrCreate();



var schema = @"

INSPECTIONTYPE string,

CODES string,

CRITICALFLAG int,

INSPECTIONSCORE int,

GRADE string" ;



DataFrame df =

sc

.Read()

.Schema(schema)

.Csv(Path.Join(latestOutput, "Ungraded" ));



sc.Udf().Register< string , string , int , int , string >( "PredictGrade" ,PredictGrade);



var enrichedDf =

df

.Select(

Col( "INSPECTIONTYPE" ),

Col( "CODES" ),

Col( "CRITICALFLAG" ),

Col( "INSPECTIONSCORE" ),

CallUDF( "PredictGrade" ,

Col( "INSPECTIONTYPE" ),

Col( "CODES" ),

Col( "CRITICALFLAG" ),

Col( "INSPECTIONSCORE" )

).Alias( "PREDICTEDGRADE" )

);



string outputId = new DirectoryInfo(latestOutput).Name;

string enrichedOutputPath = Path.Join(solutionDirectory, "RestaurantInspectionsEnrichment" , "Output" );

string savePath = Path.Join(enrichedOutputPath,outputId);



if (!Directory.Exists(savePath))

{

Directory.CreateDirectory(enrichedOutputPath);

}



enrichedDf.Write().Csv(savePath);



}



public static string PredictGrade (

string inspectionType,

string violationCodes,

int criticalFlag,

int inspectionScore )

{

ModelInput input = new ModelInput

{

InspectionType=inspectionType,

Codes=violationCodes,

CriticalFlag=( float )criticalFlag,

InspectionScore=( float )inspectionScore

};



ModelOutput prediction = _predictionEngine.Predict(input);



return prediction.PredictedLabel;

}

}

}



From the RestaurantInspectionsEnrichment project publish the application with the following command.

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dotnet publish -f netcoreapp2.1 -r ubuntu.18.04-x64



Navigate to the publish directory. In this case, it’s bin/Debug/netcoreapp2.1/ubuntu.18.04-x64/publish.

From the publish directory, run the application with spark-submit .

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spark-submit --class org.apache.spark.deploy.dotnet.DotnetRunner --master local microsoft-spark-2.4.x-0.4.0.jar dotnet RestaurantInspectionsEnrichment.dll



The file output should look similar to the contents below:

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Cycle Inspection / Initial Inspection,04N,1,13,A

Cycle Inspection / Re-inspection,08A,0,9,A

Cycle Inspection / Initial Inspection,"10B,10H",0,10,A

Cycle Inspection / Initial Inspection,10F,0,10,A

Cycle Inspection / Reopening Inspection,10F,0,3,C



Conclusion

This solution showcased how Spark can be used within .NET applications with Spark.NET. Because it’s part of the .NET ecosystem, other components and frameworks such as ML.NET can be leveraged to extend the system’s capabilities. Although this sample was developed and run on a local, single-node cluster, Spark was made to run at scale. As such, this application can be further improved by setting up a cluster and running the ETL and enrichment workloads on there.

Resources

Apache Spark

Spark.NET

Spark.NET GitHub

Mobius

NYC OpenData