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H2O.ai: Learn to Use the KMeans Algorithm

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Consumer trends and choices play a key role in enterprise strategies. Analysing huge volumes of customer data is not feasible manually. Hence, enterprises lean heavily on machine learning. H2O.ai is open source software for Big Data analysis. This article discusses the implementation of the KMeans algorithm with H2O.ai.

Most enterprises are taking a lot of interest in machine learning (ML) techniques, which help us use historical data to make better business decisions. ML algorithms discover patterns in data and construct mathematical models based on these discoveries. Such models can then be used to predict the occurrence of events of significance at some future date. As an example, if we have information about our customers (like name, age, address, financial position, marital status, etc), it would be possible to group them. Based on this grouping, it would be possible to gauge the probability of the identified group purchasing the new products that an enterprise may be ready to launch.
For any ML technique to be successful, it needs quality data and that too in volume. Till the arrival of Big Data technologies that allowed enterprises to crunch huge volumes of data in a distributed manner using commodity hardware, most machine learning techniques used sample data sets. These sets allowed ML algorithms to generate reasonably accurate results. But, as is well known, an inference is only as good as the data from which it is derived. Thus, it is preferable to derive inferences from the complete data set, instead of relying on sample data.
Using Big Data tools like Hadoop, the open source community created the Apache Mahout ML library. This library allows the execution of ML algorithms across huge volumes of data using commodity hardware. As enterprises grew more comfortable with and realised the importance of ML, they demanded high performance algorithms that would be able to process voluminous data, but also to do so at speed. This is one of the key drivers for applications like H2O.ai, developed by 0xdata (pronounced ‘hexadata’).

What is H2O?
H2O is an open source, in-memory application for machine learning. It does in-memory analytics on clusters, with distributed parallelised machine learning algorithms. By using in-memory data, it is able to perform compute-intensive operations at speed and deliver results much faster than other popular tools like Apache Mahout. H2O can be deployed as a standalone application on the Hadoop platform and on Amazon EC2. For storing data, it uses the main memory of the server on which it executes. In case of Hadoop, it can use HDFS as a data store. For the Amazon space, it can use Amazon S3.
As speed is one of the unique selling points (USP) of H2O, we decided to test its performance.
Considering that we had a customer segmentation solution implementation using the KMeans algorithm provided by Apache Mahout, we wanted to compare its performance with the KMeans implementation provided by H2O. While H2O documentation provides information about the KMeans algorithm, I was not able to locate suitable examples that would allow me to execute it on a test data set. I was able to execute the algorithm on the test data using the H2O user interface (known as Flow), but this method was obviously not scalable as it cannot be integrated easily with enterprise applications. For this purpose, I wanted to invoke the algorithm from a Java application, enabling easier integration with enterprise applications.

Using the KMeans algorithm
I searched for samples that would show me Let’s Try use the library, but with little success. Finally, a colleague found an example written in Scala, which was part of the Sparkling Water library (a new library being developed by combining Apache Spark and H2O libraries). I have mapped the Scala source code to Java and have added a print statement that displays the result of the clustering (this part was missing from the sample). The sample application is shown in the following sections.

The main method
In the main method of the sample (as depicted in Snippet 1), we need to set up the H2O instance, which in this case will be on the local machine (standalone mode of H2O, one node cluster).

// Setup cloud name
String[] args = new String[]
// Build a cloud of 1
H2O.waitForCloudSize(1, 10*1000);

Snippet 1: The main method

Parsing the data
After creating the cluster, we need to read the data. The data is an input file, in the CSV format, containing numerical information. One line of the input represents one record. Each record represents information for one customer. Thus, the input file represents the customers we wish to group into clusters using the KMeans algorithm. As depicted in Snippet 2, the file is read into a vector of values and parsed into the Frame object.

NFSFileVec nfs = NFSFileVec.make(f);
Frame frame = water.parser.ParseDataset.parse(Key.make(),nfs._key);

Snippet 2: Parsing the data

Initialising the KMeans algorithm
After parsing the data, we set up the KMeans algorithm. In this case, we created five clusters and the number of iterations for algorithm execution was 1000. This is depicted in Snippet 3.

KMeansParameters params = new KMeansParameters();
params._k = 5;
params._max_iterations = 1000;

Snippet 3: Configuring the algorithm

Training the algorithm and executing it
Now, we have to create the KMeans model using the specified parameters. We then execute the algorithm by running the score method of the KMeansModel object. The score method executes the KMeans algorithm on the specified data (stored in the frame vector). The output of the algorithm is stored in another Frame object, named output, as depicted in Snippet 4. It is important to note that the Frame objects are stored in the memory by H2O.

// create the model
KMeans job = new KMeans(params);
// train the model
KMeansModel kmm = job.trainModel().get();
// execute the model on the loaded data
Frame output = kmm.score(frame);

Snippet 4: Creating the model and scoring it

Displaying the results
After execution, the results are available in the output variable. In order to display which customer record belongs to which cluster, we need to access the vecs variable from the output variable. In this sample, we are printing the result on the screen. The vector vecs contains as many records as were present in the input file. Each entry mentions the ID of the cluster into which the customer record has been placed, as depicted in Snippet 5.

Vec[] vecs = output.vecs();
for ( Vec v : vecs ) {
System.out.println(v + “, “ + v.length());
for ( int i = 0; i < v.length(); i++ ) {
System.out.println(i + “: “ + v.at(i));
}
}
System.out.println();

Snippet 5: Displaying the cluster ID for each record

The complete sample
The complete sample is presented below.

/* Using KMeans from the H2O.ai library */
import hex.kmeans.KMeans;
import hex.kmeans.KMeansModel;
import hex.kmeans.KMeansModel.KMeansParameters;
import java.io.File;
file:///D:/SVN/TechCoE/Team 5/Publish/external/2015/Using H2O k...
3 of 4 29-Sep-15 11:46 AM
import water.H2O;
import water.Key;
import water.fvec.Frame;
import water.fvec.NFSFileVec;
import water.fvec.Vec;
public class H2OKMeans
{
public static void initialize()
{
// Setup cloud name
String[] args = new String[] { “-name”, “h2o_kmeans_test”};
// Build a cloud of 1
H2O.main(args);
H2O.waitForCloudSize(1, 10*1000 /* ms */);
}
public static void runKMeans()
{
File f = new File(“data-for-kmeans.csv”);
NFSFileVec nfs = NFSFileVec.make(f);
Frame frame = water.parser.ParseDataset.parse(Key.make(),nfs._key);
KMeansParameters params = new KMeansParameters();
params._train = frame._key;
params._k = 5;
params._max_iterations = 1000;
KMeans job = new KMeans(params);
KMeansModel kmm = job.trainModel().get();
Frame output = kmm.score(frame);
Vec[] vecs = output.vecs();
System.out.print(“vecs: “);
for ( Vec v : vecs ) {
System.out.println(v + “, “ + v.length());
for ( int i = 0; i < v.length(); i++ ) {
System.out.println(i + “: “ + v.at(i));
}
}
System.out.println();
}
public static void main(String[] args) throws Exception
{
initialize();
runKMeans();
System.exit(0);
}
}
/* end */