Spark Extension : ML transformers, SQL aggregations, etc that are missing in Apache Spark
Scala
Latest commit d0c8cc2 Jan 25, 2016 @ezhulenev ezhulenev Merge pull request #17 from collectivemedia/add-miminum-support-trans…
…formation

Add index/support transformation for gather encoder

README.md

Spark Ext

Build Status

Spark ML transformers, estimator, Spark SQL aggregations, etc that are missing in Apache Spark.

That's how we are doing Audience Modeling at Collective

Where to get it

resolvers += "Collective Media Bintray" at "https://dl.bintray.com/collectivemedia/releases"

And use following library dependencies:

libraryDependencies +=  "com.collective.sparkext" %% "sparkext-sql" % "0.0.23"
libraryDependencies +=  "com.collective.sparkext" %% "sparkext-mllib" % "0.0.23"

Testing

sbt test

Spark SQL

val schema = StructType(Seq(
  StructField("cookie_id", StringType),
  StructField("site", StringType),
  StructField("impressions", LongType)
))

val impressionLog = sqlContext.createDataFrame(sc.parallelize(Seq(
  Row("cookie_1", "google.com", 10L),
  Row("cookie_2", "cnn.com", 14L),
  ...
)), schema)

CollectArray

Aggregation function that collects all values from a column

import org.apache.spark.sql.ext.functions._

// collects all sites for cookie (with duplicates)
impressionLog
      .groupBy(col("cookie_id"))
      .agg(collectArray(col("site")))

Spark ML

S2 Geometry CellId transformer

Gets Google S2 Geometry CellId from decimal lat and lon

val schema = StructType(Seq(
   StructField("city", StringType),
   StructField("lat", DoubleType),
   StructField("lon", DoubleType)
 ))

 val cities = sqlContext.createDataFrame(sc.parallelize(Seq(
   Row("New York", 40.7142700, -74.0059700),
   Row("London", 51.50722, -0.12750),
   Row("Princeton", 40.3487200, -74.6590500)
 )), schema)

  val s2CellTransformer = new S2CellTransformer().setLevel(6)
  s2CellTransformer.transform(cities)

Optimal Binning

Continuous features may need to be transformed to binary format using binning to account for nonlinearity. In general, binning attempts to break a set of ordered values into evenly distributed groups, such that each group contains approximately the same number of values from the sample.

Gather

Inspired by R tidyr and reshape2 packages. Convert long DataFrame with values for each key into wide DataFrame, applying aggregation function if single key has multiple values

cookie_id site_id impressions
cookieAA 123 10
cookieAA 123 5
cookieAA 456 20
val gather = new Gather()
      .setPrimaryKeyCols("cookie_id")
      .setKeyCol("site_id")
      .setValueCol("impressions")
      .setOutputCol("sites")
val gathered = gather.transform(siteLog)      
cookie_id sites
cookieAA [{ site_id: 123, impressions: 15.0 }, { site_id: 456, impressions: 20.0 }]

Gather Encoder

Encode categorical key-value pairs using dummy variables.

cookie_id sites
cookieAA [{ site_id: 1, impressions: 15.0 }, { site_id: 2, impressions: 20.0 }]
cookieBB [{ site_id: 2, impressions: 7.0 }, { site_id: 3, impressions: 5.0 }]

transformed into

cookie_id site_features
cookieAA [ 15.0 , 20.0 , 0 ]
cookieBB [ 0.0 , 7.0 , 5.0 ]

Optionally apply dimensionality reduction using top transformation:

  • Top coverage, is selecting categorical values by computing the count of distinct users for each value, sorting the values in descending order by the count of users, and choosing the top values from the resulting list such that the sum of the distinct user counts over these values covers c percent of all users, for example, selecting top sites covering 99% of users.

Downsampling Negatives

If class ratio between positives and negatives is too high, you might want to downsample all you negatives before building a model.

val downsampling = new Downsampling()
      .setLabelCol("label")
      .setOutputCol("sample_weight")
      .setMaxClassRatio(30.0)
      .setPrimaryClass(1.0) // positive class to keep as-is