Tag Archives: Azure Databricks

Feature Engineering with PySpark in Azure Databricks

Azure Databricks is a very cool easy to use platform for both analytics engineers and machine learning developers. I would like to use this post to summarize basic APIs and tricks in feature engineering with Azure Databricks. Previously I was using Jupyter notebook or PyCharm to develop or practice some machine learning cases. Compared to Jupyter Notebook, Azure Databricks provides similar Notebook, which adds some additional features. In the future I will describe how to use Azure Databricks for production.

Feature engineering is the preprocessing phase in machine learning, also needs huge effort from developers to get data ready for modeling and training. Here I list some basic feature engineering scenarios with PySpark in Azure Databricks.

If you want to run code snippet below in normal Jupyter Notebook, you need add Spark initialization code as below. (Not necessary in Azure Databricks, as it is already for use.)

spark = SparkSession\

Continuous Data

from __future__ import print_function
from pyspark.sql import SparkSession
from pyspark.ml.feature import Binarizer

continuousDataFrame = spark.createDataFrame([
(0, 1.1),
(1, 8.5),
(2, 5.2)
], ["id", "feature"])

binarizer = Binarizer(threshold=5.1, inputCol="feature", outputCol="binarized_feature")

binarizedDataFrame = binarizer.transform(continuousDataFrame)

print("Binarizer output with Threshold = %f" % binarizer.getThreshold())
from pyspark.ml.feature import Bucketizer

splits = [-float("inf"), -0.5, 0.0, 0.5, float("inf")]
data = [(-999.9,), (-0.5,), (-0.3,), (0.0,), (0.2,), (999.9,)]
dataFrame = spark.createDataFrame(data, ["features"])

bucketizer = Bucketizer(splits=splits, inputCol="features", outputCol="bucketedFeatures")

# Assign buckets per the splits boundary
bucketedData = bucketizer.transform(dataFrame)

print("Bucketizer output with %d buckets" % (len(bucketizer.getSplits())-1))
from pyspark.ml.feature import QuantileDiscretizer

data = [(0, 18.0), (1, 19.0), (2, 8.0), (3, 5.0), (4, 2.2), (5, 9.2), (6, 14.4)]
df = spark.createDataFrame(data, ["id", "hour"])
df = df.repartition(1)

# Divide into 3 buckets as quantile distribution
discretizer = QuantileDiscretizer(numBuckets=3, inputCol="hour", outputCol="result")
discretizerModel = discretizer.fit(df)
result = discretizerModel.transform(df)
from pyspark.ml.feature import MaxAbsScaler
from pyspark.ml.linalg import Vectors

dataFrame = spark.createDataFrame([
(0, Vectors.dense([1.0, 0.1, -8.0]),),
(1, Vectors.dense([2.0, 1.0, -4.0]),),
(2, Vectors.dense([4.0, 10.0, 8.0]),)
], ["id", "features"])

scaler = MaxAbsScaler(inputCol="features", outputCol="scaledFeatures")

# Calculate Max value model
scalerModel = scaler.fit(dataFrame)

# Transform with scale model, so that values are scaled between [-1.0, 1.0]
scaledData = scalerModel.transform(dataFrame)
scaledData.select("features", "scaledFeatures").show()
#Standard scaler
from pyspark.ml.feature import StandardScaler

dataFrame = spark.read.format("libsvm").load("data/mllib/sample_libsvm_data.txt")
scaler = StandardScaler(inputCol="features", outputCol="scaledFeatures",
withStd=True, withMean=False)

# Calculate mean and variance
scalerModel = scaler.fit(dataFrame)

# Standardize
scaledData = scalerModel.transform(dataFrame)
#Polynomial expansion
from pyspark.ml.feature import PolynomialExpansion

df = spark.createDataFrame([
(Vectors.dense([2.0, 1.0]),),
(Vectors.dense([0.0, 0.0]),),
(Vectors.dense([3.0, -1.0]),)
], ["features"])

polyExpansion = PolynomialExpansion(degree=3, inputCol="features", outputCol="polyFeatures")
polyDF = polyExpansion.transform(df)


Discrete Data

# StringIndexer and One-hot encoder
from pyspark.ml.feature import OneHotEncoder, StringIndexer

df = spark.createDataFrame([
(0, "a"),
(1, "b"),
(2, "c"),
(3, "a"),
(4, "a"),
(5, "c")
], ["id", "category"])

stringIndexer = StringIndexer(inputCol="category", outputCol="categoryIndex")
model = stringIndexer.fit(df)
indexed = model.transform(df)

encoder = OneHotEncoder(inputCol="categoryIndex", outputCol="categoryVec")
encoded = encoder.transform(indexed)


#Use Stop Words
from pyspark.ml.feature import StopWordsRemover

sentenceData = spark.createDataFrame([
(0, ["I", "saw", "the", "red", "balloon"]),
(1, ["Mary", "had", "a", "little", "lamb"])
], ["id", "raw"])

remover = StopWordsRemover(inputCol="raw", outputCol="filtered")
# Tokenizer
from pyspark.ml.feature import Tokenizer, RegexTokenizer
from pyspark.sql.functions import col, udf
from pyspark.sql.types import IntegerType

sentenceDataFrame = spark.createDataFrame([
(0, "Hi I heard about Spark"),
(1, "I wish Java could use case classes"),
(2, "Logistic,regression,models,are,neat")
], ["id", "sentence"])

tokenizer = Tokenizer(inputCol="sentence", outputCol="words")

regexTokenizer = RegexTokenizer(inputCol="sentence", outputCol="words", pattern="\\W")

countTokens = udf(lambda words: len(words), IntegerType())

tokenized = tokenizer.transform(sentenceDataFrame)
tokenized.select("sentence", "words")\
.withColumn("tokens", countTokens(col("words"))).show(truncate=False)

regexTokenized = regexTokenizer.transform(sentenceDataFrame)
regexTokenized.select("sentence", "words") \
.withColumn("tokens", countTokens(col("words"))).show(truncate=False)
# Count Vectorizer
from pyspark.ml.feature import CountVectorizer

df = spark.createDataFrame([
(0, "a b c".split(" ")),
(1, "a b b c a".split(" "))
], ["id", "words"])

cv = CountVectorizer(inputCol="words", outputCol="features", vocabSize=3, minDF=2.0)
model = cv.fit(df)
result = model.transform(df)
from pyspark.ml.feature import HashingTF, IDF, Tokenizer

sentenceData = spark.createDataFrame([
(0.0, "Hi I heard about Spark"),
(0.0, "I wish Java could use case classes"),
(1.0, "Logistic regression models are neat")
], ["label", "sentence"])

tokenizer = Tokenizer(inputCol="sentence", outputCol="words")
wordsData = tokenizer.transform(sentenceData)

hashingTF = HashingTF(inputCol="words", outputCol="rawFeatures", numFeatures=20)
featurizedData = hashingTF.transform(wordsData)

idf = IDF(inputCol="rawFeatures", outputCol="features")
idfModel = idf.fit(featurizedData)
rescaledData = idfModel.transform(featurizedData)

rescaledData.select("label", "features").show()
# NGram
from pyspark.ml.feature import NGram

#Hanmeimei loves LiLei
#LiLei loves Hanmeimei

wordDataFrame = spark.createDataFrame([
(0, ["Hi", "I", "heard", "about", "Spark"]),
(1, ["I", "wish", "Java", "could", "use", "case", "classes"]),
(2, ["Logistic", "regression", "models", "are", "neat"])
], ["id", "words"])

ngram = NGram(n=2, inputCol="words", outputCol="ngrams")

ngramDataFrame = ngram.transform(wordDataFrame)


# SQL Transformer
from pyspark.ml.feature import SQLTransformer
df = spark.createDataFrame([
(0, 1.0, 3.0),
(2, 2.0, 5.0)
], ["id", "v1", "v2"])

sqlTrans = SQLTransformer(
statement="SELECT *, (v1 + v2) AS v3, (v1 * v2) AS v4 FROM __THIS__")
# R formula transform
from pyspark.ml.feature import RFormula
dataset = spark.createDataFrame(
[(7, "US", 18, 1.0),
(8, "CA", 12, 0.0),
(9, "NZ", 15, 0.0)],
["id", "country", "hour", "clicked"])

formula = RFormula(
formula="clicked ~ country + hour",

output = formula.fit(dataset).transform(dataset)
output.select("features", "label").show()

Note that: There are many feature engineering APIs are not mentioned here. Please see more info from latest pyppark.ml.feature package.



Batch Data Ingest with Azure Databricks

In the previous blog we have introduced basic steps of data ingest of streaming data with Azure Databricks. Now we are going to describe how to do batch ingest with Azure Data Bricks. Most of the steps are similar, just the spark DataFrame API are different.

Data Source

  "your blob account key here.blob.core.windows.net",
  "your blob account key value here")
val df = spark.read.json("wasbs://yout container@your blob account.blob.core.windows.net/veracity_ai_prod_41f11b1f17bb43d49ba51beabf2dd0a9/Availability/2018-06-04/06")
val availabilitySchema = df.schema

Please note that we need to df.schema to get availability log’s schema, similar for other log formar, e.g. page views, event. It is very hard to program the schema manually.

Data Transform

Use spark.read to get the Data Frame from input data. Please pay attention to input file format. inputPath/2018-05-30/09 should be matched like (inputPath + “/*/*/”)

val availabilityDF = spark.read.schema(availabilitySchema)
.option("maxFilesTrigger", 1).json(inputPath + "/*/*/")

Use Spark SQL to do the transform, much easier than transform with Data Frame API.

val sqlDF = spark
.sql("SELECT internal.data.id as ID, availability[0].testTimestamp as timestamp, availability[0].testName as name, availability[0].runLocation as location, availability[0].message as message, availability[0].durationMetric.value as duration FROM logs")

Data Sink

Here we use Azure SQL Server as the persistence of transformed data.

First define the database configuration

val jdbcUsername = "Your SQL Server username"
val jdbcPassword = "Your SQL Server password"
val jdbcHostname = "Your SQL Server name.database.windows.net" //typically, this is in the form or servername.database.windows.net
val jdbcPort = 1433
val jdbcDatabase ="Availability"
val driver = "com.microsoft.sqlserver.jdbc.SQLServerDriver"
val jdbcUrl = s"jdbc:sqlserver://${jdbcHostname}:${jdbcPort};database=${jdbcDatabase};user=${jdbcUsername};password=${jdbcPassword}"

Setup connection properties for JDBC

import java.util.Properties

val connectionProperties = new Properties()
connectionProperties.put("user", s"${jdbcUsername}")
connectionProperties.put("password", s"${jdbcPassword}")
val driverClass = "com.microsoft.sqlserver.jdbc.SQLServerDriver"
connectionProperties.setProperty("Driver", driverClass)

Finally use write.jdbc api to persistence transformed data into Azure SQL Server, quite cool.

sqlDF.write.jdbc(jdbcUrl, "aiavailability3", connectionProperties)


Recently I am working on platform analytics solution for veracity.com, the open industry data platform from DNV GL. Data Ingest is one essential part for the whole data analytics end to end flow.

Application Insights(AI) logs are one of the key data source, hence we need build streaming analytics solution for such real time data source. Here we take availability logs data as example, you can also use other  AI data sources (PageViews….).

Export the data

There is a nice document for enabling the continues export from Application Insights.

Create a storage account

When you are creating it, I suggest to use “Standard-LRS“ with Cold tier. This is simply because we use storage account as a temporary storage place. (We will move into VERACITY container for storage in production)

Configure the export settings

In this case, we are exporting one type:

  • Availability (One way for in production monitoring data)

Once it is done and the telemetry data started exporting, you should be able to see folders in the blob container in storage account. One folder is mapping to one data type in above export setting.

Take a closer look at the folder content. Below screenshot shows the PageViews data between 12am to 1pm on 28th of Sept.

Please note that:

  • The date and time are UTC and are when the telemetry was deposited in the store – not the time it was generated.
  • The folders under Availability are stored in yyyy-mm-dd/hh/ structure.
  • Each blob is a text file that contains multiple ‘\n’-separated rows.
  • It contains the telemetry processed over a time period of roughly half a minute. It means that each folder will have about 100 to 120 files.
  • Each row represents a telemetry data point such as a request or page view.
  • Each row is an JSON document. The detailed data structure can be found at here.

With the nice Azure Storage Account Explorer, it is pretty easy to check the content of the blob file.

Please note that Application Insights also implemented the same logic as IP Anonymizationin Google Analytics. For all IP address that is collected by Application Insights, last octagon is anonymized to 0 (you can see the highlighted in above screenshot).

Read the data from blob

They are many ways to transfer the data out from storage account. Here we are going to use Azure Databricks.

Add one Azure Databricks service following here.

Add one cluster, choose the basic one following here.

Add one notebook:  named for example: Streaming Data Ingest

In order Azure Databricks can read data from blob storage, there are two ways: Databricks directly read blob storage through HDFS API; Or mount blob storage container into Databricks file system. See more information about how to access Blob Storage as here. We choose the second one.

Mount the storage folder into Databricks file system(DBFS), to mount a Blob storage container or a folder inside a container, use the following command:

  source = "wasbs://<your-container-name>@<your-storage-account-name>.blob.core.windows.net/<your-directory-name>",
  mountPoint = "/mnt/export",
  extraConfigs = Map("<conf-key>" -> "<conf-value>"))

Then you can check the folder data with command:

%fs ls /mnt

Initialize SparkSession:

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

val spark = SparkSession

import spark.implicits._

In Spark 2.0+, we prefer use Structured Streaming(DataFrame /DataSet API) in, rather than Spark Core API, but when we see the Availability log data, it is XML like format, with several hierarchy. This is not easy to programming define the Structure type. The tricks here is that we first read one blob file to get Schema, then use this Schema when we create the structured streaming.

"<your key>")
val df = spark.read.json("wasbs://<your container>@<your-storage-account-name>.core.windows.net/veracity_ai_prod_41f11b1f17bb43d49ba51beabf2dd0a9/Availability/2018-06-04/06")
val availabilitySchema = df.schema

Using structured streaming here to access the files in blob folder, we are going to emulate a stream from them by reading one file at a time, in the chronological order they were created.

//Use file sink to store output data into blob storage again.
val inputPath = "/mnt/export"
val outputPath = "/mnt/output"
val streamingInput = spark.readStream.schema(availabilitySchema).option("maxFilesTrigger", 1).json(inputPath + "/*/*/")

Transform the data

Note that we do not need all availability data fields for analytics. Here we only pickup the fields that you need, as below (Needed fields are highlighted)

We use SQL to do the transform, then convert the DataFrame into DataSet, suggested if you need to do more analytics afterwards. In Structured Streaming, query is a handle to the streaming query that is running in the background.

val sqlDF = spark.sql("SELECT internal.data.id as ID, availability[0].testTimestamp as timestamp, availability[0].testName as name, availability[0].runLocation as location, availability[0].message as message, availability[0].durationMetric.value as duration FROM logs")
val sqlDS = sqlDF.as[(String, String, String, String, String, Double)]
val query2 = 
.option("path", outputPath)
.option("checkpointLocation", outputPath + "/checkpoint/")

Check the output folder in blob, to make sure that files are handled one by one continously (in micro-batch).

Note that: By the time writing this article, Structured Streaming does not support JDBC sink natively. Hence we need to extend the JDBCSink by ourselves.