Category: Uncategorized

spark-submit a Python application in cluster mode

To launch a Python Spark application in cluster mode it is necessary to broadcast the application to the workers, using the --py-files directive. I concluded that the best way to do it is to create a fat egg with the .py files, and extract the entry point python file from it. The packaged code is referenced from the Spark application adding this reference in the entry point file:

import sys
sys.path.insert(0, <name of egg file>)

A simple working example can be found here:

https://github.com/sparkfireworks/spark-submit-cluster-python

Scala foldLeft

foldleft is a partial applied function (curried), where first it is applied an initial value followed by an operation on a pair of elements from the sequence to be fold:

def foldLeft[B](z: B)(op: (B, A) ⇒ B): B

scala> val xs: List[Int] = List(1,2,3)
xs: List[Int] = List(1, 2, 3)

scala> xs.foldLeft(0){(acc, x) => acc + x}
res9: Int = 6

scala> xs.foldLeft(0)(_+_)
res10: Int = 6

Scala string operations

Create an empty string:

scala> val emptyString: String = ""
emptyString: String = ""

Concatenate strings:

scala> "London " + "city"
res1: String = London city

String length:

scala> val str: String = "London " + "city"
str: String = London city

scala> str.length()
res7: Int = 11

scala> str.size
res8: Int = 11

Mulitine String:

scala> val str: String = """I am a multiline
     | String
     | In Scala""".stripMargin
str: String =
I am a multiline
String
In Scala

Parametrize a String:

scala> val name: String = "London"
name: String = London

scala> val str: String = s"""${name} city""".stripMargin
str: String = London city

Concatenate a Sequence of Strings:

scala> val xs: List[String] = List("To", "be", "or", "not", "to", "be")
xs: List[String] = List(To, be, or, not, to, be)

scala> xs.mkString(" ")
res1: String = To be or not to be