Read an HDFS file functional way in scala

This example reads an HDFS file in scala in a functional manner. We use Stream class to read data lazily when required.

val path = new Path("/data/abc.csv")

val conf = new Configuration()

val fileSystem = FileSystem.get(conf)

val stream = fileSystem.open(path)

// Important to make this def, bcoz if we make it val the memory might bloat up as it keeps the old

// values in the stream as well

def readLines = Stream.cons(stream.readLine, Stream.continually( stream.readLine))

readLines.takeWhile(_ != null).foreach(line => println(line))

Learning Scala

Reading : http://twitter.github.io/scala_school/

def f1(x : Int) : Int = x+1

def fact( z: Int) : Int = z* fact(z-1)

Anonymous functions
-------------------
scala> val addOne = (x: Int) => x + 1
addOne: (Int) => Int = <function1>

scala> addOne(1)
res4: Int = 2

def timesTwo(i: Int): Int = {
  println("hello world")
  i * 2
}

Partial application
-------------------

scala> def adder(m: Int, n: Int) = m + n
adder: (m: Int,n: Int)Int

scala> val add2 = adder(2, _:Int)
add2: (Int) => Int = <function1>

scala> add2(3)
res50: Int = 5

Curried functions
-----------------

scala> def multiply(m: Int)(n: Int): Int = m * n
multiply: (m: Int)(n: Int)Int


You can take any function of multiple arguments and curry it.

scala> val curriedAdd = (adder _).curried
curriedAdd: Int => (Int => Int) = <function1>

scala> val addTwo = curriedAdd(2)
addTwo: Int => Int = <function1>

scala> addTwo(4)
res22: Int = 6


Variable length arguments
-------------------------

def capitalizeAll(args: String*) = {
  args.map { arg =>
    arg.capitalize
  }
}

scala> capitalizeAll("rarity", "applejack")
res2: Seq[String] = ArrayBuffer(Rarity, Applejack)


Classes
-------

scala> class Calculator {
     |   val brand: String = "HP"
     |   def add(m: Int, n: Int): Int = m + n
     | }
defined class Calculator

scala> val calc = new Calculator
calc: Calculator = Calculator@e75a11



http://jim-mcbeath.blogspot.in/2009/05/scala-functions-vs-methods.html