Create Scala Project using SBT and Jar using sbt-assembly

1. Download and install SBT - http://www.scala-sbt.org/download.html
2. Create SBT Scala Project by running this command - sbt new sbt/scala-seed.g8
3. When prompted for the project name, type HelloWorld. This will create a new project under a directory named HelloWorld.
4. Run the sample application by access HelloWorld folder, type sbt, compile and run.
   
5. Add sbt-assembly as a dependency in project/assembly.sbt
   addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.14.5")
6. Type assembly.
   
7. Now you'll have an awesome new assembly task which will compile your project, run your tests, and then pack your class files and all your dependencies into a single JAR file: target/scala_X.X.X/projectname-assembly-X.X.X.jar.
8. Type java -jar target/scala_X.X.X/projectname-assembly-X.X.X.jar to run the program.

References:

http://www.scala-sbt.org/download.html

https://github.com/sbt/sbt-assembly

JavaScript Evolution ECMAScript 6 - Function with Default Parameter

In ES2015, a developer can add a default parameter into a function. Example:

function loadProfile(usernames=[]){
  if (usernames.lenght > 3){
    let loadingMessage ="This will take a while.";
  }
}

With default parameter, you can call the function either

loadProfile(['Simon','Alex','Arlene']);

Or

loadProfile();

Scala has more powerful default parameter. Let's create Scala function with default parameter.

def addInt(a:Int=5, b:Int=7) = {
  var sum: Int = a + b;
  return sum
}

You can call the function by passing the parameter using a pointer.

addInt(b=10)

Passing parameter using pointer is not implement in JavaScript.

Scala map vs flatMap

map is loop thru all element and apply a function into it.

scala> val i = List("Apple", "Banana", "Orange")
i: List[String] = List(Apple, Banana, Orange)

scala> i.map(x => x.toUpperCase)
res2: List[Char] = List(APPLE, BANANA, ORANGE)

flatMap is loop thru all element, flatten the element and apply a function into it.

scala> val i = List("Apple", "Banana", "Orange")
i: List[String] = List(Apple, Banana, Orange)

scala> i.flatMap(x => x.toUpperCase)
res2: List[Char] = List(A, P, P, L, E, B, A, N, A, N, A, O, R, A, N, G, E)

Here is an example on different between map and flatMap in List(List(), List())

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

scala> def x(v:Int) = List(v,v+1)
x: (v: Int)List[Int]

scala> l.map(i => x(i))
res5: List[List[Int]] = List(List(1, 2), List(2, 3), List(3, 4))

scala> l.flatMap(i => x(i))
res6: List[Int] = List(1, 2, 2, 3, 3, 4)

Here is an example on different between map and flatMap in Option (None and Some). flatMap remove empty value (None).

scala> val l = List(1,2,3,4,5)
l: List[Int] = List(1, 2, 3, 4, 5)

scala> def f(x:Int) = if (x > 2) Some(x) else None
f: (x: Int)Option[Int]

scala> l.map( x => f(x))
res11: List[Option[Int]] = List(None, None, Some(3), Some(4), Some(5))

scala> l.flatMap( x => f(x))
res12: List[Int] = List(3, 4, 5)

References:
http://www.brunton-spall.co.uk/post/2011/12/02/map-map-and-flatmap-in-scala/
http://alvinalexander.com/scala/collection-scala-flatmap-examples-map-flatten

Scala For Loop Syntax

For Loop with Counter

The simplest loop syntax is:

for (a  <- 1 to 5){
   println(“Print a: ” + a);
}




When the above code is compiled and executed, it produces following result:

Print a: 1
Print a: 2
Print a: 3
Print a: 4
Print a: 5

By default, counter increment is 1. You can change the number of counter increment using "by".

for (a  <- 1 to 5 by 2) {
   println(“Print a: ” + a);
}

When the above code is compiled and executed, it produces following result:

Print a: 1
Print a: 3
Print a: 5

For Loop with Filter

You can filter out some of the elements. Following is the example of for loop along with filters:

for (
   a  <- 1 to 5
   if ( a > 3)
) {
   println(“Print a: ” + a);
}

When the above code is compiled and executed, it produces following result:

Print a: 4
Print a: 5

For Loop with Yield

This is one of the awesome feature in Scala where you generate a static type variable using loop. I don’t really see in other programming language.

When For loop finishes running, it returns a collection of all these yielded values.

The type of the collection that is returned is the same type that you were iterating over.

// Loop through and generate a variable
val i = for (
   a  <- 1 to 5
   if ( a > 3)
) yield {
   a
}

// Print the result
for( a <- i){
   println( "Value of a: " + a );
}

When the above code is compiled and executed, it produces following result:

Print a: 4
Print a: 5

A great scala introduction with all available tools for developer

http://assist-software.net/blog/awesome-scala

Using Scala Recursion Functions For Permutation Calculation

Permutation is an ordered combination - how many possible ordered combination.

There are 2 types of Permutation:

1. Permutation with Repeat is Allowed
   
   Permutation Lock is an example of Repeat Allowed.
   
   There are 10 numbers to choose from (0,1,...9) and we choose 3 of them.
   
   10 x 10 x 10 = 1000 permutation
   
   
   

   Formula: nr where n is the number of things to choose from, and r 
   is number of times

2. Permutation with No Repeat
   
   
   
   A good example is lottery which number can not be repeat.
   
   There are 3 numbers to choose from (1,2 and 3) and we choose 3 of them.
   
   3 x 2 x 1 = 6 permutation
   
   

   Formula: Without repetition our choices get reduced each time.

But how do we write that mathematically? Answer: we use the "factorial function".

I am going to use recursion method to write factorial function. This program accepts 2 integer inputs (Number of things to choose from and Number of times to choose) and calculate how many permutation (possible combination) with not repeat.

object Permutations {
  def main(args: Array[String]) {
    print("How many lottery number? ")
    val num1 = readInt()
    println()
    print("How many lottery  number to pick? ")
    val num2 = readInt()
    println("Total Permutation: " + factorial(num1,num2).toString)
  }
  
  def factorial(x: BigInt, y: BigInt) : BigInt = {
    if (y > 1)
      x * factorial( x - 1, y - 1)
    else
      x
  }
}

1. Tips: Remember to has exist call on recursive function to avoid unstopped loop