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in command line use ::::> cat using_avg.js | mongo

inside the using_avg.js file is:

use agg
db.products.aggregate([
    {$group:
     {
	 _id: {
	     "category":"$category"

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private class Article {

    private final String title;
    private final String author;
    private final List<String> tags;

    private Article(String title, String author, List<String> tags) {
        this.title = title;
        this.author = author;
        this.tags = tags;

oreillyross

cursor = db.students.aggregate( 
  [ { "$unwind": "$scores" },  
    {"$match": {"scores.type": "homework"}},
	{"$group": { '_id':'$_id' , 'minitem': {'$min': "$scores.score" }}}
	
  ] );
 
  db.students.update({'_id':19},{'$pull':{'scores':{'score':49.43132782777443}}})

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GET   /clients/:id          controllers.Clients.show(id: Long)

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	val a = 1 //> a  : Int = 1
	val b = 2 //> b  : Int = 2

  // Common mistakes with pattern matching
  // the lower case variable pattern needs backwards quotes to work.
  
	def oneOrTwo(i: Int): String = i match {
		case `a` => "One!"
		case `b` => "Two!"
	} //> oneOrTwo: (i: Int)String

oreillyross

Vectors are created analogously to Lists

val nums = New Vector(1,2,56,-87)

instead of List cons operator x :: xs use x +: xs or xs:+ x

Seq is a base class of List and Vector

Seq itself is a sub class of Iterable

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def sum(x: Int)(y: Int)(z: Int) = x + y + z

val curriedWithMultipleArguments = sum _

val addToNine = curriedWithMultipleArguments(4,5)

addToNine(3)

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// Sum ints
def sum(ints: List[Int]): Int = ints.foldLeft(0)((a,b) => a + b)
def sum(ints:List[Int]): Int = ints.foldLeft(0)(_+_)


// find average from a list of Double
def average(list: List[Double]): Double =
  list.foldLeft(0.0)(_+_) / list.foldLeft(0.0)((r,c) => r+1)
 
def average(list: List[Double]): Double = list match {

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object RunLengthEncoding extends App {
	
	val data = List("a","a", "a", "b","b", "a", "c", "c", "c")
	
	def pack[T](vals: List[T]): List[List[T]] = vals match {
		case Nil => Nil
		case x :: xs1 => 
		  val (first, rest) = vals span (y => y == x)
		  first :: pack(rest)
	}

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object ListFunctions extends App {
   
	val nums = List(2,-4,5,6,-3)
	
	// map function
	println(nums map (f => f > 0))
	
	// filter function
	println(nums filter (f => f > 0))