/*
    Notes on Collections

    By default, Scala uses immutable collections. However, there are mutable
    versions available (in the scala.collection.mutable package). The most common
    collections are List, Set, and Map.
*/

// Declaring a set
val urls = Set("google.com", "yahoo.com", "nytimes.com")

//
// Matching values in a set with filter(). filter(Boolean) allows you to iterate through
// a collection to verify whether a value should be filtered in or out (based on a boolean)
// statement
//
// mkString() is another method from Iterable that creates a flat representation
// of the collection and calls each objects toString method.
//
// Output: matching URLs: google.com, yahoo.com
val ooUrls = urls filter (_ contains "oo")
println("matching URLs: " + ooUrls.mkString(", "))

//
// Intersection
// Output: The intersection is: google.com, yahoo.com
val urls2 = Set("yahoo.com", "twitter.com", "google.com", "amazon.com")
val intersection = urls ** urls2
println("The intersection is: " + intersection.mkString(", "))

//
// Merge
// Output: The merge is: amazon.com, google.com, yahoo.com, nytimes.com, twitter.com
val merge = urls ++ urls2
println("The merge is: " + merge.mkString(", "))

//
// map(f(A) => B) will apply the function f to each element of a collection and
// return B
// Output: E-mails: help@google.com, help@yahoo.com, help@nytimes.com
val helpEmails = urls map ("help@" + _)
println("E-mails: " + helpEmails.mkString(", "))

// Another example of map, this time using a def'd method and passing it to
// map.
// Output: E-mails: help@google.com, help@yahoo.com, help@nytimes.com
def fn(a : String) : String = {
	"help@" + a
}
val helpEmails2 = urls map fn
println("E-mails: " + helpEmails2.mkString(", "))

//
// find(p : (A) => Boolean) : Option[A]
val found = urls find (_ contains "google")
val oo = urls find (_ contains "oo")
println(found)
println(oo)

/*
// Folding
// This section is pretty interesting. Using the fnFoldLeft and fnFoldRight methods,
// I found that the order of parameters matters for folding. if foldRight is
// executed with fnFoldLeft, the number passed into 'total' parameter will be
// the value pulled out of the list.
//
// In some cases, the foldRight will appear not to work if the parameters of
// the method are out of order
//
// It is also important to keep in mind that folding may be affected by the
// order of operations. Lists are ordered, buts sets are not and so iterating
// over a set with positive and negative numbers could produce unexpected results.
*/

val nums = List(1,2,3,4,2)
println(nums)
println("Left Concat is: " + nums.foldLeft("")
	{ (str, item) => str + item.toString() } )
println("Right Concat is: " + nums.foldRight("")
	{ (item, str) => str + item.toString() } )

val nums2 = List(-1,2,-3,4,-5,6)

def fnFoldLeft(total : Int, num : Int) : Int = {
	println(total.toString() + " - " + num.toString())
	total - num
}
def fnFoldRight(num : Int, total : Int) : Int = {
	println(total.toString() + " - " + num.toString())
	total - num
}
println("foldLeft:")
println(nums2.foldLeft(0)(fnFoldLeft))
println("foldRight:")
println(nums2.foldRight(0)(fnFoldRight))