valnumbers= Seq(1,2,3,4,5,6)
//List(2, 4, 6, 8, 10, 12)
numbers.map(n=> n * 2)
valchars= Seq('a','b','c','d')
//输出为List(A, B, C, D)
chars.map(ch=> ch.toUpper)
val abcd = Seq('a', 'b', 'c', 'd')
val efgj = Seq('e', 'f', 'g', 'h')
val ijkl = Seq('i', 'j', 'k', 'l')
val mnop = Seq('m', 'n', 'o', 'p')
val qrst = Seq('q', 'r', 's', 't')
val uvwx = Seq('u', 'v', 'w', 'x')
val yz = Seq('y', 'z')
val alphabet = Seq(abcd, efgj, ijkl, mnop, qrst, uvwx, yz)
// List(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z)
alphabet.flatten
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valabcd= Seq('a','b','c','d')
//List(A, a, B, b, C, c, D, d)
abcd.flatMap(ch=> List(ch.toUpper, ch))
scala> List(List(1,2),List(3,4)).flatMap(x=>x.map(x=>x*2))
res5: List[Int] = List(2, 4, 6, 8)
valnumbers=Seq(3,7,2,9,6,5,1,4,2)
//ture
numbers.forall(n=> n < 10)
//false
numbers.forall(n=> n > 5) 而 forall 函数就是为处理这类需求而创建的。
val numbers = Seq(1,2,3,4,5,6,7,8,9,10)
numbers.filter(n = > n % 2 == 0) //seq(2,4,6,8,10)
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case class Book(title : String, pages : Int)
val books = Seq(
Book("Future of Scala developers", 85),
Book("Parallel algorithms", 240),
Book("Object Oriented Programming", 130),
Book("Mobile Development", 495)
)
books.filter(book = > book.pages > = 120)
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val numbers = Seq(3, 7, 2, 9, 6, 5, 1, 4, 2)
//(List(2, 6, 4, 2), List(3, 7, 9, 5, 1))
numbers.partition (n = > n % 2 == 0)
//(List(Book(Parallel algorithms,240), Book(Object Oriented Programming,130)),
List(Book(Future of Scala developers,85), Book(Mobile Development,495)))
case class Book(title : String, pages : Int)
val books = Seq(
Book("Future of Scala developers", 85),
Book("Parallel algorithms", 240),
Book("Object Oriented Programming", 130),
Book("Mobile Development", 495)
)
val boo= books.partition(book =>book.pages % 2==0)
println(boo)
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valnumbers=Seq(1,2,3,4,5)
//15
numbers.foldLeft(0)((res, n) => res + n)
在第一对括号中,我们放一个起始值。 在第二对括号中,我们定义需要对数字序列的每个元素执行的操作。 第一步,n = 0,然后它根据序列元素变化。 另一个关于 foldLeft 的例子,计算字符数:val words = Seq("apple", "dog", "table")
//13
words.foldLeft(0)((resultLength, word) => resultLength + word.length)
val words = Seq("apple", "dog", "table")
//13
words.foldLeft(0)((resultLength, word) => resultLength + word.length)
val a = List(1,2,3,5,6)
val b = a.reduce(_+_) //求和21,类似a.sum
val c = a.reduce(_-_)//求差。-19
同理:(_*_) (_/_)
val b = a.reduce(_+_) //求和21,类似a.sum
val c = a.reduce(_-_)//求差。-19
同理:(_*_) (_/_)
valnumbers=Seq(11,2,5,1,6,3,9)
numbers.max//11
numbers.min//1
但实际操作的数据更加复杂。下面我们介绍一个更高级的例子,其中包含一个书的序列(查看源代码案例)。
caseclassBook(title:String, pages:Int)
valbooks=Seq(
Book("Future of Scala developers",85),
Book("Parallel algorithms",240),
Book("Object Oriented Programming",130),
Book("Mobile Development",495)
)
//Book(Mobile Development,495)
books.maxBy(book=> book.pages)
//Book(Future of Scala developers,85)
books.minBy(book=> book.pages)
val num 1 = Seq(1, 2, 3, 4, 5, 6)
val num 2 = Seq(4, 5, 6, 7, 8, 9)
//List(1, 2, 3)
num1.diff(num2)
//List(4, 5, 6)
num1.intersect(num2)
//List(1, 2, 3, 4, 5, 6, 4, 5, 6, 7, 8, 9)
num1.union(num2)
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