[置顶] 【scala 代码片段3】轻松入门scala--集合的操作交并补

主要内容：

1、集合的过滤filter

2、集合的集合flatten

3、集合的交并补diff、intersect、union、distinct

4、flatMap、Map用法

5、集合条件检查

6、集合分组 partition

7、foldLeft求和

代码片段：

/**
* Created by Administrator on 2017/1/13.
*/
object student {
def main(args: Array[String]) {

//    过滤过集合
val numbers = Seq(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
val a = numbers.filter(n => n % 2 == 0)
val b = numbers.filter(_ % 2 == 0)
println(a)
println(b)

//然后加大难度，我想获取页数大于120页的书。
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 c = books.filter(book => book.pages >= 120)
println(c)

//当有一个集合的集合，然后你想对这些集合的所有元素进行操作时，就会用到 flatten。
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)
val d = alphabet.flatten
println(d)

val num1 = Seq(1, 2, 3, 4, 5, 6)
val num2 = Seq(4, 5, 6, 7, 8, 9)
//List(1, 2, 3)
//    只在第一个序列出现
println(num1.diff(num2))
//List(4, 5, 6)
//    两个集合的交集
println(num1.intersect(num2))
//    两个集合的并集去重
//List(1, 2, 3, 4, 5, 6, 4, 5, 6, 7, 8, 9)
println(num1.union(num2).distinct)

//  map（映射）列表元素
val numbers101 = Seq(1, 2, 3, 4, 5, 6)
//List(2, 4, 6, 8, 10, 12)
println(numbers101.map(m => m * 2))
val chars = Seq('a', 'b', 'c', 'd')
//List(A, B, C, D)
println(chars.map(ch => ch.toUpper))

// flatMap
val abcd2 = Seq('a', 'b', 'c', 'd')
//List(A, a, B, b, C, c, D, d)
val abcd3 = abcd2.flatMap(ch => List(ch.toUpper, ch))
println(abcd3)

//对整个集合进行条件检查
val numbers1 = Seq(3, 7, 2, 9, 6, 5, 1, 4, 2)
println(numbers1.forall(m => m < 10))
println(numbers1.forall(m => m > 5))

//partition 对集合进行分组
val numbers3 = Seq(3, 7, 2, 9, 6, 5, 1, 4, 2)
//(List(2, 6, 4, 2), List(3, 7, 9, 5, 1))
val number2 = numbers3.partition(n => n % 2 == 0)
println(number2)

//   foldLeft
val words = Seq("apple", "dog", "table")
println(words.foldLeft(0)((resultLength, word) => resultLength + word.length))

}
}

运行结果：

List(2, 4, 6, 8, 10)
List(2, 4, 6, 8, 10)
List(Book(Parallel algorithms,240), Book(Object Oriented Programming,130), Book(Mobile Development,495))
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)
List(1, 2, 3)
List(4, 5, 6)
List(1, 2, 3, 4, 5, 6, 7, 8, 9)
List(2, 4, 6, 8, 10, 12)
List(A, B, C, D)
List(A, a, B, b, C, c, D, d)
true
false
(List(2, 6, 4, 2),List(3, 7, 9, 5, 1))
13

Process finished with exit code 0