Scala的一些操作

ゝ一世哀愁。 2023-07-09 10:26 156阅读 0赞

## Scala的一些操作 ##

### 一、Map操作 ###

map操作是针对集合的典型变换操作，它将某个函数应用到集合中的每个元素，并产生一个结果集合。

//    生成1到10的list
        val l1 = (1 to 10).toList
        println(l1)

**1.求给定集合数字的两倍的集合**

**(1)写法1**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70][]

**(2)写法2**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 1][]

**2.求给定集合数字的平方**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 2][]

**3.将集合的数字乘以2后再平方，最后求和**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 3][]

### 二、filter操作 ###

**1.将大于10的元素取出。**

val l1 = (1 to 10).toList
    val l2 = l1.map(_*2).filter(_>10)
    println(l1)
    println(l2)

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 4][]

### 三、reduce操作 ###

我们可以使用reduce这种二元操作对集合中的元素进行归约。

**1.对list的数据进行求和**

val list = List(1,2,3,4,5)
        println(list.reduce(_+_))

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 5][]

整个加法操作的执行顺序如下：

1+2 = 3
    3+3 = 6
    6+4 = 10
    10+5 = 15

### 四、fold操作 ###

折叠(fold)操作和reduce（归约）操作比较类似。fold操作需要从一个初始的“种子”值开始，并以该值作为上下文，处理集合中的每个元素。

**1.对list的数据进行求和**

val list = List(1,2,3,4,5)
        println(list.fold(10)(_+_))

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjgzMDY5Nw_size_16_color_FFFFFF_t_70 6][]

整个加法操作的执行顺序如下：

10+1=11
    11+2=13
    13+3=16
    16+4=20
    20+5=25

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