Kotlin中take、drop方法使用

1、 take方法：

private fun take() {
    val mList = mutableListOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 0)
    //take函数是根据传入的参数挑出该集合【前n个元素】的子集合
    val mNewList1 = mList.take(2)
    println(mNewList1)
    //[1, 2]

    //takeLast函数是根据传入的参数挑出该集合【倒数n个元素】的子集合
    val mNewList2 = mList.takeLast(2)
    println(mNewList2)
    //[9, 0]
}

2、 takeWhile

private fun takeWhile() {
    val mList = mutableListOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 0)

    //takeWhile : 从头开始取值，不符合立即停止
    val mNewList3 = mList.takeWhile {
        it % 2 == 0
    }
    println(mNewList3)
    //[]


    //takeLastWhile : 从尾开始取值，不符合立即停止
    val mNewList4 = mList.takeLastWhile {
        it % 2 == 0
    }
    println(mNewList4)
    //[0]
}

3、 takeIf

private fun takeIf() {
    val mList = mutableListOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 0)

    //如果符合返回它
    val mNewList5 = mList.takeIf {
        it.size == 10 //true
    }
    println(mNewList5)
    //[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]


    val mNewList51 = mList.takeIf {
        it.size == 5  //false
    }
    println(mNewList51)
    //null
}

4、 takeUnless

private fun takeUnless() {
    val mList = mutableListOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 0)

    //如果不符合返回它
    val mNewList6 = mList.takeUnless {
        it.size == 10  //true
    }
    println(mNewList6)
    //null


    val mNewList61 = mList.takeUnless {
        it.size == 5  //false
    }
    println(mNewList61)
    //[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]

}

5、 drop

private fun drop() {
    //去掉前n个开始取值
    val mList = mutableListOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 0)
    val resultList = mList.drop(3)
    println(resultList)
}
//[4, 5, 6, 7, 8, 9, 0]

6、 dropLast

private fun dropLast() {
    //去掉最后n个开始取值
    val mList = mutableListOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 0)
    val resultList = mList.dropLast(3)
    println(resultList)
}
//[1, 2, 3, 4, 5, 6, 7]

7、dropLastWhile

private fun dropWhile() {
    //从头开始找不满足的开始取值，满足的抛弃头部
    val mList = mutableListOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 0)
    val resultList = mList.dropWhile { it <= 1 }
    println(resultList)
}
//[2, 3, 4, 5, 6, 7, 8, 9, 0]

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