科特林聚合操作
原文:https://www.geeksforgeeks.org/kotlin-aggregate-operations/
聚合操作是对数据结构(如数组)作为一个整体执行的操作，而不是对单个元素执行的操作。
-
count() 函数用于返回元素个数。 sum() 函数用于返回数字集合中元素的和。 min() 函数用于返回最小的元素。 max() 函数用于返回最大的元素。 average() 函数用于返回数字集合中元素的平均值。 maxBy() 函数返回一个 Collector，它根据给定的。 minBy() 函数返回一个 Collector，它根据给定的。 maxWith() 函数取一个 Comparator 对象，一般返回最大的元素。 minWith() 函数取一个 Comparator 对象，一般返回最小的元素。 sumBy() 通过使用线性代数和矩阵包功能，执行有效且可选的加权分组求和.. sumByDouble() Returns the sum of all values produced by selector function applied to each element in the array..
使用一些聚合函数的柯特林程序–
```kt //Functions that used aggregate operations fun main(args: Array
) { val numbers = listOf(6,34,57,78,12,4,5,5) println("Count the number of element in the list: ${numbers.count()}") println("Sum of the elements in the list: ${numbers.sum()}") println("Min value in the list: ${numbers.min()}") println("Max value in the list: ${numbers.max()}") println("Average of all elements in the list: ${numbers.average()}") } ```
输出:
```kt Count the number of element in the list: 8 Sum of the elements in the list: 201 Min value in the list: 4 Max value in the list: 78 Average of all elements in the list: 25.125
```
使用 sumBy()和 sumByDouble()函数的 Kotlin 程序-
kt //Functions that used aggregate operations fun main(args: Array<String>) { val numbers = listOf(6,34,57,78,12,4,5,5) println("Multiply each element with 3 and sum: "+numbers.sumBy { it * 3 }) println(numbers.sumByDouble { it.toDouble() / 2 }) }输出:
```kt Multiply each element with 3 and sum: 603 100.5
```
使用 minBy()和 maxWith()函数的 Kotlin 程序–
```kt //Functions that used aggregate operations fun main(args: Array
) { val numbers = listOf(6,34,57,78,12,4,5,5) val minRem = numbers.minBy { it % 4} println("Minimum remainder returned by: " +minRem) val strings = listOf("Cricket","Football","Volley","Chess") val maxstrln = strings.maxWith(compareBy { it.length }) println("String with max length is: " +maxstrln) } ```
输出:
```kt Minimum remainder returned by: 12 String with max length is: Football
```
折叠和缩小函数
- fold()函数:它以一个关联二元运算符函数为参数，将使用它来折叠集合中的元素。。
- foldRight()功能:其工作方式类似于 fold()。遍历集合中元素的顺序是从右到左。
- foldIndexed()函数:用于迭代时获取当前索引的访问权。
- foldrigendeddexed()函数:它的工作方式类似于 foldIndexed()。遍历集合中元素的顺序是从右到左
- reduce()函数将数组缩减为单个值。它为数组的每个值执行一个提供的函数。
- reduceRight()函数:其工作方式类似于 reduce()。移除集合中元素的顺序是从右到左。
- reduceIndexed()函数从第一个元素开始累加值，从左到右对当前累加器值和给定集合中每个元素及其索引应用[运算]。
- reduceRightIndexed()函数:它的工作方式类似于 reduceIndexed()。集合中的顺序是从右到左。
使用 fold()和 reduce()函数的 Kotlin 程序–
kt //Fold and Reduce Functions fun main(args: Array<String>) { val numbers = listOf(57,78,12,4,5,5, 42) val sum = numbers.reduce { sum, element -> sum + element } println("The sum of all elements in list "+sum) val sumThrice = numbers.fold(0) { sum, element -> sum + element * 3} println("Multiply each element with 3 and sum "+sumThrice) }输出:
```kt The sum of all elements in list 203 Multiply each element with 3 and sum 609
```
使用 foldRight()函数的 Kotlin 程序–
kt //Fold and Reduce Functions fun main(args: Array<String>) { val numbers = listOf(6,34,57,78,12,4,5,5, 4) val sumThriceRight= numbers.foldRight(0){element, sum -> sum + element*3} println("The sum of the numbers from the right side: "+sumThriceRight) }输出:
kt The sum of the numbers from the right side: 615使用文件夹索引()和文件夹索引()的柯特林程序–
```kt //Fold and Reduce Functions fun main(args: Array
) { val numbers = listOf(6,34,57,78,12,4,5,5, 42, 10, 4) val sumOfEvenNumbers = numbers.foldIndexed(0) { idx, sum, element -> if (idx % 2 == 0) sum + element else sum } println("Sum of even numbers: "+sumOfEvenNumbers) val sumOfEvenFromRight = numbers.foldRightIndexed(0) { idx, element, sum -> if (idx % 2 == 0) sum + element else sum } println("Sum of even numbers from Right side: "+sumOfEvenFromRight) } ```
输出:
```kt Sum of even numbers: 126 Sum of even numbers from Right side: 126
```
