如何从swift中的float数组中获取前2个最大值？

Question

我需要从float数组中获得2个最大值，即一个最高和一个最高的值。是否有任何简单的方法来获取它们的索引，或者是否需要将数组更改为此结构？

Answer 1

只是排序的数组，如果你想索引只是拿它们喜欢采取必要的值

var array1 = [2.1, 2.2, 2.5, 3.0, 4.2, 2] 

var array2 = array1.sort(){ $0 > $1} 

//One way 
let firstMax = array2[0] 
let secondMax = array2[1] 

//Second way 
let firstMax = array2.removeFirst() 
let secondMax = array2.removeFirst() 

编辑

let maxPos = array1.indexOf(firstMax) 
let secMaxPos = array1.indexOf(secondMax) 

如果您对这些事情感到困惑，请按照以下常规基础进行操作。

var max = -1.0, maxPos = -1, secMax = -1.0, secMaxPos = -1 
for (index, value) in array1.enumerate() { 
    if value > max { 
     max = value 
     maxPos = index 
    } else if value > secMax { 
     secMax = value 
     secMaxPos = index 
    } 
} 
print("max:\(max)->pos:\(maxPos)::secMax:\(secMax)->secMaxPos:\(secMaxPos)") 

Answer 2

可以使用enumerate()按值创建包含元组（指数值）的数组，然后排序该数组找到最大的两个值：

let arr: [Float] = [1.2, 3.14, 1.609, 2.718, 0.3] 

// Create an array of (index, value) tuples sorted by value 
// in decreasing order 
let result = arr.enumerate().sort { $0.1 > $1.1 } 
print(result) 

[(1, 3.1400001), (3, 2.71799994), (2, 1.60899997), (0, 1.20000005), (4, 0.300000012)] 

let (topIndex, top) = result[0] 
print("top = \(top), index = \(topIndex)") 

top = 3.14, index = 1 

let (secondIndex, second) = result[1] 
print("second = \(second), index = \(secondIndex)") 

second = 2.718, index = 3 

Answer 3

尝试在你的游戏gorund

VAR项目= 2.01，3.95,1.85,2.65,1.6]

VAR分类= item.sort（{$ 0> $ 1}）

打印（排序）

Answer 4

基本的想法是遍历数组，并挑出最大和次大的项目。

一些短码，可能是难以阅读：

let myFloatArray : [Float] = ... 
let top2 = myFloatArray.enumerated().reduce(((-1, Float.nan), (-1, Float.nan)), combine: { t, v in 
    // Check if value is larger than first item in tuple 
    if (!(v.1 <= t.0.1)) { 
     // Check if value is larger than second item in tuple 
     if (!(v.1 <= t.1.1)) { 
      // Return with new value as largest 
      return (t.1, v) 
     } else { 
      // Return with new value as next largest 
      return (v, t.1) 
     } 
    } 
    // Return old result 
    return t 
}) 

或者更明确的变量名：

var largestIndex = -1; 
var largestValue = Float.nan; 
var secondLargestIndex = -1; 
var secondLargestValue = Float.nan; 
for index in 0..<myFloatArray.count { 
    let value = myFloatArray[index]; 
    if (!(value <= secondLargestValue)) { 
     if (!(value <= largestValue)) { 
      secondLargestValue = largestValue; 
      secondLargestIndex = largestIndex; 
      largestValue = value; 
      largestIndex = index; 
     } else { 
      secondLargestValue = value; 
      secondLargestIndex = index; 
     } 
    } 
}