问题描述

我是一名新开发人员，似乎无法弄清楚如何在布尔数组中找到 True 语句的数量.我知道如何按索引而不是按值查找.任何帮助将不胜感激.

I am a new developer and cannot seem to figure out how to find the number of True statements in an Array of Booleans. I know how to find by index but not by value. Any assistance would be appreciated.

let arrayElement = [Bool](repeating: false, count: 10)
var before: [[Bool]] = [[Bool]](repeating: arrayElement, count:10)
for i in 0 ..< 10 {
    for j in 0 ..< 10 {
        if arc4random_uniform(3) == 1 {
            before[i][j] = true  
        }        
    }
}

推荐答案

条目数的方法

一种方法是过滤您的 Bool 元素数组(对于 true)并简单地计算过滤后数组中剩余元素的数量

entriesina1Darray

One method would be to filter your array of Bool elements (for true) and simply count the number of remaining elements in the filtered array

let arr = [false, true, true, false, true]
let numberOfTrue = arr.filter{$0}.count
print(numberOfTrue) // 3

另一种方法是reduce(展开)数组并为每个等于true

Another approach is to reduce (unfold) the array and increment a counter for each element that equals true

let arr = [false, true, true, false, true]
let numberOfTrue = arr.reduce(0) { $0 + ($1 ? 1 : 0) }
print(numberOfTrue) // 3

或者，传统的 for 循环(带有条件循环签名)方法，与 reduce 方法相当:

Or, a traditional for loop (with conditional in loop signature) approach, comparable top the reduce method:

let arr = [false, true, true, false, true]
var trueCounter = 0
for bElem in arr where bElem { trueCounter += 1 }
print(trueCounter) // 3

实现一维数组

通过简单地应用 .joined() 在 [[Bool]] 数组上依次构造一个 [Bool] 数组.

toachievea1Darray

The methods above can easily be applied to an array of arrays (of Bool elements: type [[Bool]]) by simply applying .joined() on the [[Bool]] array to sequentially construct a [Bool] array.

/* 'before' is of type [[Bool]], constructed as described
   in the question */
let numberOfTrueAlt1 = before.joined().filter{$0}.count

let numberOfTrueAlt2 = before.joined().reduce(0) { $0 + ($1 ? 1 : 0) }

var numberOfTrueAlt3 = 0
for bElem in before.joined() where bElem { numberOfTrueAlt3 += 1 }

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