Question

我想知道为什么这段代码错误Cannot read property 'odd' of undefined：

var numbers = [5, 3, 8, 6, 9, 1, 0, 2, 2];

let isOdd = function(number){
    return number % 2 !== 0;
}

var oddEvenCounts = numbers.reduce(function(counts, number) {
    let odd;
    let even;

    if (isOdd(number)) {
        counts[odd] = counts['odd'] + 1;
    } else {
        counts[even] = counts['even'] + 1;
    }
 }, {});

console.log(oddEvenCoutns(numbers));

// expected result
// counts = {
//   odd: 1,
//   even: 3
// }

你看到错误在哪里吗？它基本上指向计数[奇数]和计数[偶数]

Answer 1

如果您想计算列表numbers中的赔率和赔率数，那么我要么误解您的意图，要么您的预期输出错误。

// expected result
// counts = {
//   odd: 1,
//   even: 3
// }

当你的数组中有9个数字时没有意义。但是，我认为这个问题最适合作为mapreduce问题。因为您正在将相同的函数isOdd应用（映射）到数组中的每个元素，然后将其减少为单个对象。

let numbers = [5, 3, 8, 6, 9, 1, 0, 2, 2];

// good job, this looks fine! +1 strict equality operator
const isOdd = function(number) {
    return number % 2 !== 0;
}

// function to keep track of your odd and evens 
const sumEvenOdd = function(acc, cur) {
    if (true == cur) {
        acc['odd'] += 1;
    } else {
        acc['even'] += 1;
    }
    return acc; // make sure you return your resulting object so it doesn't lose scope!
}

let foo = numbers.map( el => isOdd(el) ) // determine even or odd
                 .reduce( sumEvenOdd,  {'even': 0,'odd': 0}); // sum even and odd!
console.log(foo); // {'even': 5, 'odd': 4}

Answer 2

试试这个，你需要返回计数

var numbers = [5, 3, 8, 6, 9, 1, 0, 2, 2];
function isOddNumber(number){
    return number % 2 !== 0;
}

var oddEvenCounts = numbers.reduce(function(counts, number) {
    let odd;
    let even;
    if(isOddNumber()){
        console.log(number)
        counts['odd'] = number + 1;
    } else {
    counts['even'] = number + 1;
    }
    return counts;
}, {});
console.log(oddEvenCounts); // this is not a function it holds the value from reduce

Answer 3

逐步mapreduce

let numbers = [5, 3, 8, 6, 9, 1, 0, 2, 2];

function is_odd(number) { return number % 2 !== 0; }

function get_counts(numbers) {
    numbers = numbers.map(is_odd);                                            // map is_odd over xs -> [true, true, false, false, true, true, false, false, false]
    let odd_sum = numbers.reduce(function(sum, n) { return sum + n; }, 0);    // reduce sum of true values -> 4

    return { 'odd': odd_sum, 'even': numbers.length - odd_sum }
}

console.log(get_counts(numbers));

Answer 4

var numbers = [5, 3, 8, 6, 9, 1, 0, 2, 2];
var oddEvenCounts = numbers.reduce(function(counts, number) {
  if (isOdd(number)) {
    counts.odd++;
  } else {
    counts.even++;
  }
  return counts;
}, {odd: 0, even: 0});

function isOdd(number) {
  return number % 2 === 1;
}

console.log(oddEvenCounts); // { "odd": 4, "even": 5 }

找到错误是奇怪的

4 个答案: