使用Javascript在数组中嵌套对象值的总和

Question

我想得到运动的总和。我正在尝试获取两个 Course 数组元素的总和。** 尝试对单个数组元素使用 reduce 方法，但无法得到总和。 我尝试了 forOf 和 forIn 循环，但我无法解决这个问题。

const courses = [
{
  name: "Half Stack application development",
  id: 1,
  parts: [
    {
      name: 'Fundamentals of React',
      exercises: 10,
      id: 1
    },
    {
      name: 'Using props to pass data',
      exercises: 7,
      id: 2
    },
    {
      name: 'State of a component',
      exercises: 14,
      id: 3
    },
    {
      name: 'Redux',
      exercises: 11,
      id: 4
    }
  ]
}, 
{
  name: "Node",
  id: 2,
  parts: [
    {
      name: 'Routing',
      exercises: 3,
      id: 1
    },
    {
      name: 'Middleware',
      exercises: 7,
      id: 2
    }
  ]
}

]

Answer 1

您可以结合使用map 和reduce 来获得每门课程的锻炼总数。

const courses = [
{
  name: "Half Stack application development",
  id: 1,
  parts: [
    {
      name: 'Fundamentals of React',
      exercises: 10,
      id: 1
    },
    {
      name: 'Using props to pass data',
      exercises: 7,
      id: 2
    },
    {
      name: 'State of a component',
      exercises: 14,
      id: 3
    },
    {
      name: 'Redux',
      exercises: 11,
      id: 4
    }
  ]
}, 
{
  name: "Node",
  id: 2,
  parts: [
    {
      name: 'Routing',
      exercises: 3,
      id: 1
    },
    {
      name: 'Middleware',
      exercises: 7,
      id: 2
    }
  ]
}
]

const sum = courses.reduce((acc, course) => {
  acc[course.name] = course.parts.reduce((acc, el) => acc + el.exercises, 0);
  return acc;
}, {});

console.log(sum);

Answer 2

想想步骤，这里有提示：

1. 先总结每门课程的练习
2. 总结所有课程的所有练习

1。每门课程的总结练习

这里的想法是为每门课程创建一个新的练习计数数组

exercises_courses = courses.map(item => {
  item.parts.reduce((sum, part) => sum + part.exercises, 0)
})

2。总结所有练习

all_exercises = exercises_courses.reduce((sum, exercises_course) => sum + exercises_course, 0)

console.log(all_exercises)