Better way of doing array Flat

Question

So I a trying to take out the objects from within an array to a new array. But I need a more better and efficient way of doing this.

this is how I did it. First I created a new array through filter1, then I flattened it and then I created another array with filter3.

filter1 = myArray.map((a => a.courseEnrolled);
filter2 = filter1.flat(1);
filter3 = filter2.map((a => a.course);

I am looking for better way of achieving same result.

    myArray = [
    {
      name: "john",
      courseEnrolled: [
        {
          course: {
            name: "react",
          },
        },
        {
          course: {
            name: "java",
          },
        },
      ],
    },
    {
      name: "Doe",
      courseEnrolled: [
        {
          course: {
            name: "java",
          },
        },
        {
          course: {
            name: "angular",
          },
        },
      ],
    },
  ];

  expectedArray = [
    {
      name: "react",
    },
    {
      name: "java",
    },
    {
      name: "java",
    },
    {
      name: "react",
    },
  ];

  uniqueExpectedArray = [
    {
      name: "react",
    },
    {
      name: "java",
    },
    {
      name: "react",
    },
  ];

well you could chain it `myArray.map((a => a.courseEnrolled).flat(1).map((a => a.course)` — Lawrence Cherone, Sep 07 '22 at 13:06
Does this answer your question? [Most efficient way to flatten Array | T> in JavaScript](https://stackoverflow.com/questions/57476260/most-efficient-way-to-flatten-arrayarrayt-t-in-javascript) — jeremy-denis, Sep 07 '22 at 13:07

score 1 · Answer 1 · answered Sep 07 '22 at 13:10

Use a flatMap() with a nested map() to get all the name's

Then get all the unique values, and use map() to convert to the final object

myArray = [{name: "john", courseEnrolled: [{course: {name: "react", }, }, {course: {name: "java", }, }, ], }, {name: "Doe", courseEnrolled: [{course: {name: "java", }, }, {course: {name: "angular", }, }, ], }, ];
    
const all = myArray.flatMap(e => e.courseEnrolled.map(c => c.course.name));
const res =  all.filter((v, i, s) => s.indexOf(v) === i).map(name => ({ name }));
console.log(res)

[
  {
    "name": "react"
  },
  {
    "name": "java"
  },
  {
    "name": "angular"
  }
]

score 0 · Answer 2 · answered Sep 07 '22 at 13:23

Use this :

expectedArray = myArray.map(a => a.courseEnrolled.map((c) => c.course)).flat(4)
uniqueArray = [...new Set(expectedArray.map(c => c.name))].map((c)=>{  return { "name" : c} })

I hope this answer helps you! Comment if you have any questions or doubts.

score 0 · Answer 3 · answered Sep 07 '22 at 13:26

Lodash, if you don't mind

const  myArray = [{name: "john",courseEnrolled: [{course: {name: "react"}},{course: {name: "java"}}]},{name: "Doe",courseEnrolled: [{course: {name: "java"}},{course: {name: "angular"}}]}];

const result = _(myArray)
  .flatMap(({ courseEnrolled }) => courseEnrolled.map(({ course }) => course))
  .uniqBy('name');
  
console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0 }

<script src="https://cdn.jsdelivr.net/npm/lodash@4.17.21/lodash.min.js"></script>

score 0 · Answer 4 · answered Sep 07 '22 at 13:43

Another solution. Kind of one-liner

const myArray = [{name: "john",courseEnrolled: [{course: {name: "react"}},{course: {name: "java"}}]},{name: "Doe",courseEnrolled: [{course: {name: "java"}},{course: {name: "angular"}}]}];

const result = Object.values(myArray.reduce((acc, { courseEnrolled: arr }) => (
  arr.forEach(({ course })=> (acc[course.name] ??= course)), acc
), {}));

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0 }

Better way of doing array Flat

4 Answers4