How to get the same property in all nested objects in an array?-CodePudding

How can I get all the values of the property code in nested arrays of objects? I mean, no matter how many nesting levels.

[
  {code: '1', children: [
    {code: '11'}, {code: '12'}
  ]},
  {code: '2', children: [
    {code: '21'}, {code: '22', children: [{code: '221'}]}
  ]},
]

Expected result : [1, 11, 12, 2, 21, 22, 221]

CodePudding user response：

flatMap is your friend for this, and you can combine it with a recursive function, destructuring function parameters with default value, and array rest syntax.

const flatten = arr => arr.flatMap(
  ({ code, children=[] }) => [code, ...flatten(children)])

const flatten = arr => arr.flatMap(
  ({ code, children=[] }) => [code, ...flatten(children)])


const arr = [
  { code: '1', children: [{ code: '11' }, { code: '12' }] },
  { code: '2', children: [{ code: '21' }, { code: '22', children: [{ code: '221' }] }],},
]

console.log(flatten(arr))

By the way, what you have there is a well-known data structure named tree, you should research more about it, and specially the different ways to traverse them: dfs and bfs.

CodePudding user response：

You can easily achieve this result using recursion and flatMap as:

function getCodes(arr) {
    return arr.flatMap((o) => {
        const childrenCodes = o.children ? getCodes(o.children) : [];
        return [ o.code, ...childrenCodes];
    });
}

const arr = [
    { code: '1', children: [{ code: '11' }, { code: '12' }] },
    { code: '2', children: [{ code: '21' }, { code: '22', children: [{ code: '221' }] }],},
];

function getCodes(arr) {
    return arr.flatMap((o) => {
        const childrenCodes = o.children ? getCodes(o.children) : [];
        return [ o.code, ...childrenCodes];
    });
}

console.log(getCodes(arr));

CodePudding user response：

A good example for generator function and dfs or bfs

const laziness = [{
    code: '1',
    children: [{
      code: '11'
    }, {
      code: '12'
    }]
  },
  {
    code: '2',
    children: [{
      code: '21'
    }, {
      code: '22',
      children: [{
        code: '221'
      }]
    }]
  },
]

console.log([...bfs(laziness)])
console.log([...dfs(laziness)])

// bfs
function* bfs(items) {
  const queue = [...items]
  while (queue.length) {
    const item = queue.shift()
    yield   item.code
    if (item.children) {
      queue.push(...item.children)
    }
  }
}

// dfs
function* dfs(items) {
  for (const item of items) {
    yield   item.code
    if (item.children) {
      yield* dfs(item.children)
    }
  }
}

CodePudding user response：

You can use recursion to make it work:

function getCode (nestedArray, current = []){
 nestedArray.forEach((e)=>{
  if ('code' in e) current.push(e.code)
  const keys = Object.keys(e);
  keys.forEach(k => {
   if (Array.isArray(e[k]) getCode(e[k], current);
 }
 return current;
}

getCode([
 {code: '1', children: [{code: '11'}, {code: '12'}]},
 {code: '2', children: [{code: '21'}, {code: '22', children: [{code: '221'}]}]},
])