Push into array inside reduced new Map()-CodePudding

I am trying to push to an array on a new Map() reduce from an array of objects, but for some reason it pushes only two items per array.

const data = [
  {
    keyword: 'engines',
    url: 'google.com',
  },
  {
    keyword: 'engines',
    url: 'duckduckgo.com',
  },
  {
    keyword: 'pc',
    url: 'mac.com',
  },
  {
    keyword: 'pc',
    url: 'linux.com',
  },
  {
    keyword: 'pc',
    url: 'windows.com',
  }
]

let urls = []

const mapper = data.reduce((acc, obj) => {
  urls.push(obj.url)
  if (!acc.has(obj.keyword)) {
    acc.set(obj.keyword, urls )
  } else {
    urls = []
  }
  return acc
}, new Map())


console.log(mapper)

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Expected output

Map(2) {
  'engines' => [ 'google.com', 'duckduckgo.com'],
  'pc' => [ 'mac.com', 'linux.com', 'windows.com']
}

I dont even know why the snippet does not work on stackoverflow, it works fine on editor.

CodePudding user response：

I fixed it with this but is does not feel right

const data = [ { keyword: 'engines', url: 'google.com', }, { keyword: 'engines', url: 'duckduckgo.com', }, { keyword: 'pc', url: 'mac.com', }, { keyword: 'pc', url: 'linux.com', }, { keyword: 'pc', url: 'windows.com', } ]

let urls = []

const mapper = data.reduce((acc, obj) => {
 
  if (!acc.has(obj.keyword)) {
    urls = []
  } 

  urls.push(obj.url)
  
  acc.set(obj.keyword, urls )
  return acc
}, new Map())


console.log(mapper)

CodePudding user response：

This gives you the correct output.

You need to use a new array for each keyword; otherwise you're sharing a single object and corrupting it as you go.

StackOverflow's REPL does not output Map content in the same way as browsers when using console.log, so I used a workaround to display the data.

const data = [
  {
    keyword: 'engines',
    url: 'google.com',
  },
  {
    keyword: 'engines',
    url: 'duckduckgo.com',
  },
  {
    keyword: 'pc',
    url: 'mac.com',
  },
  {
    keyword: 'pc',
    url: 'linux.com',
  },
  {
    keyword: 'pc',
    url: 'windows.com',
  }
]

const mapper = data.reduce((acc, obj) => {
  if (!acc.has(obj.keyword)) {
    acc.set(obj.keyword, [] )
  }
  let urls = acc.get(obj.keyword)
  urls.push(obj.url);
  return acc;
}, new Map())

/**
Expected output per OP:
Map(2) {
  'engines' => [ 'google.com', 'duckduckgo.com'],
  'pc' => [ 'mac.com', 'linux.com', 'windows.com']
}
*/
console.log([...mapper.entries()])

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