Grouping Arrays By Nested Arrays

Question

I have the following array that I'd like to transform into an Object with unique hobbies as the keys

const arr = [
  { name: 'Joe', hobbies: ['skating', 'biking', 'music'] },
  { name: 'Kim', hobbies: ['fishing', 'biking', 'karate'] },
  { name: 'Ben', hobbies: ['surfing'] },
]

I use lodash's handy groupBy function but it groups the multiple array elements into single keys like so

{
  'skating,biking,music': [
    { name: 'Joe' }
  ],
  'fishing,biking,karate': [
    { name: 'Kim' }
  ],
  'surfing': [
    { name: 'Ben' }
  ],
}

What I need is the following output (note the objects are repeated for each of their respective hobbies)

{
  biking: [
    { name: 'Joe' },
    { name: 'Kim' }
  ],
  skating: [
    { name: 'Joe' }
  ],
  karate: [
    { name: 'Kim' }
  ],
  surfing: [
    { name: 'Ben' }
  ],
  ...
}

Is there a simple way to group this array without looping through each array element, splitting them up and regrouping? Would like to avoid this if there's better utility method out there I'm unaware of

AlexSp3 · Accepted Answer · 2021-08-17 16:16:57Z

1

You can iterate each item and each hobbie and then add it to a result object:

const arr = [
  { name: 'Joe', hobbies: ['skating', 'biking', 'music'] },
  { name: 'Kim', hobbies: ['fishing', 'biking', 'karate'] },
  { name: 'Ben', hobbies: ['surfing'] }
]

const result = {};
arr.forEach(item => 
  item.hobbies.forEach(hobbie => 
    result[hobbie] = (result[hobbie] || []).concat({name: item.name})
  )
)

console.log(result);

answered Aug 17, 2021 at 16:16

AlexSp3

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1 Comment

Clay Banks Over a year ago

Brilliant! This works just how I need it to

shubham jha · Accepted Answer · 2021-08-17 16:25:42Z

1

const arr = [
  { name: 'Joe', hobbies: ['skating', 'biking', 'music'] },
  { name: 'Kim', hobbies: ['fishing', 'biking', 'karate'] },
  { name: 'Ben', hobbies: ['surfing'] }
]

const result = {};
arr.forEach(item => 
  item.hobbies.forEach(hobbie => 
    result[hobbie] = result[hobbie]?[...result[hobbie],{name: item.name}]: [{name: item.name}]
  )
)

console.log(result);

answered Aug 17, 2021 at 16:25

shubham jha

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Comments

Habebit · Accepted Answer · 2021-08-17 16:43:08Z

0

I've renamed arr to people for better understanding.

const people = [
  { name: 'Joe', hobbies: ['skating', 'biking', 'music'] },
  { name: 'Kim', hobbies: ['fishing', 'biking', 'karate'] },
  { name: 'Ben', hobbies: ['surfing'] },
];

function transform(people) {
  // get all hobbies and remove duplicates
  const hobbies = [... new Set(
    people.reduce((hobbies, person) => hobbies.concat(person.hobbies),  [])
  )];
  const res = {};
  // take a hobby and use it as key
  for (let hobby of hobbies) {
    res[hobby] = people
      .filter((person) => person.hobbies.includes(hobby))
      .map((person) => { return { name: person.name }; });
  }
  return res;
}

console.log(transform(people));

answered Aug 17, 2021 at 16:43

Habebit

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