在具有不同值（数组）的对象数组中查找对象的最有效方法是什么？

Question

I initially got this question in an interview few months back & have gotten around to solve it now.

So we have this array of objects & the goal is to find an an object with actors that haven't appeared in a movie more than once. So basically find a movie with unique actors.

[
  {
    name: 'The Dark Knight',
    rating: 'PG-13',
    year: 2012,
    bestScene: {
      name: 'fight',
      location: 'sewer',
      sceneLength: 10,
      actors: ['Christian Bale', 'Tom Hardy']
    }
  },
  {
    name: 'Good Burger',
    rating: 'PG',
    year: 1994,
    bestScene: {
      name: 'jump',
      location: 'giant milkshake',
      sceneLength: 5,
      actors: ['Kenan Thompson', 'Kel Mitchell']
    }
  },
  {
    name: 'Sharknado 2: The Second One',
    rating: 'TV-14',
    year: 2013
  },
  {
    name: 'The Big Short',
    rating: 'R',
    year: 2015,
    bestScene: {
      name: 'explanation',
      location: 'casino',
      sceneLength: 20,
      actors: ['Christian Bale', 'Steve Carrell']
    }
  }
]

And a goal I have set for myself is to solve it using functional way so naturally we need to weed out objects with no bestScene present like this:

const moviesWithActorsPresent = movies.filter((movie) => movie.bestScene)

I could then use reduce to construct an array of objects like this:

[
  { 'The Dark Knight': [ 'Christian Bale', 'Tom Hardy' ] },
  { 'Good Burger': [ 'Kenan Thompson', 'Kel Mitchell' ] },
  { 'The Big Short': [ 'Christian Bale', 'Steve Carrell' ] }
]

And then loop through using for or forEach & keep track of the actors in a temporary variable but that to me is not exactly an elegant solution.

What CS concept we can use here to solve it efficiently?

Answer 1

Once you have the moviesWithActorsPresent , create an object (or Map) counting up the number of occurrences of each actor in the entire array. Then you can .find an object for which .every actor has a count of exactly 1:

 const movies =[ { name: 'The Dark Knight', rating: 'PG-13', year: 2012, bestScene: { name: 'fight', location: 'sewer', sceneLength: 10, actors: ['Christian Bale', 'Tom Hardy'] } }, { name: 'Good Burger', rating: 'PG', year: 1994, bestScene: { name: 'jump', location: 'giant milkshake', sceneLength: 5, actors: ['Kenan Thompson', 'Kel Mitchell'] } }, { name: 'Sharknado 2: The Second One', rating: 'TV-14', year: 2013 }, { name: 'The Big Short', rating: 'R', year: 2015, bestScene: { name: 'explanation', location: 'casino', sceneLength: 20, actors: ['Christian Bale', 'Steve Carrell'] } } ]; const moviesWithActorsPresent = movies.filter((movie) => movie.bestScene) const actorCounts = moviesWithActorsPresent.reduce((a, { bestScene }) => { const { actors } = bestScene; return Object.assign( {}, // don't mutate a, // prior counts ...actors.map(actor => ({ [actor]: (a[actor] || 0) + 1 })) ); }, {}); const movieWithUniqueActors = moviesWithActorsPresent.find(({ bestScene }) => ( bestScene.actors.every(actor => actorCounts[actor] === 1) )); console.log(movieWithUniqueActors);

It almost certainly doesn't matter, but you can put the .filter functionality into the .reduce if you want:

 const movies = [{ name: 'The Dark Knight', rating: 'PG-13', year: 2012, bestScene: { name: 'fight', location: 'sewer', sceneLength: 10, actors: ['Christian Bale', 'Tom Hardy'] } }, { name: 'Good Burger', rating: 'PG', year: 1994, bestScene: { name: 'jump', location: 'giant milkshake', sceneLength: 5, actors: ['Kenan Thompson', 'Kel Mitchell'] } }, { name: 'Sharknado 2: The Second One', rating: 'TV-14', year: 2013 }, { name: 'The Big Short', rating: 'R', year: 2015, bestScene: { name: 'explanation', location: 'casino', sceneLength: 20, actors: ['Christian Bale', 'Steve Carrell'] } } ]; const actorCounts = movies.reduce((a, { bestScene }) => { if (!bestScene) { return a; } const { actors } = bestScene; return Object.assign({}, // don't mutate a, // prior counts ...actors.map(actor => ({ [actor]: (a[actor] || 0) + 1 })) ); }, {}); const movieWithUniqueActors = movies.find(({ bestScene }) => ( bestScene.actors.every(actor => actorCounts[actor] === 1) )); console.log(movieWithUniqueActors);

Answer 2

You'd just need to create a function which groups films by actors , and then take only those that have 1 film.

 const group = (data) => data .reduce((res, { name, bestScene }) => { ((bestScene || {}).actors || []).forEach(actor => { res[actor] = (res[actor] || []).concat(name); }); return res; }, {}); const solve = data => Object .entries(group(data)) .filter(([author, films]) => films.length === 1) const data = [ { name: 'The Dark Knight', rating: 'PG-13', year: 2012, bestScene: { name: 'fight', location: 'sewer', sceneLength: 10, actors: ['Christian Bale', 'Tom Hardy'] } }, { name: 'Good Burger', rating: 'PG', year: 1994, bestScene: { name: 'jump', location: 'giant milkshake', sceneLength: 5, actors: ['Kenan Thompson', 'Kel Mitchell'] } }, { name: 'Sharknado 2: The Second One', rating: 'TV-14', year: 2013 }, { name: 'The Big Short', rating: 'R', year: 2015, bestScene: { name: 'explanation', location: 'casino', sceneLength: 20, actors: ['Christian Bale', 'Steve Carrell'] } } ]; console.log(solve(data));