Given an array that nests inner objects which have key-value pairs, I want to convert single-element-arrays to just the value itself.

So let's say that we have the following albums array:

const albums = [
    {
        "band": ["beetles"],
        "album": ["yellow_submarine"],
        "year": [1969]
    },
    {
        "band": [ "coldplay"],
        "album": ["Parachutes"],
        "year": [2000]
    },
    {
        "band": ["nirvana"],
        "album": ["nevermind"],
        "year": [1991]
    }
]

Since all the arrays are single-values, I would like to convert this entire albums object to:

// desired output
[
    {
        "band": "beetles",
        "album": "yellow_submarine",
        "year": 1969
    },
    {
        "band": "coldplay",
        "album": "Parachutes",
        "year": 2000
    },
    {
        "band": "nirvana",
        "album": "nevermind",
        "year": 1991
    }
]

I've seem lots of posts discussing the opposite (i.e., how to convert a single value into an array), but could not find an answer to this current question. Maybe I'm not using the correct search terms...

CodePudding user response：

If you want to create a new array of new objects, you'd use map along with creating new objects unwrapping their values. You have a couple of options for how to handle the objects. You could use Object.fromEntries and Object.entries:

const updatedAlbums = albums.map(album =>
    Object.fromEntries(
        Object.entries(album).map(([key, value]) => [key, value[0]])
    )
);

Live Example:

const albums = [
    {
        "band": ["beetles"],
        "album": ["yellow_submarine"],
        "year": [1969]
    },
    {
        "band": [ "coldplay"],
        "album": ["Parachutes"],
        "year": [2000]
    },
    {
        "band": ["nirvana"],
        "album": ["nevermind"],
        "year": [1991]
    }
];

const updatedAlbums = albums.map(album =>
    Object.fromEntries(
        Object.entries(album).map(([key, value]) => [key, value[0]])
    )
);

console.log(updatedAlbums);

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

Or you could use an inner loop to avoid intermediary arrays:

const updatedAlbums = albums.map(album => {
    const newAlbum = {};
    for (const key in album) {
        if (Object.hasOwn(album, key)) {
            newAlbum[key] = album[key][0]; // Unwrapping the value
        }
    }
    return newAlbum;
});

Live Example:

const albums = [
    {
        "band": ["beetles"],
        "album": ["yellow_submarine"],
        "year": [1969]
    },
    {
        "band": [ "coldplay"],
        "album": ["Parachutes"],
        "year": [2000]
    },
    {
        "band": ["nirvana"],
        "album": ["nevermind"],
        "year": [1991]
    }
];

// Quick-and-dirty polyfill for environments that don't have `Object.hasOwn` yet
if (!Object.hasOwn) {
    Object.hasOwn = Function.prototype.call.bind(Object.prototype.hasOwnProperty);
}

const updatedAlbums = albums.map(album => {
    const newAlbum = {};
    for (const key in album) {
        if (Object.hasOwn(album, key)) {
            newAlbum[key] = album[key][0]; // Unwrapping the value
        }
    }
    return newAlbum;
});

console.log(updatedAlbums);

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

CodePudding user response：

Map albums to a new array of objects, use a unArray method within the map -lambda

const albums = [{
    "band": ["beetles"],
    "album": ["yellow_submarine"],
    "year": [1969]
  },
  {
    "band": ["coldplay"],
    "album": ["Parachutes"],
    "year": [2000]
  },
  {
    "band": ["nirvana"],
    "album": ["nevermind"],
    "year": [1991]
  }
];

// Note: for a true copy of albums and its arrays,
// the values must be spreaded (e.g. ...album.band)
const noArrays = albums.map(album => {
  const unArray = v => v.length === 1 ? v.shift() : v;
  return { ...{},
    band: unArray(...album.band),
    album: unArray(...album.album),
    year: unArray(...album.year)
  };
});

console.log(noArrays);

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

If the keys of the albums entries are not (all) known, using a reducer for all album entries would be more generic:

const albums = [{
    "band": ["beetles"],
    "album": ["yellow_submarine"],
    "year": [1969]
  },
  {
    "band": ["coldplay"],
    "album": ["Parachutes"],
    "year": [2000]
  },
  {
    "band": ["nirvana"],
    "album": ["nevermind"],
    "year": [1991]
  }
];

// Note: for a true copy of albums and its arrays,
// the values ust be spreaded (i.e ...value)
const noArrays = albums.map( album => {
  const unArray = v => v.length === 1 ? v.shift() : v;
  return Object.entries(album).reduce( (acc, [key, value]) => 
    ({...acc, [key]: unArray(...value)}), {});
});

console.log(noArrays);

CodePudding user response：

Edit: This changes the value in place rather than creating a new dictionary with the final result.

for (var i = 0; i < albums.length; i  ) {
   for (var key in albums[i]) {
      albums[i][key] = albums[i][key][0];
   }
}

CodePudding user response：

Keep it Simple! You can achieve this by just using Array.toString() method.

Working Demo :

const albums = [
    {
        "band": ["beetles"],
        "album": ["yellow_submarine"],
        "year": [1969]
    },
    {
        "band": [ "coldplay"],
        "album": ["Parachutes"],
        "year": [2000]
    },
    {
        "band": ["nirvana"],
        "album": ["nevermind"],
        "year": [1991]
    }
];

albums.forEach((obj) => {
    Object.keys(obj).forEach((key) => {
    obj[key] = obj[key].length === 1 ? obj[key].toString() : obj[key]
  });
});

console.log(albums);