Get unique strings from array of array of objects

Question

I have an array which contains arrays of objects. I want to get the unique property values from the array. E.g.

var array =     [
  [
    {
      a: 'ggg'
    },
    {
      a: 'kkk'
    }
  ],
  [
    {
      a: undefined
    }
  ],
  [
    {
      a: 'ddd'
    }
  ],
  [
    {
      a: 'ggg'
    }
  ]
];

Would return:

['ggg', 'kkk', 'ddd']

Im using the underscore library, heres what I tried:

var list = _.reduce(arr, function(memo, v, k) {
      memo.concat(_.pluck(v, 'a'));
    return memo;
}, []);

console.log('list is ', list);

console.log(_.uniq(list));

But its not working. The fiddle is here.

Gruff Bunny · Accepted Answer · 2016-11-03 14:20:04Z

4

Here's a solution using Underscore's flatten, reject, pluck and uniq:

var result = _.chain(array)
    .flatten()
    .pluck('a')
    .reject(_.isUndefined)
    .uniq()
    .value();

edited Nov 3, 2016 at 14:20

answered Nov 3, 2016 at 13:10

Gruff Bunny

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2 Comments

Mark Over a year ago

Very nice. Leaves undefined though. Adding .filter(Boolean); to the end will filter out falsey values

Gruff Bunny Over a year ago

Oops, thanks. Added a reject(_.isUndefined) to get rid of those pesky undefineds

Nina Scholz · Accepted Answer · 2016-11-03 13:11:18Z

4

With ES6, you could use Set.

var array = [[{ a: 'ggg' }, { a: 'kkk' }], [{ a: undefined }], [{ a: 'ddd' }], [{ a: 'ggg' }]],
    set = new Set();

array.forEach(a => a.forEach(b => b.a && set.add(b.a)));
console.log([...set]);

Traditional with an object.

var array = [[{ a: 'ggg' }, { a: 'kkk' }], [{ a: undefined }], [{ a: 'ddd' }], [{ a: 'ggg' }]],
    set = Object.create(null);

array.forEach(function (a) {
    a.forEach(function (b) { 
        b.a && (set[b.a] = true);
    })
});
console.log(Object.keys(set));

answered Nov 3, 2016 at 13:11

Nina Scholz

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Comments

Rajesh Dixit · Accepted Answer · 2016-11-03 13:05:29Z

0

You can loop over it and manually create an array

var array = [
  [{
    a: 'ggg'
  }, {
    a: 'kkk'
  }],
  [{
    a: undefined
  }],
  [{
    a: 'ddd'
  }],
  [{
    a: 'ggg'
  }]
];

var result = [];
array.forEach(function(a){
  a.forEach(function(obj){
    if(result.indexOf(obj.a) < 0 && obj.a)
      result.push(obj.a)
  })
})

console.log(result)

answered Nov 3, 2016 at 13:05

Rajesh Dixit

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Comments

Weedoze · Accepted Answer · 2016-11-03 13:07:17Z

0

var array = [
  [{
    a: 'ggg'
  }, {
    a: 'kkk'
  }],
  [{
    a: undefined
  }],
  [{
    a: 'ddd'
  }],
  [{
    a: 'ggg'
  }]
];

var values = [];

array.map(function(item) {
  return item.map(function(item2) {
    if(item2.a)
      values.push(item2.a);
  });
});

values = values.filter(function(v, i) {
  return values.indexOf(v) == i;
});

console.log(values);

answered Nov 3, 2016 at 13:07

Weedoze

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Comments

OliverRadini · Accepted Answer · 2016-11-03 13:07:55Z

0

I see some others have anwsered now, but here's now I did it:

https://jsfiddle.net/uc0vot3n/

var array =     [
  [
    {
      a: 'ggg'
    },
    {
      a: 'kkk'
    }
  ],
  [
    {
      a: undefined
    }
  ],
  [
    {
      a: 'ddd'
    }
  ],
  [
    {
      a: 'ggg'
    }
  ]
];

var uniq = [];

array.map(function(obj){
		obj.map(function(item){
        if (uniq.indexOf(item.a) === -1 && item.a){
    				uniq.push(item.a);
    		}
    });

});

console.log(uniq);

answered Nov 3, 2016 at 13:07

OliverRadini

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Comments

twoLeftFeet · Accepted Answer · 2016-11-03 13:23:24Z

0

Here's an alternative solution to the norm...it doesn't use indexOf so I believe it would be a little more efficient in large datasets, since we don't have to search the unique array each time we add an item.

var array =     [
  [
    {
      a: 'ggg'
    },
    {
      a: 'kkk'
    }
  ],
  [
    {
      a: undefined
    }
  ],
  [
    {
      a: 'ddd'
    }
  ],
  [
    {
      a: 'ggg'
    }
  ]
];
var map = {};
var uniq = [];

array.forEach(function(items){
    items.forEach(function(item){
        if(item.a) {
            map[item.a] = true;
        }
    });
});

for(var i in map){
    if(map.hasOwnProperty(i)){
        uniq.push(i);
    }
}

console.log(uniq);

answered Nov 3, 2016 at 13:23

twoLeftFeet

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Comments

Arnaud Rinquin · Accepted Answer · 2016-11-03 13:25:48Z

0

Providing you run babel or a recent version of nodejs, you don't need lodash or underscore for that.

The following example relies on a always being a string so it can be used as an object key.

var arr = [
  [{
    a: 'ggg'
  }, {
    a: 'kkk'
  }],
  [{
    a: undefined
  }],
  [{
    a: 'ddd'
  }],
  [{
    a: 'ggg'
  }]
];

var list = Object.keys(
  arr.reduce(function flatten(flattened, subarr) {
    return [...flattened, ...subarr]
  }, [])
  .filter(function hasA(obj) { return obj.a != null })
  .reduce(function putAintoAccumlator(accumulator, obj) {
    return {
      ...accumulator, [obj.a]: true
    }
  }, {})
)
console.log(list)

Another solution would be to use ES6 Set.

answered Nov 3, 2016 at 13:25

Arnaud Rinquin

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