Extract Unique Keys from an array of Objects

Question

I have an array of objects which looks like this:

[  
   {  
      "a":"alpha",
      "b":{  
         "x":true,
         "y":true
      }
   },
   {  
      "a":"beta",
      "b":{  
         "x":true,
         "z":true
      }
   }
]

I want to loop through this array to get a qnique list of all keys of 'b' alone. So, that my resulting array will be:

[x,y,z]

I tried the following:

const mykeys = myArray.map(item => Object.keys(item.b))

However, this only gves me: [[x,y], [y,z]]

How can I get the result as [x,y,z] instead.

Suren Srapyan · Accepted Answer · 2018-01-27 10:10:57Z

1

Use Array#reduce to concatenate the arrays into single array. Then using spread operator with Set you can get unique items.

Set lets you to store unique values.

const myArray = [  
   {  
      "a":"alpha",
      "b":{  
         "x":true,
         "y":true
      }
   },
   {  
      "a":"beta",
      "b":{  
         "x":true,
         "z":true
      }
   }
]

const mykeys = myArray.map(item => Object.keys(item.b))
                      .reduce((a,b) => a.concat(b));
                      
const uniqueKeys = [...new Set(mykeys)];

console.log(uniqueKeys);

answered Jan 27, 2018 at 10:10

Suren Srapyan

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1 Comment

asanas Over a year ago

This works great, thanks! I am asusming that this will work, no matter how many objects we have in the initial array. Can you confirm?

Nina Scholz · Accepted Answer · 2018-01-27 10:12:57Z

1

You could take a dynamic approach by using a variable for the wanted key of the object and get all inner keys.

This approach uses a default object if the given key does not exist.

var data = [{ a: "alpha", b: { x: true, y: true } }, { a: "beta", b: { x: true, z: true } }],
    key = 'b',
    unique = [
        ...new Set(
            data.reduce((r, o) => [...r, ...Object.keys(o[key]) || {}], [])
        )
    ];

console.log(unique);

answered Jan 27, 2018 at 10:12

Nina Scholz

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Comments

Ankit Agarwal · Accepted Answer · 2018-01-27 10:13:41Z

0

Here is the simple and much understanding way to achieve what you want.

var inputArray = [  
   {  
      "a":"alpha",
      "b":{  
         "x":true,
         "y":true
      }
   },
   {  
      "a":"beta",
      "b":{  
         "x":true,
         "z":true
      }
   }
];
var resArray = [];
inputArray.forEach((inputObj)=>{
  var keysForB = Object.keys(inputObj.b);
  keysForB.forEach((keyInB)=>{
    if(!resArray.includes(keyInB)){
       resArray.push(keyInB);
    }
  });
});

console.log(resArray);

answered Jan 27, 2018 at 10:13

Ankit Agarwal

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Comments

Hassan Imam · Accepted Answer · 2018-01-27 10:14:43Z

0

You can use Set with array spread syntax to get the unique keys.

const myArray = [{"a":"alpha","b":{"x":true,"y":true}},{"a":"beta","b":{"x":true,"z":true}}],
      myuniquekeys =[...new Set([].concat(...myArray.map(({b}) => Object.keys(b))))];
      
console.log(myuniquekeys);

edited Jan 27, 2018 at 10:14

answered Jan 27, 2018 at 10:09

Hassan Imam

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