Join objects with one same property within different arrays

Question

I have this array, that contains more arrays with objects inside that contains information about words founded in pages. Here one example:

let data = [
  [],
  [{
      "word": "society",
      "count": 5,
      "pageIndex": 1
    },
    {
      "word": "identity",
      "count": 2,
      "pageIndex": 1
    }
  ],
  [{
      "word": "society",
      "count": 2,
      "pageIndex": 2
    },
    {
      "word": "identity",
      "count": 2,
      "pageIndex": 2
    }
  ],
  [{
      "word": "society",
      "count": 2,
      "pageIndex": 3
    },
    {
      "word": "identity",
      "count": 1,
      "pageIndex": 3
    }
  ],
  [],
  [],
  [{
    "word": "society",
    "count": 1,
    "pageIndex": 6
  }],
  [],
  [{
    "word": "society",
    "count": 1,
    "pageIndex": 8
  }],
  [{
    "word": "society",
    "count": 1,
    "pageIndex": 9
  }]
]

What I want is to build a final array of objects with this structure to join the information of each word founded in just one object

const final = [{
    "word": "society",
    "countFinal": 12,
    "pagesIndexes": [1, 2, 3, 6, 8, 9]
  },
  {
    "word": "identity",
    "countFinal": 5,
    "pagesIndexes": [1, 2, 3]
  }
]

Any ideas on how to achieve this in JS?

Rajneesh · Accepted Answer · 2020-09-20 07:33:11Z

3

You will first flat the data, afterward you can reduce (in order to group data based on word property). Once reduced, you can take Object.values of the object. Here is an implementation:

var data = [ [], [{ "word": "society", "count": 5, "pageIndex": 1 }, { "word": "identity", "count": 2, "pageIndex": 1 } ], [{ "word": "society", "count": 2, "pageIndex": 2 }, { "word": "identity", "count": 2, "pageIndex": 2 } ], [{ "word": "society", "count": 2, "pageIndex": 3 }, { "word": "identity", "count": 1, "pageIndex": 3 } ], [], [], [{ "word": "society", "count": 1, "pageIndex": 6 }], [], [{ "word": "society", "count": 1, "pageIndex": 8 }], [{ "word": "society", "count": 1, "pageIndex": 9 }]];

var result = Object.values(data.flat().reduce((a,{word, count, pageIndex})=>{
    a[word] = a[word] || {word, countFinal:0, pageIndexes:[]};
    a[word].countFinal+=count;
    a[word].pageIndexes.push(pageIndex);
    return a;
},{}));

console.log(result);

answered Sep 20, 2020 at 7:33

Rajneesh

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3 Comments

Rusty23 Over a year ago

wow, this is amazing. One question,is it possible to use flat already in node and in all browsers?

Rajneesh Over a year ago

@Rusty23 yes, if you can include support of es2016 inside your angular project then it is possible.

Rajneesh Over a year ago

@Rusty23 or if you have any third party library such as lodash or ramda then you have flatten or flat method to flat the array data.

Always Helping · Accepted Answer · 2020-09-20 07:37:07Z

var data = [
  [],
  [{
    "word": "society",
    "count": 5,
    "pageIndex": 1
  }, {
    "word": "identity",
    "count": 2,
    "pageIndex": 1
  }],
  [{
    "word": "society",
    "count": 2,
    "pageIndex": 2
  }, {
    "word": "identity",
    "count": 2,
    "pageIndex": 2
  }],
  [{
    "word": "society",
    "count": 2,
    "pageIndex": 3
  }, {
    "word": "identity",
    "count": 1,
    "pageIndex": 3
  }],
  [],
  [],
  [{
    "word": "society",
    "count": 1,
    "pageIndex": 6
  }],
  [],
  [{
    "word": "society",
    "count": 1,
    "pageIndex": 8
  }],
  [{
    "word": "society",
    "count": 1,
    "pageIndex": 9
  }]
];

let end_obj = {}
data.forEach(element => {
  element.forEach(sub => {
    if (!end_obj[sub.word]) {
      end_obj[sub.word] = {
        word: sub.word,
        countFinal: 0,
        pagesIndexes: []
      }
    }
    end_obj[sub.word].countFinal += sub.count
    end_obj[sub.word].pagesIndexes.push(sub.pageIndex)
  });
});

let end_arr = []
for (const key in end_obj) {
  const element = end_obj[key];
  end_arr.push(element)
}

console.log(end_arr);

Nick Parsons · Accepted Answer · 2020-09-20 07:48:04Z

One way could be to use a Map with .reduce(). The map would store keys which are the words from each object, along with its values being the modified objects with arrays for the pagesIndexes value. Whenever you come across a word that is already a key in the map, you can add to its pagesIndexes array. If you encounter a new word that isn't in the map, you can start a new array of its associated object which contains the current objects pageIndex. You can then grab the values from your Map using .values() and Array.from() to convert the value iterator into an array.

See example below

const data = [[], [{ "word": "society", "count": 5, "pageIndex": 1 }, { "word": "identity", "count": 2, "pageIndex": 1 } ], [{ "word": "society", "count": 2, "pageIndex": 2 }, { "word": "identity", "count": 2, "pageIndex": 2 } ], [{ "word": "society", "count": 2, "pageIndex": 3 }, { "word": "identity", "count": 1, "pageIndex": 3 } ], [], [], [{ "word": "society", "count": 1, "pageIndex": 6 }], [], [{ "word": "society", "count": 1, "pageIndex": 8}], [{ "word": "society", "count": 1, "pageIndex": 9 }] ];

const res = Array.from(data.reduce((acc, arr) => {
  return new Map([...acc, ...arr.map(c => {
    const o = acc.get(c.word);
    return [c.word, {...o, ...c, pagesIndexes: [...(o && o.pagesIndexes || []), c.pageIndex]}];
  })]);
}, new Map).values());

console.log(res);

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