Syntax error Grouping array of array on the basis of elements in JavaScript

Grouping array of array on the basis of elements in JavaScript

Suppose, we have an array of arrays of numbers like this −

const arr = [[1, 45], [1, 34], [1, 49], [2, 34], [4, 78], [2, 67], [4, 65]];

Each subarray is bound to contain strictly two elements. We are required to write a function that constructs a new array where all second elements of the subarrays that have similar first value are grouped together.

So, for the array above, the output should look like −

const output = [
   [45, 34, 49],
   [34, 67],
   [78, 65]
];

We can make use of the Array.prototype.reduce() method that takes help of a Map() to construct the required array.

Therefore, let’s write the code for this function −

Example

The code for this will be −

const arr = [[1, 45], [1, 34], [1, 49], [2, 34], [4, 78], [2, 67], [4, 65]];
const constructSimilarArray = (arr = []) => {
   const creds = arr.reduce((acc, val) => {
      const { map, res } = acc;
      if(!map.has(val[0])){
         map.set(val[0], res.push([val[1]]) - 1);
      }else{
         res[map.get(val[0])].push(val[1]);
      };
      return { map, res };
   }, {
      map: new Map(),
      res: []
   });
   return creds.res;
};
console.log(constructSimilarArray(arr));

Output

The output in the console will be −

[ [ 45, 34, 49 ], [ 34, 67 ], [ 78, 65 ] ]
Updated on: 2020-10-20T12:15:43+05:30

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