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Grouping identical entries into subarrays - JavaScript
Let’s say, we have an array of numbers that have got identical entries. We are required to write a function that takes in the array and groups all the identical entries into one subarray and returns the new array thus formed.
For example: If the input array is −
const arr = [234, 65, 65, 2, 2, 234];
Then the output should be −
const output = [[234, 234], [65, 65], [2, 2]];
We will use a hashmap to keep a track of the elements already occurred and iterate over the array using a for loop.
Example
Following is the code −
const arr = [234, 65, 65, 2, 2, 234];
const groupArray = arr => {
const map = {};
const group = [];
for(let i = 0; i < arr.length; i++){
if(typeof map[arr[i]] === 'number'){
group[map[arr[i]]].push(arr[i]);
}else{
//the push method returns the new length of array
//and the index of newly pushed element is length-1
map[arr[i]] = group.push([arr[i]])-1;
}
};
return group;
}
console.log(groupArray(arr));Output
This will produce the following output in console −
[ [ 234, 234 ], [ 65, 65 ], [ 2, 2 ] ]
Updated on: 18-Sep-2020
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