Grouping array group into separate sub array group [duplicate]

Question

I have a JS array with strings, for example:

let a = ["a", "a", "a", "b", "c", "c", "b", "b", "b", "d", "d", "e", "e", "e"]

I need to compare for duplicate strings inside the array, and if a duplicate string exists it will be separated like this :

[ ["a", "a", "a"], ["b"], ["c", "c"], ["b", "b", "b"], ["d", "d"], ["e", "e", "e"] ]

I was trying to compare it with for loop, but I don't know how to write code so that array checks its own strings for duplicates, without an already pre-determined string to compare.

let a = ["a", "a", "a", "b", "c", "c", "b", "b", "b", "d", "d", "e", "e", "e"];

let b = [];

let len = a.length;

for (let i = 0; i < len; i++) {
  if (b.indexOf(a[i]) !== 1) {
    b.push(a[i]);
  }
}

console.log(b)

Jamiec · Accepted Answer · 2021-02-04 13:22:46Z

If you start with the zeroth element in the array you get [["a"]] and then if you iterate from the first element and just check whether its the same as the previous element you can determine whether to push to the existing last array, or start a new one.

So use slice to get the array except the zeroth element and forEach to accumulate your new array:

let a = ["a", "a", "a", "b", "c", "c", "b", "b", "b", "d", "d", "e", "e", "e"]

var result = [[a[0]]]
a.slice(1).forEach( (e,i) => {
  if(e == a[i]) {
    result[result.length-1].push(e);
  } else{
    result.push([e]);
  }
});
console.log(result)

If you wanted to keep track of a count also, thats fairly similar

let a = ["a", "a", "a", "b", "c", "c", "b", "b", "b", "d", "d", "e", "e", "e"]

var result = [{count:1, char:a[0]}]
a.slice(1).forEach( (e,i) => {
  if(e == a[i]) {
    result[result.length-1].count++;
  } else{
    result.push({count:1, char: e});
  }
});
console.log(result)

Mohammad Usman · Accepted Answer · 2021-02-04 11:24:11Z

1

You can use .reduce() method to get the desired output like below:

const data = ['a', 'a', 'a', 'b', 'c', 'c', 'b', 'b', 'b', 'd', 'd', 'e', 'e', 'e'];

const result = data.reduce(
  (r, c, i, a) => (
    c != a[i - 1] ? r.push([c]): r[r.length - 1].push(c), r
  ), []);

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Feb 4, 2021 at 11:24

answered Feb 4, 2021 at 11:10

Mohammad Usman

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1 Comment

Andreas Over a year ago

.map() and .fill() are unnecessary if you store the characters in the object instead of just a number...

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