If the final chunk of a chunked array can't be split evenly then add empty strings into the fin-CodePudding

I have this problem where I want to split an array of elements into equal chunks of three. But if the final chunk can't be split evenly then add empty strings.

I am using lodash _.chunk method but not sure how to add extra empty strings in the final chunk.

// I will get unknown number elements in the array.

const arr1 = [{elem1}, {elem2}, {elem3}, {elem4}]
// above array does have 4 elements. If I use _.chunk I will get something like [[{elem1},{elem2},{elem3}], [{elem4}]]
// I am looking to get something like [[{}, {}, {}], [{}, '', '']].

Can somebody please let me know how to achieve this in JS?

CodePudding user response：

First, you will need to increase the array length until it get a divisible length by 3 after that you could slice the array simply using slice method like this

let arr = [{foo: 'bar'}, {foo: 'bar'}, {foo: 'bar'}, {foo: 'bar'}];

function split(arr){
   let res = [];
   
   while(arr.length % 3 != 0){
      arr.push({foo: 'bar'});      
   }
       
   for(let i = 0; i < 3; i  )
    res.push(arr.slice(i * 2, i * 2   (arr.length / 3)))
   
   return res;
}

console.log(split(arr));

CodePudding user response：

Use Array.prototype.concat() to adjust array size to multiple of 3 and Array.prototype.reduceRight() to split into chunks:

const src = [{el: '1'}, {el: '2'}, {el: '3'}, {el: '4'}, {el: '5'}, {el: '6'}, {el: '7'}]

const chunkOfThree = arr => 
  arr
    .concat(
      arr.length%3
        ? Array(3-arr.length%3).fill('')
        : []
    )
    .reduceRight((r,_,__,s) => 
      (r.push(s.splice(0,3)),r),[])
      
console.log(chunkOfThree(src))

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CodePudding user response：

I'm not sure why everyone is rewriting chunk. Do the chunking with lodash's _.chunk like you are, then just fill in the last chunk.

let chunkedArray = [
  [{foo:'bar'},{foo:'bar'},{foo:'bar'}],
  [{foo:'bar'},{foo:'bar'},{foo:'bar'}],
  [{foo:'bar'}],
];
const chunkSize = 3;
const filler = '';
// fill in
// Create a new array, 
chunkedArray = [
  // with all of the chunks except the last one
  ...chunkedArray.slice(0,-1), 
  // Add the last chunk
  [
    // with all of its contents
    ...chunkedArray[chunkedArray.length - 1], 
    // plus the contents of a new array, the length of a chunk minus the length
    // of the last chunk, filled with an empty string (or whatever)
    ...new Array(chunkSize - chunkedArray[chunkedArray.length - 1].length).fill(filler)
  ]
];
// now chunkedArray is complete, all arrays the same size
console.log(chunkedArray);

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