Merge two arrays with alternating Values

Question

i would like to merge 2 arrays with a different length:

let array2 = [\"a\", \"b\", \"c\", \"d\"];
let array2 = [1, 2];

let outcome = [\"a\",1 ,\"b\", 2, \"         


        

Answer 1

A bit verbose solution that lets you choose which array goes first

const a = ['a', 'b', 'c'];
const b = [1, 4];
const combineAlternatingArrays = (a, b) => {
  let combined = [];
  const [shorter, larger] = [a, b].sort((a, b) => a.length -b.length);

  shorter.forEach((item, i) => {
    combined.push(larger[i], item);
  })
  combined.push(...larger.slice(shorter.length));

  return combined;
}
console.log(combineAlternatingArrays(a, b));

It is also possible to use a reduce, but the syntax is less clear in my opinnion.

const a = ['a', 'b', 'c'];
const b = [1, 4];
const combineAlternatingArrays = (a, b) => {
  const [shorter, larger] = [a, b].sort((a, b) => a.length -b.length);

  return shorter.reduce(
    (combined, next, i, shorter) => {
      return (i === (shorter.length -1)) ? [...combined, larger[i], next, ...larger.slice(shorter.length)] : [...combined, larger[i], next];
    },
    []
  );
}
console.log(combineAlternatingArrays(a, b));

Answer 2

Create an array of tuples. Each tuple contains 1 element from each array, flatten by spreading the array of tuples, and adding the leftover items from the arrays:

const a1 = ["a", "b", "c", "d"];
const a2 = [1,2];
const l = Math.min(a1.length, a2.length);

const merged = [].concat(...Array.from({ length: l }, (_, i) => [a1[i], a2[i]]), a1.slice(l), a2.slice(l));
  
console.log(merged);

Answer 3

Here's a modern solution that takes any number of arrays:

const braidArrays = (...arrays) => {
  const braided = [];
  for (let i = 0; i < Math.max(...arrays.map(a => a.length)); i++) {
    arrays.forEach((array) => {
      if (array[i] !== undefined) braided.push(array[i]);
    });
  }
  return braided;
};

Note that you could change Math.max to Math.min to only include up to the shortest array.

Here's a sample I/O:

braidArrays(['a','b','c','d'], [1,2,3], [99,98,97,96,95]);
// ['a', 1, 99, 'b', 2, 98, 'c', 3, 97, 'd', 96, 95]

Answer 4

You can do:

const array1 = ["a", "b", "c", "d"];
const array2 = [1, 2];
const mergeArrays = (a, b) => (a.length > b.length ? a : b)
  .reduce((acc, cur, i) => a[i] && b[i] ? [...acc, a[i], b[i]] : [...acc, cur], []);

console.log(mergeArrays(array1, array2)); // ["a",1 ,"b", 2, "c", "d"]

Answer 5

ONELINER: I assume that x=array1, y=array2, x and y can be arbitrary arr

[...x,...y].reduce((l,c,i)=>(i<x.length&&l.push(x[i]),i<y.length&&l.push(y[i]),l),[])

working example (for 3 cases)

Answer 6

This can be done rather simply using a splicing function within reduce:

function splicer(array, element, index) {
    array.splice(index * 2, 0, element);
    return array;
}

function weave(array1, array2) {
    return array1.reduce(splicer, array2.slice());
}

let array1 = ["a", "b", "c", "d"];
let array2 = [1, 2];

let outcome = weave(array1, array2);

console.log(outcome);