CODEWITHSUNDEEP
javascriptimmutable.js
Ben Gannaway
Ben Gannaway

Reputation: 1083

immutable js flat zip two lists

If I have two immutable lists, 

const a = [1,2,3];
const b = [a,b,c,d];

is there an easy way to merge/zip them to result in:

const c = [1,a,2,b,3,c,d];

Upvotes: 1

Views: 680

Answers (3)

Kamesh
Kamesh

Reputation: 1152

If you want to develop a function from scratch then you can use the code below. Basically, the function merges the two array as interleaving the two. Consider 2 arrays, array1 = [1,2,3,4] and array2 = [a,b,c,d,e,f]. Then the below code will output a new array [1,a,2,b,3,c,4,d,e,f]

var i = 0;
var j = 0;
var k = 0;
var len1 = array1.length;
var len2 = array2.length;
var flag = true;

var newArr = [];

//Merge the 2 arrays till the smaller sized array

while (i < len1 && j < len2)
{
  if(flag){
   newArr[k] = array1[i];
   i++; k++;
   flag = false;
  }

else{
  newArr[k] = array2[j];
  j++; k++;
  flag = true;
 }
}

/* Copy the remaining elements of array1[], if there are any */

while (i < len1)
{
    newArr[k] = array1[i];
    i++;
    k++;
}

/* Copy the remaining elements of array2[], if there are any */

while (j < len2)
{
   newArr[k] = array2[j];
   j++;
   k++;
}

console.log(newArr)

Upvotes: 0

Harald Gliebe
Harald Gliebe

Reputation: 7564

Is interleave what you are looking for: https://facebook.github.io/immutable-js/docs/#/List/interleave

const a = List([1, 2, 3]);
const b = List([a, b, c, d]);
a.interleave(b)

Upvotes: 1

Andre Pena
Andre Pena

Reputation: 59396

const a = [1, 2, 3] don't make this array immutable at all. What const does is to guarantee that you're not reassigning a. Pushing or removing items to a don't constitute a reassignment.

This is a real immutable list using immutable.js:

const a = List([1, 2, 3]);

Now.. back to zip.

If you don't want another reference, you can just use a for in the smallest list and build the zip yourself. If you want a ready-made function, you might consider using Underscore's Zip, which does exactly what you want.

Upvotes: 0

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