[removed] Make an array of value pairs form an array of values

Question

Is there an elegant, functional way to turn this array:

[ 1, 5, 9, 21 ]

into this

[ [1, 5], [5, 9], [9, 21] ]

I kn

Answer 1

I noticed that the current solutions, in a way, all look ahead or behind (arr[i + 1] or arr[i - 1]).

It might be useful to also explore an approach that uses reduce and an additional array, defined within a function's closure, to store a to-be-completed partition.

Notes:

• Not a one liner, but hopefully easy to understand
• part doesn't have to be an array when working with only 2 items, but by using an array, we extend the method to work for n-sized sets of items
• If you're not a fan of shift, you can use a combination of slice and redefine part, but I think it's safe here.
• partitions with a length less than the required number of elements are not returned

const partition = partitionSize => arr => {
  const part = [];
  
  return arr.reduce((parts, x) => {
    part.push(x);
    
    if (part.length === partitionSize) {
      parts.push(part.slice());
      part.shift();
    }
    
    return parts;
  }, []);
};

const makePairs = partition(2);
const makeTrios = partition(3);

const pairs = makePairs([1,2,3,4,5,6]);
const trios = makeTrios([1,2,3,4,5,6]);


console.log("partition(2)", JSON.stringify(pairs));
console.log("partition(3)", JSON.stringify(trios));