move.js

var countOf = value => list => list.reduce((acc, num) => num === value ? acc + 1 : acc, 0);

var pipe = (...fns) => data => fns.reduce((value, fn) => fn(value), data);

var flatten = list => list.reduce((newList, item) => [].concat(newList, item), []);

var padStart = length => value => list => Array(length).fill(value).concat(list).slice(list.length);

var transpose = list => list[0].map((_, columnIndex) => list.map(row => row[columnIndex]));

var groupEveryFour = list => list.reduce((newList, _, index) => {
	return index % 4 === 0 ? [ ...newList, list.slice(index, index + 4) ] : newList;
}, []);

const removeZeros = list => list.filter(num => num !== 0);

var zerosToLeft = list => list.join('').replace(/0/g, '').padStart(4, '0').split('').map(Number);
var zerosToRight = list => list.join('').replace(/0/g, '').padEnd(4, '0').split('').map(Number);

var sumEquals = list => {
	const newList = [];
	for (let index = list.length - 1; index >= 0; index -= 1) {
		if (list[index] === list[index - 1]) {
			newList.push(list[index] * 2);
			index -= 1;
		} else {
			newList.push(list[index]);
		}
	}
	return newList.reverse();
};

/*
function sumEquals(list) {
	if (!Array.isArray(list) || list.length <= 0) return [];
	const tail = [ ...list ];
	const head = tail.shift();
	const nextHead = tail[0];
	// debugger;
	
	if (!nextHead) return [head]; 
	if (head === nextHead) {
		tail.shift();
		return [].concat(sumEquals(tail), head + nextHead );
	} else {
		return [].concat(sumEquals(tail), head);
	}
	
}
*/
var printWall = list => {
  return list.reduce((acc, item, index) => {
    return acc + (index % 4 === 0 ? '\n' : ' ') + item;
  }, '') + '\n';
};

var wall = [
  0,1,2,0,  
  3,0,0,4,  
  5,0,6,0,  
  0,7,0,8
];

var moveToTop = list => {
  return pipe(
    groupEveryFour,
    transpose,
    arr => arr.map(zerosToRight),
    transpose,
    flat,
  )(list);
};

var moveToBottom = list => {
  return pipe(
    groupEveryFour,
    transpose,
    arr => arr.map(zerosToLeft),
    transpose,
    flat,
  )(list);
};

var moveToRight = list => {
  return pipe(
    groupEveryFour,
    arr => arr.map(zerosToLeft),
    flat,
  )(list);
};

var moveToLeft = list => {
  return pipe(
    groupEveryFour,
    arr => arr.map(zerosToRight),
    flat,
  )(list);
};