takes a 2D matrix and iterates over it in isometric order (diagonal by diagonal)

isometric_matrix_iteration.js

const nbColumns = 5
const nbRows = 5

const matrix = new Array(nbColumns)
	.fill(null)
	.map(() => new Array(nbRows)
		.fill(null)
		.map(() => 0)
	)

drawMatrix(matrix)

let counter = 0
for(let i = 0; i < Math.max(nbColumns, nbRows) * 2 - 1; i++) {
	for (let j = Math.min(i, nbColumns - 1); j >= 0; j--) {
		if (j < nbColumns && i-j < nbRows)
			matrix[j][i-j] = counter++
	}
}

drawMatrix(matrix)

const isometric = drawIsometric(matrix)
drawMatrix(isometric)


function drawMatrix(matrix) {
	let output = '\n'
	for (const line of matrix) {
		if(!line) {
			output += '\n'
			continue
		}
		for (const cell of line) {
			if(cell === null)
				output += '   '
			else {
				if(cell < 10 && cell >= 0)
					output += '0'
				output += cell + ' '
			}
		}
		output += '\n'
	}
	console.log(output)
}

function drawIsometric(matrix) {
	const diagonalCount = Math.max(nbColumns, nbRows) * 2 - 1
	const result = new Array(diagonalCount)
		.fill(null)
		.map(() => new Array(diagonalCount)
			.fill(null)
		)

	for(let i = 0; i < Math.max(nbColumns, nbRows) * 2 - 1; i++) {
		for (let j = Math.min(i, nbColumns - 1); j >= 0; j--) {
			if (j < nbColumns && i-j < nbRows)
				result[i][Math.floor(diagonalCount / 2 - j + i / 2)] = matrix[j][i-j]
		}
	}
	return result
}