I'm new to JavaScript, I'm trying to solve leetcode question 37. I need to a create a blank two dimensional array, I initially used the method in the comments; however, it doesn't work correctly, it will change all the value. Then, I used the for loop method to create array and currently it worked correctly. But I still cannot figured out why this will happen, could anyone explain the reason why this will happen, is this because of shallow copy?
var solveSudoku = function (board) {
// let rows = new Array(9).fill(new Array(10).fill(0)),
let rows = new Array(9);
for (let i = 0; i < 9; i++) {
rows[i] = new Array(10).fill(0);
}
let cols = new Array(9);
for (let i = 0; i < 9; i++) {
cols[i] = new Array(10).fill(0);
}
let boxes = new Array(9);
for (let i = 0; i < 9; i++) {
boxes[i] = new Array(10).fill(0);
}
// let cols = new Array(9).fill(new Array(10).fill(0)),
// boxes = new Array(9).fill(new Array(10).fill(0));
for (let i = 0; i < 9; i++) {
for (let j = 0; j < 9; j++) {
let c = board[i][j];
if (c !== '.') {
let n = parseInt(c),
bx = Math.floor(j / 3),
by = Math.floor(i / 3);
// 0代表为使用，1为使用过
rows[i][n] = 1;
console.log(i, n)
cols[j][n] = 1;
// box索引
boxes[by * 3 + bx][n] = 1;
}
}
}
fill(board, 0, 0)
function fill(board, x, y) {
// 完成填充条件
if (y === 9) return true;
// 下一个点的坐标
let nx = (x + 1) % 9,
// 判断进入是否下一行
ny = (nx === 0) ? y + 1 : y;
// 如果已经填充，则进入下一个点
if (board[y][x] !== '.') return fill(board, nx, ny);
// 没有被填充过
for (let i = 1; i <= 9; i++) {
let bx = Math.floor(x / 3),
by = Math.floor(y / 3),
box_key = by * 3 + bx;
if (!rows[y][i] && !cols[x][i] && !boxes[box_key][i]) {
rows[y][i] = 1;
cols[x][i] = 1;
boxes[box_key][i] = 1;
board[y][x] = i.toString();
console.log(board[y][x])
// 递归向下一个点求解
if (fill(board, nx, ny)) return true;
// 恢复初始状态
board[y][x] = '.';
boxes[box_key][i] = 0;
rows[y][i] = 0;
cols[x][i] = 0;
}
}
return false;
}
console.log(board);
};
The problem with fill(), at least with object, is that it passes the same object, by reference, to all element of the array. So if you mutate this object, then it will mutate every object of every arrays.
Note that in your case, you are creating a new Array object using it's constructor ( new Array() ) which makes them objects.
const matrix = new Array(5).fill(new Array(5).fill(0));
console.log(matrix);
In the previous snippet, you can see that the values of the other rows, from the second one to the end, are reference to the initial row.
To get around that, you can fill you array with empty values and then use the map() to create unique object for each position in the array.
const matrix = new Array(5).fill().map(function() { return new Array(5).fill(0); });
console.log(matrix);
As you can see in the previous snippet, all the rows are now their unique reference.
This is the reason all of your values were changed.
I've applied this solution to your code. I wasn't able to test it, because I wasn't sure of the initial parameters to pass.
I've also used anonymous function here ( function() { return; } ), but I would success using arrow function ( () => {} ) instead, if you are comfortable with them. It's cleaner.
var solveSudoku = function (board) {
let rows = new Array(9).fill().map(function() { return new Array(10).fill(0); }),
cols = new Array(9).fill().map(function() { return new Array(10).fill(0); }),
boxes = new Array(9).fill().map(function() { return new Array(10).fill(0); });
for (let i = 0; i < 9; i++) {
for (let j = 0; j < 9; j++) {
let c = board[i][j];
if (c !== '.') {
let n = parseInt(c),
bx = Math.floor(j / 3),
by = Math.floor(i / 3);
// 0代表为使用，1为使用过
rows[i][n] = 1;
console.log(i, n)
cols[j][n] = 1;
// box索引
boxes[by * 3 + bx][n] = 1;
}
}
}
fill(board, 0, 0)
function fill(board, x, y) {
// 完成填充条件
if (y === 9) return true;
// 下一个点的坐标
let nx = (x + 1) % 9,
// 判断进入是否下一行
ny = (nx === 0) ? y + 1 : y;
// 如果已经填充，则进入下一个点
if (board[y][x] !== '.') return fill(board, nx, ny);
// 没有被填充过
for (let i = 1; i <= 9; i++) {
let bx = Math.floor(x / 3),
by = Math.floor(y / 3),
box_key = by * 3 + bx;
if (!rows[y][i] && !cols[x][i] && !boxes[box_key][i]) {
rows[y][i] = 1;
cols[x][i] = 1;
boxes[box_key][i] = 1;
board[y][x] = i.toString();
console.log(board[y][x])
// 递归向下一个点求解
if (fill(board, nx, ny)) return true;
// 恢复初始状态
board[y][x] = '.';
boxes[box_key][i] = 0;
rows[y][i] = 0;
cols[x][i] = 0;
}
}
return false;
}
console.log(board);
};
Related
I create a buffer and then a Uint8Array on it, but the array does not have any values. I would expect it to have the values of the buffer. This is an easily reproducible example:
var buf = new ArrayBuffer(32);
for (var index = 0; index < 32; index++) buf[index] = index;
console.log(buf);
var arr = new Uint8Array(buf);
console.log(arr);
The thing I tried in reality is a date format converter like this:
//Buffers and views
function convertDateTimeToFormat(date, initialFormat, endFormat) {
var buf = new ArrayBuffer(14);
var result = new Uint8Array(buf);
console.log(date);
var initialPositions = {};
var endPositions = {};
var sizeSoFar = 0;
for (var c of initialFormat) {
if (c === 'y') {
initialPositions.y = new Uint32Array(date, sizeSoFar, 1);
} else {
initialPositions[c] = new Uint8Array(date, sizeSoFar, 2);
}
sizeSoFar += ((c === 'y') ? 4 : 2);
}
sizeSoFar = 0;
for (var c of endFormat) {
if (c === 'y') {
endPositions.y = new Uint32Array(buf, sizeSoFar, 1);
} else {
endPositions[c] = new Uint8Array(buf, sizeSoFar, 2);
}
sizeSoFar += ((c === 'y') ? 4 : 2);
}
for (var key in initialPositions) {
var limit = (key === 'y') ? 4 : 2;
for (var index = 0; index < limit; index++) endPositions[c][index] = initialPositions[c][index];
}
return result;
}
//2019-03-01 13:03:50
var buf = new ArrayBuffer( 14 );
buf[0] = 2;
buf[1] = 0;
buf[2] = 1;
buf[3] = 9;
buf[4] = 0;
buf[5] = 3;
buf[6] = 0;
buf[7] = 1;
buf[8] = 1;
buf[9] = 3;
buf[10] = 0;
buf[11] = 3
buf[12] = 5;
buf[13] = 0;
console.log(convertDateTimeToFormat(buf, "yMdHms", "yMdHms"));
console.log(convertDateTimeToFormat(buf, "yMdHms", "MdyHms"));
But due to the behavior I described at the start of this question, the results are all zeroes.
This works but it's not elegant, because it expects a date format and if I am to ensure that the input is agnostic to date formats, then the code will become very complicated:
//Buffers and views
var results = {};
var buf = new ArrayBuffer( 4 );
results.uint32 = new Uint32Array(buf);
results.int8 = new Uint8Array(buf);
results.uint8 = new Int8Array(buf);
results.int8[2] = -1;
console.log(results);
results.int8[2] = 0;
results.int8[1] = -1;
console.log(results);
results.int8[1] = 0;
results.int8[0] = -1;
console.log(results);
//Buffers and views
function convertDateTimeToFormat(date, format) {
var buf = new ArrayBuffer(14);
var result = new Uint8Array(buf);
var positions = {
y: 0,
M: 4,
d: 6,
H: 8,
m: 10,
s: 12
};
for (var index = 0; index < 14; index++) {
result[index] = date[positions[format[index]]++];
}
return result.join("");
}
var results = {};
//2019-03-01 13:03:50
var buf = new ArrayBuffer( 14 );
buf[0] = 2;
buf[1] = 0;
buf[2] = 1;
buf[3] = 9;
buf[4] = 0;
buf[5] = 3;
buf[6] = 0;
buf[7] = 1;
buf[8] = 1;
buf[9] = 3;
buf[10] = 0;
buf[11] = 3
buf[12] = 5;
buf[13] = 0;
console.log(convertDateTimeToFormat(buf, "yyyyMMddHHmmss"));
console.log(convertDateTimeToFormat(buf, "MMddyyyyHHmmss"));
An ArrayBuffer is just an object representing a slice of memory. It has a fixed size, that's it. It does not have properties that represent the contents, for that you'll need a typed array as a view on the buffer. Your code is just assigning properties to the buffer which works as it is an object, but it doesn't actually manipulate the byte contents which stay zero.
Don't explicitly instantiate the buffer at all if you don't need it. Just write
var arr = new Uint8Array(32);
for (var index = 0; index < 32; index++) arr[index] = index;
console.log(arr.buffer);
console.log(arr);
In your actual code, it seems you want to use an Uint8Array to store the numbers in individual bytes. And probably you should just pass that array instead of the underlying buffer into the function.
You can create it like this:
const arr = Uint8Array.of(2,0,1,9,0,3,0,1,1,3,0,3,5,0);
// or Uint8Array.from([2,0,1,9,0,3,0,1,1,3,0,3,5,0])
// or new Uint8Array(2,0,1,9,0,3,0,1,1,3,0,3,5,0]);
const buf = arr.buffer;
I've written a merge sort visualisation in p5.js which shows the steps of merge sort. This works fine as a sequential visualisation, but I'd quite like to show this as a true representation, where you can see each part of the array being sorted at the same time (with multiple sections being visualised sorting at the same time, to truly reflect the recursion). The code itself is relatively simple:
// Split the array recursively
let mid = Math.floor((right + left) / 2);
if (right - left < 1) {
return;
}
// My attempt to visualise this properly
await Promise.all([mergeSortSlice(array, left, mid), mergeSortSlice(array, mid + 1, right)]);
// THIS WORKS, but only for sequential sorting
// await mergeSortSlice(array, left, mid);
// await mergeSortSlice(array, mid + 1, right)
// Putting sleep(200) here also works, but doesn't show the steps of the sort as they are happening, just the result of each stage of the sort.
leftCounter = 0;
rightCounter = 0;
l = left;
r = mid + 1;
valuesStartIndex = l;
let leftArray = array.slice(left, r);
let rightArray = array.slice(r, right + 1);
while (rightCounter < rightArray.length && leftCounter < leftArray.length) {
if (leftArray[leftCounter] < rightArray[rightCounter]) {
array.splice(l + rightCounter, 1);
array.splice(valuesStartIndex, 0, leftArray[leftCounter]);
l++;
leftCounter++;
valuesStartIndex++;
await sleep(200);
} else {
array.splice(r, 1);
array.splice(valuesStartIndex, 0, rightArray[rightCounter]);
r++;
rightCounter++;
valuesStartIndex++;
await sleep(200);
}
}
The problem with using Promise.all is that the split parts of the array are getting mixed up, I believe due to the recursion? This is resulting in the array not getting sorted properly.
My timeout function:
async function sleep(ms) {
return new Promise(resolve => setTimeout(resolve, ms));
}
The setup function and draw loop:
let values = [50, 10, 80, 56, 30, 25, 15]
function setup() {
createCanvas(600, 190);
frameRate(60);
mergeSort(values)
}
function draw() {
rectWidth = 10;
background(23);
stroke(0);
fill(255);
for (let i = 0; i < values.length; i++) {
rect(i * rectWidth, height - values[i], rectWidth, values[i]);
}
}
The combination of async functions and recursion makes it difficult for me to come up with a solution for this. Any help/advice would be much appreciated.
You were actually very close to having a working solution. Your issue is that you are creating a bunch of global variables inside your mergeSortSlice function:
// These were all missing the let keyword
// And were therefore either assigning or implicitly declaring
// globally scoped variables.
let leftCounter = 0;
let rightCounter = 0;
let l = left;
let r = mid + 1;
let valuesStartIndex = l;
let leftArray = array.slice(left, r);
let rightArray = array.slice(r, right + 1);
When two instances of a function invocation being run as part of a Promise each of which await on timeouts, their execution is going to be interleaved (which you want so you can graphically represent the theoretical parallelism). However, when those functions alter global variables this is a classic shared memory multi-threading bug.
Here's an adaptation of your code with the bug fixed, highlighting added, and a slightly different delay strategy:
function merge_sort(p) {
const Mode = {
Shuffling: 0,
Sorting: 1
};
const spacing = 5;
let array = [...Array(40)].map((_, i) => i);
let highlights = [];
let itemWidth;
let itemHeight;
let currentMode = Mode.Shuffling;
let iterator;
let frameRate = 8;
let redrawPromise;
let signalRedraw;
p.setup = function() {
p.createCanvas(p.windowWidth, p.windowHeight);
p.frameRate(frameRate * 5);
itemWidth = (p.width - (spacing * (array.length + 1))) / array.length;
itemHeight = p.height - spacing * 2;
iterator = shuffle();
initRedrawPromise();
};
function initRedrawPromise() {
redrawPromise =
new Promise(resolve => {
signalRedraw = resolve;
});
redrawPromise.then(() => initRedrawPromise());
}
p.draw = function() {
p.background('white');
// draw
for (let i = 0; i < array.length; i++) {
if (highlights[i]) {
p.fill(highlights[i]);
} else {
p.fill('blue');
}
let fractionalHeight = (array[i] + 1) / array.length;
let pixelHeight = fractionalHeight * itemHeight;
p.rect(
(i + 1) * spacing + i * itemWidth,
spacing + (itemHeight - pixelHeight),
itemWidth,
pixelHeight
);
}
signalRedraw();
if (currentMode === Mode.Shuffling) {
// update
let next = iterator.next();
if (next.value) {
// Done suffle, switch to sort
currentMode = Mode.Sorting;
p.frameRate(frameRate);
sort().then(() => {
// switch back to shuffling
currentMode = Mode.Shuffling;
p.frameRate(frameRate * 5);
iterator = shuffle();
});
}
}
};
p.keyPressed = function(e) {
if (e.key === 'ArrowRight' || e.key === 'ArrowUp') {
frameRate++;
p.frameRate(frameRate);
} else if (e.key === 'ArrowLeft' || e.key === 'ArrowDown') {
frameRate = Math.max(0, frameRate - 1);
p.frameRate(frameRate);
}
}
// shuffle the array. yield false for each step where the array is not yet shuffled. yield true once the array is shuffled.
function* shuffle() {
// for each position in the array (except the last position),
// if the chosen item is not the current item, swap the two items.
for (let i = 0; i < array.length - 1; i++) {
highlight(i);
yield false;
let j = randomInt(i, array.length);
if (j !== i) {
highlight(i, j);
yield false;
swap(i, j);
highlight(j, i);
yield false;
} else {
highlight(i);
yield false;
}
}
yield true;
}
function sort() {
highlights = [];
return sortSlice(0, array.length - 1);
}
async function sortSlice(left, right) {
if (right - left < 1) {
return;
}
// Split the array recursively
let mid = Math.floor((right + left) / 2);
await Promise.all([sortSlice(left, mid), sortSlice(mid + 1, right)]);
for (let ix = left; ix <= right; ix++) {
highlights[ix] = undefined;
}
let leftCounter = 0;
let rightCounter = 0;
let l = left;
let r = mid + 1;
let valuesStartIndex = l;
let leftArray = array.slice(left, r);
let rightArray = array.slice(r, right + 1);
while (rightCounter < rightArray.length && leftCounter < leftArray.length) {
if (leftArray[leftCounter] < rightArray[rightCounter]) {
array.splice(l + rightCounter, 1);
array.splice(valuesStartIndex, 0, leftArray[leftCounter]);
highlights[valuesStartIndex] = 'green';
highlights[r] = 'red';
l++;
leftCounter++;
valuesStartIndex++;
} else {
array.splice(r, 1);
array.splice(valuesStartIndex, 0, rightArray[rightCounter]);
highlights[valuesStartIndex] = 'green';
r++;
rightCounter++;
valuesStartIndex++;
highlights[l + rightCounter] = 'red';
}
// at each merge step wait for a redraw that shows this step
await redrawPromise;
highlights[valuesStartIndex - 1] = 'gray';
for (let ix = valuesStartIndex; ix <= right; ix++) {
highlights[ix] = undefined;
}
}
}
function swap(i, j) {
const tmp = array[i];
array[i] = array[j];
array[j] = tmp;
}
function randomInt(lowerBound, upperBound) {
return lowerBound + Math.floor(Math.random() * (upperBound - lowerBound));
}
function highlight(i, j) {
highlights = [];
if (i !== undefined) {
highlights[i] = 'green';
}
if (j !== undefined) {
highlights[j] = 'red';
}
}
}
sketch = new p5(merge_sort);
<script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.4.0/p5.js"></script>
My code currently has a bug where my 2-d array with the bool value false suddenly contains true values before it is assigned any. My current guesses is either console.log somehow is delayed and picks up the values after it is called, with the updated values or that there is some issue that I don't understand about how scope works in javascript.
As seen below console.log(visited[i][j]) results in false for all values but the
new visited line contains true values even before the following is called.
const field_size = 800;
const cells_in_row = 5;
const frames_per_second = 1;
const cell_size = field_size / cells_in_row;
class Cell {
constructor(x,y) {
this.value = 0;
this.x = x;
this.y = y;
this.coordinates = [x*cell_size,y*cell_size];
}
fill() {
this.value = 1;
}
clear() {
this.value = 0;
}
}
const get_new_grid = (random = 0) => {
const grid = new Array(cells_in_row);
for (let i = 0; i < grid.length; i++) {
grid[i] = new Array(cells_in_row);
for (let j = 0; j < grid.length; j++) {
grid[i][j] = new Cell(i,j);
v = 0;
if (random) {
v = Math.floor(Math.random() * 2);
}
grid[i][j].value = v;
}
}
return grid;
}
const get_islands = (grid) => {
// bool array to mark visited cells
let visited = new Array(cells_in_row);
for (let i = 0; i < grid.length; i++) {
visited[i] = new Array(cells_in_row);
for (let j = 0; j < grid[0].length; j++) {
visited[i][j] = false;
}
}
console.log("New Visited", visited);
let count = 0;
let islands = [];
let island_coords = [];
for (let i = 0; i < grid.length; i++) {
for (let j = 0; j < grid.length; j++) {
if (visited[i][j] == false && grid[i][j].value == 1) {
// visit all cells in this island and increment island count
// dfs will return array of coordinates of island
[visited, island_coords] = dfs(i, j, grid, visited, island_coords);
console.log(visited);
islands.push(island_coords);
count += 1;
}
}
}
return [count, islands];
}
const dfs = (i, j, grid, visited, island_coords) => {
let row_nbr = [-1, -1, -1, 0, 0, 1, 1, 1];
let col_nbr = [-1, 0, 1, -1, 1, -1, 0, 1];
visited[i][j] = true;
island_coords.push([i,j]);
for (let k = 0; k < 8; k++) {
if (is_safe(i + row_nbr[k], j + col_nbr[k], grid, visited)) {
console.log("DFSing " + i + "," + j);
[visited, island_coords] = dfs(i + row_nbr[k], j + col_nbr[k],
grid, visited, island_coords);
}
}
return [visited, island_coords];
}
const is_safe = (i, j, grid, visited) => {
return (i >= 0 && i < grid.length &&
j >= 0 && j < grid.length &&
!(visited[i][j]) && grid[i][j].value === 1);
}
(function () {
var old = console.log;
var logger = document.getElementById('log');
console.log = function () {
for (var i = 0; i < arguments.length; i++) {
if (typeof arguments[i] == 'object') {
logger.innerHTML += (JSON && JSON.stringify ? JSON.stringify(arguments[i], undefined, 2) : arguments[i]) + '<br />';
} else {
logger.innerHTML += arguments[i] + '<br />';
}
}
}
})();
window.onload = () => {
const canvas = document.getElementById('canvas');
const grid = get_new_grid(random = 0);
grid[0][0].value = true;
grid[0][1].value = true;
grid[1][0].value = true;
grid[1][1].value = true;
const islands = get_islands(grid);
console.log(grid);
console.log(islands);
}
<!DOCTYPE html>
<html>
<body>
<script src="gameoflife.js"></script>
<pre id="log"></pre>
</body>
</html>
EDIT:
So I updated the snippet but it looks like it works on this end, however it shows the behavior I mentioned before on my own browser even with the exact same javascript code and html in the snippet.
Mentioned in the comments by Niet, objects logged to the console are live.
I get convergence, nevertheless, the results are never the same when the algorithm is refreshed. This occurs even when the data observations is the same dataset. Can anyone tell me where my methodology is wrong? For the life of me I can't figure out where the process is wrong.
function kmeans2(k, data, canvas, converge) {
this.canvas = jsHS.GetDimensions(canvas);
this.k = k;
this.centroids = []; // Array of centroids
this.centroids2compare = [];
this.data = data;
this.converge = converge;
this.init();
}
kmeans2.prototype.distance = function () {
var dif = 0,
iArray = jsHS.isArray(arguments);
if (iArray) {
if (arguments.length > 2) {
for (var i = 0; i < arguments.length; i+2) {
var p0 = arguments[i],
p1 = arguments[i + 1];
dif += Math.pow(p0[0] - p1[0], 2);
dif += Math.pow(p0[1] - p1[1], 2);
}
}
else {
var pd0 = arguments[0],
pd1 = arguments[1];
dif += Math.pow(pd0[0] - pd1[0], 2);
dif += Math.pow(pd0[1] - pd1[1], 2);
}
}
return Math.sqrt(dif);
};
kmeans2.prototype.Means = function (Array) {
var bin = 0;
[].forEach.call(Array, function(a){
bin += a;
});
return bin / Array.length;
};
kmeans2.prototype.init = function () {
for (var l = 0; l < this.k; l++) {
var dataItem = this.data[Math.floor(Math.random() * this.data.length)];
this.centroids.push(dataItem);
}
for (var i = 0; i < this.centroids.length; i++) {
if (i > 0) {
var distance = this.distance(this.centroids[i], this.centroids[i - 1]);
console.log(distance);
}
}
this.clusterCentroids(); // return centroid center after calculating means.
};
kmeans2.prototype.clusterCentroids = function () {
var points0 = [];
this.centroids2compare = this.centroids;
// Find distances between centroid and observations.
for (var d = 0; d < this.data.length; d++) {
var cinbin = [];
for (var c0 = 0; c0 < this.k; c0++) {
var dis = this.distance(this.centroids[c0], this.data[d]);
cinbin.push({ 'cid': c0, 'distance': dis });
}
var minResult = cinbin.reduce((cid, obj) => {
return obj.distance < cid.distance ? obj : cid;
});
points0.push({ 'id': d, 'datapoint': this.data[d], 'centroid': minResult.cid });
}
// Assign observations their appropriate centroid.
var centroidBin = [];
for (var c = 0; c < this.k; c++) {
var cb = [];
for (var p = 0; p < points0.length; p++) {
if (c === points0[p].centroid) {
cb.push(points0[p]);
}
}
centroidBin.push(cb);
}
// Calculate the mean distance between centroids and its assigned observations.
this.centroids = [];
for (var bin = 0; bin < centroidBin.length; bin++) {
var xAxis = [],
yAxis = [],
cb0 = centroidBin[bin];
[].forEach.call(cb0, function (dp) {
xAxis.push(dp.datapoint[0]);
yAxis.push(dp.datapoint[1]);
});
var xMean = this.Means(xAxis);
var yMean = this.Means(yAxis);
this.centroids.push([xMean, yMean]);
}
// Test for convergence. If stored centroids equal new centroids then convergence is achieved.
if (JSON.stringify(this.centroids2compare) !== JSON.stringify(this.centroids)) {
this.centroids2compare = [];
points0 = [];
this.clusterCentroids();
}
else {
this.converge(centroidBin, this.centroids);
}
};
window['jsHS']['kmeans2'] = kmeans2;
Implementation
var k50 = new jsi.kmeans2(5, Array50, canvas, function (con, centroids) {
var count50 = 0;
var cmark = {
x: 0,
y: 0,
rad:0,
clr: null,
setArc: function () {
ctx.beginPath();
ctx.arc(this.x, this.y, this.rad, 0, Math.PI * 2, true);
ctx.fillStyle = this.clr;
ctx.fill();
}
};
[].forEach.call(centroids, (c) => {
cmark.x = c[0];
cmark.y = c[1];
cmark.clr = '#0B6623';
cmark.rad = 25;
cmark.setArc();
});
});
This example plots the centroids on a canvas area fine enough but when the browser refreshes the centroids change.
I haven't looked much at your code, but I know that the k-means algorithm tends to give different results when you run it several times. This is because it's highly dependent on where the first centroids (which are selected randomly) are located.
The algorithm can find a local minimum and get "stuck" there, and terminate.
There's no guarantee that you will find the global minimum the first time you run it.
I want to generate a vector of 100 values composed by [1 0]:
This is how I did it in Matlab:
n = 100;
Seq1 = [1 0]; % sequence of 1-0
Vector = repmat(Seq1,(n/2),1); % Creates n/2 sequences of 1-0
The result is a vector like: [1 0 1 0 1 0 1 0...]
Is there a way to get the same result with JavaScript?
You could mimic the function repmat with a while loop.
function repmat(array, count) {
var result = [];
while (count--) {
result = result.concat(array);
}
return result;
}
var nTrials = 100,
Seq1 = [1, 0],
Vector = repmat(Seq1, nTrials / 2);
console.log(Vector);
Assuming you're looking for a way to add a 1 and then a 0, not an array containing 1 and 0:
var myArray = [];
nTrials = 30;
for(i = 1; i<= nTrials/2; i++){
myArray.push(1);
myArray.push(0)
}
document.body.innerHTML = myArray[1];}
https://jsfiddle.net/6seqs6af/1/
FWIW, here is the full repmat implementation in JavaScript.
It uses arrow functions (=>) which isn't available in all browsers.
// Seq1 is an Array (1D vector). We need a Matrix which JavaScript doesn't have
// natively. But we can derive a Matrix type from an Array by adding
// `numberOfRows` and `numberOfColumns` properties as well as a `set` method
function Matrix(numberOfRows, numberOfColumns) {
this.numberOfColumns = numberOfColumns;
this.numberOfRows = numberOfRows;
this.length = numberOfColumns * numberOfRows;
this.fill();
}
Matrix.prototype = Array.prototype;
Matrix.prototype.set = function() {
for (var i = 0; i < arguments.length; i++) {
this[i] = arguments[i];
}
return this;
}
Matrix.prototype.toString = function() {
return this.reduce((acc, x, idx) => acc + (idx % this.numberOfColumns === this.numberOfColumns - 1 ? x + '\n' : x + ', '), '');
}
Matrix.prototype.at = function(row, column) {
return this[row * this.numberOfColumns + column];
}
// Repmap
// ======
function repmat(mat, repeatColumns, repeatRows) {
var numberOfColumns = mat.numberOfColumns * repeatColumns;
var numberOfRows = mat.numberOfRows * repeatRows;
var values = [];
for (var y = 0; y < numberOfRows; y++) {
for (var x = 0; x < numberOfColumns; x++) {
values.push(mat.at(y % mat.numberOfRows, x % mat.numberOfColumns));
}
}
var result = new Matrix(numberOfRows, numberOfColumns);
result.set.apply(result, values);
return result;
}
// Calculation
// ===========
var nTrials = 100;
var seq1 = new Matrix(1, 2);
seq1.set(1, 0);
var vector = repmat(seq1, nTrials / 2, 1);
console.log(vector.toString());