I want to create an array matrix like this:
createMatrix(4);
// logs:
[[0,0,0,0],
[0,0,0,0],
[0,0,0,0],
[0,0,0,0]];
Currently my solution is :
function createMatrix (n) {
var innerArr;
var outerArr = [];
for (var i=0; i<n; i++){
innerArr = [];
for (var j=0; j<n; j++) {
innerArr.push(0);
}
outerArr.push(innerArr);
}
}
console.log(outerArr);
Is there a more efficient way to do this? This will iterate nxn times which is very inefficient for something very simple.
With the ECMAScript 2015 function Array.prototype.fill():
Array(row_count).fill(Array(column_count).fill(0)).map(a => a.slice())
Explanation:
// a sparse array with row_count "absent" items:
Array(row_count)
// an array with column_count members with the value 0:
Array(column_count).fill(0)
// an array with row_count times the identic array as value:
Array(row_count).fill(Array(column_count).fill(0))
// shallow copy the inner array:
Array(row_count).fill(Array(column_count).fill(0)).map(a => a.slice())
Speed?
n=4: http://jsperf.com/creatematrix/1
n=8: http://jsperf.com/creatematrix/2
n=16: http://jsperf.com/creatematrix/3
n=32: http://jsperf.com/creatematrix/4
Seemingly the Array.prototype.fill() variant gets faster as the matrix grows (in relation to the loops). At least in Firefox. YMMV.
There are a couple of approaches you could take:
concat()/slice()
var numCols = 4;
var numRows = 4;
var innerArrSrc = [];
var outerArr = [];
for (var i = 0; i < numCols; i++) {
innerArrSrc.push(0);
}
for (var j = 0; j < numRows; j++) {
outerArr.push(innerArrSrc.concat()); // Could also use innerArrSrc.slice();
}
Both Array.prototype.concat() and Array.prototype.slice() will return a shallow copy of the source array.
one-dimensional array
Alternatively, you could represent your matrix as an one-dimensional array rather than a multi-dimensional one and provide functions to access specific indexes based on row-column values:
var numRows = 4;
var numCols = 4;
var len = numRows * numCols;
var outerArr = [];
for (var i = 0; i < len; i++) {
outerArr.push(0);
}
A function to access a specific index of a matrix represented this way might look like:
function getMatrixIndex(myMatrix, col, row, numCols) {
var index = row * numCols + col;
return myMatrix[index];
}
Array.prototype.fill
If you want to take advantage of new ES6 features Array.prototype.fill should suit your needs:
// Multi-dimensional
var numRows = 4;
var numCols = 4;
var outerArr = new Array(row_count).fill(new Array(column_count).fill(0)).map(a => a.slice());
// Or one-dimensional
var len = numRows * numCols;
var oneDim = new Array(row_count * column_count).fill(0);
jsPerf tests
You can run this jsPerf test to see which is fastest. I've tested in:
Firefox 42.0 32-bit on Windows NT 10.0 64-bit
Chrome 44.0.2403.130 32-bit on Windows NT 10.0 64-bit
Chrome 47.0.2526.73 32-bit on Windows NT 10.0 64-bit
Android Browser 42.0 (Gecko) on Android 6.0
Related
I tried to use Typed arrays instead of arrays, to reduce memory:
function createarrayInt8(numrows,numcols,number){
var arr = new Int8Array(numrows);
for (var i = 0; i < numrows; ++i){
var columns = new Int8Array(numcols);
for (var j = 0; j < numcols; ++j){
columns[j] = number;
}
arr[i] = columns;
}
return arr;
}
But i can't create multidimensional Typed array.
Why?
Do i have to cast only the "number" var to Int8?
A typed Int8Array can only hold 8-bit integers. So arr[i] = columns won't work since columns is of type Int8Array which cannot be converted to and stored (in any meaningful way) as a an 8-bit integer.
Solution: Either make arr a generic Array whose elements can be arrays or - probably the more advanced but usually more performant solution - store your multidimensional array as a single flat array of size numrows * numcols and access an element via arr[column + row * numcols]:
var numrows = 5, numcols = 4;
var arr = new Int8Array(numrows * numcols).fill(0);
arr[3 + 1 * numrows] = 1; // col = 3, row = 1
console.log (arr);
How to generate an array with function like this?
var name = ["monkey","monkey"..."horse","horse",..."dog","dog",..."cat","cat"...]
In my real case, I may have to repeat each name 100 times..
Assuming that you already have that words in a array try this code:
var words = ["monkey", "hourse", "dog", "cat"];
var repeatWords = [];
for(var i = 0; i < words.length; i++)
{
for(var j = 0; j < 100; j++)
{
repeatWords.push(words[i]);
}
}
You can try this, specifying the words to be used, and the times to create the array you need.
var neededWords = ["Cat", "Hourse", "Dog"];
var finalArray = [];
var times = 10;
for (var i = 0; i < neededWords.length; i++) {
for (var n = 0; n < times; n++) {
finalArray.push(neededWords[i]);
}
}
console.log(finalArray);
Hope that helps!
If I understood correctly you need a function that takes as an argument a collection of items and returns a collection of those items repeated. From your problem statement, I assumed that the repetition has to be adjusted by you per collection item - correct me if I am wrong.
The function I wrote does just that; it takes an object literal {name1:frequency1,name2:frequency2..} which then iterates over the keys and pushes each one as many times as indicated by the associated frequency in the frequencyMap object.
function getRepeatedNames( frequencyMap ) {
var namesCollection = [];
Object.keys(frequencyMap).forEach(function(name,i,names){
var freq = frequencyMap[name];
freq = (isFinite(freq)) ? Math.abs(Math.floor(freq)) : 1;
for (var nameCounter=0; nameCounter<freq; nameCounter++) {
namesCollection.push(name);
}
});
return namesCollection;
}
Non-numeric values in the frequency map are ignored and replaced with 1.
Usage example: If we want to create an array with 5 cats and 3 dogs we need to invoke
getRepeatedNames({cat: 2, dog: 3}); // ["cat","cat","dog","dog","dog"]
I'm working on Google Script and I'm testing different ways to create two dimensions arrays.
I have created an array like this:
var codes = new Array(6);
for (var i = 0; i < 6; i++) {
codes[i] = new Array(4);
}
codes[0][0]="x";
codes[0][1]="x";
codes[0][2]="x";
codes[0][3]="x";
codes[1][0]="x";
codes[1][1]="x";
codes[1][2]="x";
codes[1][3]="x";
codes[2][0]="x";
codes[2][1]="x";
codes[2][2]="x";
codes[2][3]="x";
codes[3][0]="x";
codes[3][1]="x";
codes[3][2]="x";
codes[3][3]="x";
codes[4][0]="x";
codes[4][1]="x";
codes[4][2]="x";
codes[4][3]="x";
codes[5][0]="x";
codes[5][1]="x";
codes[5][2]="x";
codes[5][3]="x";
And it is working fine.
I read following links here, here and here.
But when I do it like this:
var codes = new Array(6);
for (var i = 0; i < 6; i++) {
codes[i] = new Array(4);
}
codes[0]=["x","x","x","x"];
codes[1]=["x","x","x","x"];
codes[2]=["x","x","x","x"];
codes[3]=["x","x","x","x"];
codes[4]=["x","x","x","x"];
codes[5]=["x","x","x","x"];
It didn't work, so I tried like this:
var codes = new Array([["x","x","x","x"],["x","x","x","x"],["x","x","x","x"],["x","x","x","x"],["x","x","x","x"],["x","x","x","x"]]);
it didn't work either.
When the code don't work, I get no error, just no display of the values.
What am I doing wrong? It looks to be the same code and the two not working ways are recommended in many documentations.
W3schools says that there is no need to use new Array().
For simplicity, readability and execution speed, use literal method ex:
var animals = ["cat", "rabbit"];
Reason why your code was not working is that you're equaling codes inside the loop and after end of loop scope 'codes' is getting only the last set array. Instead you should push those arrays to codes.
var codes = [];
for (var i = 0; i < 6; i++) {
codes.push([i]);
}
console.log(codes)
codes[0]=["x","x","x","x"];
codes[1]=["x","x","x","x"];
codes[2]=["x","x","x","x"];
codes[3]=["x","x","x","x"];
codes[4]=["x","x","x","x"];
codes[5]=["x","x","x","x"];
Better yet, two for loops to create the double array:
var codes = [], // Initiate as array, in Javascript this is actually fastre than using new (I don't know any cases you should use new)
rows = 6,
columns = 6;
for (var i = 0; i < rows; i++){
codes.push([]); // Initiate
for (var j = 0; j < columns; j++){
codes[i][j] = 'x';
}
}
Other idea, pre-initiate an array with the correct columns then copy:
var arrTemp = [],
codes = [],
rows = 6,
columns = 6;
for (var j = 0; j < columns; j++)
arrTemp[i] = 'x';
for (var i = 0; i < rows; i++)
codes.push( arrTemp.slice(0) ); // If you just push the array without slice it will make a reference to it, not copy
Other way to pre-initiate the array with 'x's:
arrTemp = Array.apply(null, Array(columns)).map(function () {return 'x'});
My goal is to make a randomly generated 2D Array in Javascript, that has an X amount of the same one character value while the rest of the values are equal to another character.
In this example, there are 10 rows and 10 columns for the 2D Array. 20 out of the possible 100 values of the Array should be equal to 'Y' (for yes) and the 80 others should be 'N' (for no). I want the 'Y's to be randomly placed all over the Array, and I absolute need exactly 20 of them to be 'Y's and the rest 'N's.
I had a less efficient way before, and I thought to try this approach, where after I define the Array, I make the first X amount of values a 'Y' and then the rest all 'N's. Then I shuffle the array, (using the shuffle from the underscore library) so that the 'Y's are all spread out randomly everywhere.
Is this an efficient way of getting what I need done? Are there any better solutions? I tried making a JSFiddle with my example, but the site appears to be down at the moment.
(I was unable to test my code yet to see if the shuffle worked correctly on my 2D array)
var rows = 10;
var cols = 10;
var elements = 20;
//Define Empty Array
var test = new Array(rows);
for (var k = 0; k < rows; k++)
{
test[k] = Array(cols);
}
var i = 1;
for (var x = 0; x < rows; x++)
{
for (var y = 0; y < cols; y++)
{
if (i <= elements)
{
test[x][y] = "Y";
}
else
{
test[x][y] = "N";
}
}
}
//Shuffle all those values so they're no longer in order
var shuffledTest = _.shuffle(test);
//Print in rows
for (var x = 0; x < rows; x++)
{
console.log(shuffledTest[x]);
}
A very simple solution is to first create an array, fill it with a number of "N"s, insert the "Y"s at random indexes, and then finally splitting it into the 2-dimensional array that you want:
var tmpArr = [], // Temporary 1-dimensional array to hold all values
arr = [], // The final 2-dimensional array
rows = 10,
cols = 10,
elements = 20; // Number of "Y"s
// 1. Fill temporary array with "N"s
for (var i = 0; i < rows * cols - elements; i += 1) {
tmpArr.push("N");
}
// 2. Insert "Y"s at random indexes in the temporary array
for (var i = 0; i < elements; i += 1) {
var index = Math.round(Math.random() * (tmpArr.length + 1));
tmpArr.splice(index, 0, "Y");
}
// 3. Split temporary array into 10 seperate arrays
// and insert them into the final array
for (var i = 0; i < rows; i += 1) {
var row = tmpArr.slice(i * cols, (i + 1) * cols);
arr.push(row);
}
JSBin to illustrate: http://jsbin.com/luyacora/1/edit
You can try this solution, it uses underscores range to create a pair of arrays to use as iterators, though their values don't matter.
Play around with the randomizer function to get an even distribution of 'y's
JSBIN: http://jsbin.com/yaletape/1/
var rows = _.range(0, 10, 0);
var columns = _.range(0, 10, 0);
function randomizer(mult){
return Math.floor((Math.random()*mult)+1);
}
var y_count = 0;
var matrix = _.map(rows, function(){
return _.map(columns, function(v, i){
var value;
var y_allowed = randomizer(3);
var current_y_count = 0;
if(y_count < 20 && current_y_count < y_allowed){
var rand = randomizer(5);
if(rand > 4){
value = 'y';
current_y_count++;
y_count++;
}
}
if(!value){
value = 'n';
}
return value;
});
});
//The above could be simplified to
var matrix = _.range(0,10,0).map(function(){
return _.range(0,10,0).map(function(){
//put the logic code from above here
});
});
Maybe shuflle a 2D array is not the best way. As #Zeb mentioned, here is some code that fill random positions with the 'Y' value. After that, the other positions are filled with 'N'.
http://plnkr.co/edit/avyKfgsgOSdAkRa1WOsk
var arr = [];
var cols = 10;
var rows = 10;
var positions = rows*cols; // 100
var YQty = 10; // only 10 'Y' are needed
// 'Y' values.
for(i = 0; i < YQty; i++)
{
do
{
x = parseInt(Math.random() * cols);
y = parseInt(Math.random() * rows);
filled = false;
if (typeof(arr[x]) == "undefined")
{
arr[x] = [];
}
if (typeof(arr[x][y]) == "undefined")
{
arr[x][y] = 'Y';
filled = true;
}
}
while (!filled);
}
// 'N' values.
for (x = 0; x < cols; x++)
{
if (typeof(arr[x]) == "undefined")
{
arr[x] = [];
}
for (y = 0; y < rows; y++)
{
if (arr[x][y] != 'Y')
{
arr[x][y] = 'N';
}
}
}
Shuffling the multidimensional array is not the best approach. Seeing as any sort is worse than linear time complexity. The easiest solution would be to create your multidimensional array and then set each index value to the char you want the 'rest' of the values to be. Then for 1 -> the number of other char value choose a random index and set that to the char.
Note: If the randomly picked spot has already been changed you need to choose a new one to make sure you have the right amount at the end.
I am trying to convert Java code to Javascript and I am trying to assign data to 3 dimensional array and I am getting "TypeError: can't convert undefined to object " error. Following is my code. Thanks in advance for any help.
var initData = [[2], [12], [2]];
for (var i = 0; i < 12; i++)
{
initData[0][i][0] = -1;
initData[0][i][1] = -1;
initData[1][i][0] = -1;
initData[1][i][1] = -1;
}
[[2], [12], [2]];
That's not a declaration of dimensions, that's four array literals. There are no multidimensional arrays in JS. They're just one-dimensional lists that can contain arbitrary values (including other lists).
To create and fill an array that contains other arrays you have to use the following:
var initData = []; // an empty array
for (var i = 0; i < 2; i++) {
initData[i] = []; // that is filled with arrays
for (var j = 0; j < 12; j++) {
initData[i][j] = []; // which are filled with arrays
for (var k = 0; k < 2; k++) {
initData[i][j][k] = -1; // which are filled with numbers
}
}
}
or, to apply your loop unrolling:
var initData = [[], []]; // an array consisting of two arrays
for (var i = 0; i < 12; i++) {
// which each are filled with arrays that consist of two numbers
initData[0][i] = [-1, -1];
initData[1][i] = [-1, -1];
}
initData is a list of three lists, [2], [12] and [2]. Each one with one element.
In order to init a list(or array), you must do
var initData = [];
Then store in initData another list, like initData[0] = [] and so on... like it's mentioned, arrays/lists in javascript aren't initialized with a limit size.