I am trying to iterate over the variable pieces, but somehow it is not triggering. In the function below, pieces.length turns 4, but piecesNew turns [] - moreover console.log(i) is never reached.
What is happening?
self.reworkPieces = function(pieces) {
var piecesNew = [];
console.log(pieces.length)
for (var i; i <= pieces.length; i++) {
console.log(i)
piecesNew[i] = {
c: pieces[i].r,
r: pieces[i].c,
p: i
}
}
console.log(piecesNew)
return piecesNew;
};
undefined is not less than or greater than any number.
var i; // undefined
i < 10; // false
i > 10; // false
You simply need to make sure i is equal to 0.
You also want i to never be equal to pieces.length so use < instead of <= (the last index of an array is always length - 1, e.g. an array of length 3 has indexes 0, 1 and 2 – the first index is always 0, not 1)
So:
for (var i = 0; i < pieces.length; i++) {
...
define value for variable i, var i = 0
self.reworkPieces = function(pieces) {
var piecesNew = [];
console.log(pieces.length)
for (var i = 0; i <= pieces.length; i++) {
console.log(i)
piecesNew[i] = {
c: pieces[i].r,
r: pieces[i].c,
p: i
}
}
console.log(piecesNew)
return piecesNew;
};
self.reworkPieces = function(pieces) {
var piecesNew = [];
console.log(pieces.length)
for (var i = 0; i <= pieces.length; i++) {
console.log(i)
piecesNew[i] = {
c: pieces[i].r,
r: pieces[i].c,
p: i
}
}
console.log(piecesNew)
return piecesNew;
};
Change:
for (var i; i <= pieces.length; i++)
To:
for (var i = 0; i < pieces.length; i++)
Initialize var i = 0 initially then it will work
self.reworkPieces = function(pieces) {
var piecesNew = [];
console.log(pieces.length)
for (var i = 0; i <= pieces.length - 1; i++) {
console.log(i)
piecesNew[i] = {
c: pieces[i].r,
r: pieces[i].c,
p: i
}
}
console.log(piecesNew)
return piecesNew;
};
Related
So... If I input:
4 1 5 3
INSTEAD OF 1,3,4,5
I GET [ 4, 1, 5, 3 ]
Following is the code for merge sort but for the last comparison the program doesn't fetch updated (1,4) (3,5) value rather (4,1) (5,3) thus giving the wrong result.
var a = [4, 1, 5, 3];
q(a);
function q(a) {
var start = 0;
var n = a.length;
var length = parseInt(n / 2);
if (n < 2) {
return n;
}
var l = [], r = [];
for (i = 0; i < length; i++) {
l[i] = a[i]; //left array
}
for (i = 0, j = length; j < n; i++ , j++) {
r[i] = a[j]; //right array
}
q(l); //merge sort left array
q(r); //merge sort right array
comp(l, r);
}
function comp(l, r) {
var k = [], m = 0, i = 0, j = 0;
while (i < ((l.length)) && j < ((r.length))) {
if (l[i] < r[j]) {
k[m] = l[i];
i++;
m++
}
else {
k[m] = r[j];
j++;
m++
}
}
while (i != (l.length)) {
k[m] = l[i];
m++;
i++;
}
while (j != (r.length)) {
k[m] = r[j];
m++;
j++;
}
console.log(k); //for final output it is [ 4, 1, 5, 3 ] instead of [1,3,4,5]
}
You have a couple small problems. The main one is that you are returning the wrong thing from your edge condition:
if (n < 2) {
return n; // n is just a length; doesn't make sense to return it.
}
n is the length, you really want to return the small array here:
if (n < 2) {
return a; // return the array instead
}
Also, you need to pass the result of the recursive call to your comp function. Right now you're just returning the original lists with:
comp(l, r)
Something like this would work better:
let l_sort = q(l); //merge sort left array
let r_sort = q(r); //merge sort right array
return comp(l_sort, r_sort); // merge the arrays when recursion unwinds.
And you need to return things for recursion to work.
Put all together:
function q(a) {
var start = 0;
var n = a.length;
var length = parseInt(n / 2);
if (n < 2) {
return a;
}
var l = [],
r = [];
for (i = 0; i < length; i++) {
l[i] = a[i]; //left array
}
for (i = 0, j = length; j < n; i++, j++) {
r[i] = a[j]; //right array
}
let l_sort = q(l); //merge sort left array
let r_sort = q(r); //merge sort right array
return comp(l_sort, r_sort);
}
function comp(l, r) {
var k = [],
m = 0,
i = 0,
j = 0;
while (i < ((l.length)) && j < ((r.length))) {
if (l[i] < r[j]) {
k[m] = l[i];
i++;
m++
} else {
k[m] = r[j];
j++;
m++
}
}
while (i != (l.length)) {
k[m] = l[i];
m++;
i++;
}
while (j != (r.length)) {
k[m] = r[j];
m++;
j++;
}
return k
}
console.log(q([4, 1, 5, 3]).join(','));
console.log(q([5, 4, 3, 2, 1]).join(','));
console.log(q([2, 3]).join(','));
console.log(q([3, 2]).join(','));
console.log(q([1]).join(','));
I want to know what is wrong with this function that takes array and summation it's elements
var arr = [1,2,3,4,5,6,7,8,9,10];
var sum = 0;
var arraySum = function () {
for (var i = 0 ; i<= arr.length ; i++) {
sum += arr[i];
}
console.log(sum);
};
arraySum(arr);
You are trying to access an element outside of the array, this returns undefined.
for (var i = 0 ; i<= arr.length ; i++) {
// ^ the equal sign
replace it with
for (var i = 0 ; i< arr.length ; i++) {
var arr = [1,2,3,4,5,6,7,8,9,10];
var sum = 0;
var arraySum = function () {
for (var i = 0; i< arr.length; i++) {
sum += arr[i];
}
};
arraySum(arr);
document.write(sum);
The problem is there with your for loop's condition. Use < when you are checking against the length,
for (var i = 0 ; i < arr.length ; i++) {
//------------------^ replaced the <= with <
Your loop will iterate additionally one time, at that time the value will be undefined.
So sum + undefined = NaN.
If you want to use <= for sure then subtract 1 from the length and use it.
for (var i = 0 ; i <= arr.length-1 ; i++) {
//------------------------------^ decrement the length by 1
Or you can do the entire process with Array.prototype.reduce
var arr = [1,2,3,4,5,6,7,8,9,10];
var sum = arr.reduce((a, b) => { return a + b }, 0);
Also you can use Array.prototype.forEach function
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
var sum = 0;
arr.forEach(function(element) {
sum += element;
});
console.log(sum);
I am looking to create a function in javascript, which would allow me to pass a long array, together with one argument.
what I'm looking for is something like this:
var ar = [1,2,3,4];
var pairs = superAwesomeFunction(ar,2) //=> [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]];
var trebles = superAwesomeFunction(ar,3) //=> [[1,2,3],[1,2,4],[1,3,4],[2,3,4]
ideally, the function would have no limit on the folding argument.
I wrote a piece of code that looks like this, which is working fine, but it's not really useful as it isn't universal, and I would need a lot of such functions, which seems silly.
getAll2Folds: function (ar) {
var combinations = [],
numOdds = ar.length;
for (var i = 0; i < numOdds; i++) {
for (var j = i + 1; j < numOdds; j++) {
combinations.push([ar[i], ar[j]]);
}
}
return combinations;
},
getAll3Folds: function (ar) {
var combinations = [],
numOdds = ar.length;
for (var i = 0; i < numOdds; i++) {
for (var j = i + 1; j < numOdds; j++) {
for (var k = j + 1; k < numOdds; k++) {
combinations.push([ar[i], ar[j], ar[k]]);
}
}
}
return combinations;
};
},
... (not so great :|)
getAll8Folds: function (ar) {
var combinations = [],
numOdds = ar.length;
for (var i = 0; i < numOdds; i++) {
for (var j = i + 1; j < numOdds; j++) {
for (var k = j + 1; k < numOdds; k++) {
for (var l = k + 1; l < numOdds; l++) {
for (var m = l + 1; m < numOdds; m++) {
for (var n = m + 1; n < numOdds; n++) {
for (var o = n + 1; o < numOdds; o++) {
for (var p = o + 1; p < numOdds; p++) {
combinations.push([ar[i], ar[j], ar[k], ar[l], ar[m], ar[n], ar[o], ar[p]]);
}
}
}
}
}
}
}
}
return combinations;
}
I'm free to use underscore, jquery or whatever tool i want, but can't find an elegant solution, which would also be performant. ideas?
Thanks
Basically combine() takes an array with the values to combine and a size of the wanted combination results sets.
The inner function c() takes an array of previously made combinations and a start value as index of the original array for combination. The return is an array with all made combinations.
The first call is allways c([], 0), because of an empty result array and a start index of 0.
var arr = [1, 2, 3, 4, 5, 6, 7];
function combine(a, size) {
function c(part, start) {
var result = [], i, l, p;
for (i = start, l = arr.length; i < l; i++) {
// get a copy of part
p = part.slice(0);
// add the iterated element to p
p.push(a[i]);
// test if recursion can go on
if (p.length < size) {
// true: call c again and concat it to the result
result = result.concat(c(p, i + 1));
} else {
// false: push p to the result, stop recursion
result.push(p);
}
}
return result;
}
return c([], 0);
}
out(JSON.stringify(combine(arr, 2), null, 4), true);
out(JSON.stringify(combine(arr, 3), null, 4), true);
out(JSON.stringify(combine(arr, 4), null, 4), true);
out(JSON.stringify(combine(arr, 5), null, 4), true);
out(JSON.stringify(combine(arr, 6), null, 4), true);
// just for displaying the result
function out(s, pre) {
var descriptionNode = document.createElement('div');
descriptionNode.className = 'description';
if (pre) {
var preNode = document.createElement('pre');
preNode.innerHTML = s + '<br>';
descriptionNode.appendChild(preNode);
} else {
descriptionNode.innerHTML = s + '<br>';
}
document.getElementById('out').appendChild(descriptionNode);
}
<div id="out"></div>
This Javascript hangs browser when the number of iteration is set to 5. However, if set to 4, it runs normally. What is the problem?
var sample = [
[1,2,3],
[4,5,6],
[7,8,9]];
for(i = 0; i < 5; i++)
swapColumn(sample, 0, 1);
function swapColumn(array, x, y)
{
for(i = 0; i < array.length; i++)
{
temp = array[i][x];
array[i][x] = array[i][y];
array[i][y] = temp;
}
}
Don't forget to use var to declare variables
var sample = [
[1,2,3],
[4,5,6],
[7,8,9]];
for(var i = 0; i < 5; i++)
swapColumn(sample, 0, 1);
function swapColumn(array, x, y)
{
for(var i = 0; i < array.length; i++)
{
var temp = array[i][x];
array[i][x] = array[i][y];
array[i][y] = temp;
}
}
Otherwise they are treated as global variables, and you are actually overwriting i everytime you enter swapColumn
So, I'm working on a javascript application that can solve any size matrix. I'm running into a SUPER weird problem, where my main array only has the value of 0 after a certain point. The input should be a data set, like this
1, 8
2, 10
3, 13
4, 17
5, 22
But I'm having trouble with it. When I run the code, the console.log prints out a pretty derpy array
[[1, 1, 1, 8],
[0, 0, 0, 0],
[0, 0, 0, 0]]
It gets even weirder. If I move the console.log to before I call the rref function, I get the same thing.
Anybody ever seen this before? Anyone know how to fix it? Thanks!
//Matrix object
var matrix = {
startingDataSet: [],
degree: 0,
M: []
}
//splits up user input into a more readable format
function getDataFromString(data) {
var points = data.split("\n");
for (var i=0; i<points.length; i++) {
points[i] = points[i].split(", ");
points[i][0] = parseInt(points[i][0]);
points[i][1] = parseInt(points[i][1]);
}
return points;
}
//finds the degree of the polynomail from the matrix object's data
function setPolynomialDegree(original) {
var data = original;
console.log(original);
//temporary data set to hold numbers in
var tempNumbers = [];
var degree = 1;
//move the original set of Y values into the temporary data set
for (var i = 0; i < data.length; i++) {
tempNumbers.push(data[i][1]);
}
//while the numbers in tempdata are not the same, execute subtraction
while (tempNumbers[0] != tempNumbers[1]) {
var newnums = []
var l = tempNumbers.length;
//find the difference for every set of numbers (0 & 1, 1 & 2, 2 & 3, etc.), and push those into the new data set
for (var i = 0; i < l - 1; i++) {
newnums.push(tempNumbers[i + 1] - tempNumbers[i]);
}
//replace old data set with new one
tempNumbers = newnums;
//increase polynomial degree by one
degree += 1;
}
return degree;
}
//add 2 arrays together
function addrows(r1, r2) {
var temprow = [];
for (var i = 0; i < r1.length; i++) {
temprow.push(r1[i] + r2[i]);
}
return temprow;
}
//multiply array by constant
function multrow(r1, num) {
var temprow = [];
for (var i = 0; i < r1.length; i++) {
temprow.push(r1[i] * num);
}
return temprow;
}
//rref function
function rref(mtrx, deg) {
var temp1 = [];
var temp2 = [];
for (var row = 0; row < mtrx.length; row++) {
for (var j = 0; j < mtrx.length-1; j++) {
temp1 = multrow(mtrx[row], mtrx[j+1][row]);
temp2 = multrow(mtrx[j+1], mtrx[row][row]);
temp1 = multrow(temp1, -1);
mtrx[j+1] = addrows(temp1, temp2);
}
}
return mtrx;
}
//Main function that will solve the matrix
function solveFromDataSet(data) {
data = getDataFromString(data);
for (var i=0; i<data.length; i++) {
matrix['startingDataSet'].push(data[i]);
}
matrix.degree = setPolynomialDegree(matrix.startingDataSet);
matrix.M = [];
for (var i = 0; i < matrix.degree; i++) {
var row = [];
for (var j = matrix.degree; j > 0; j--) {
row.push(Math.pow(data[i][0], j - 1));
}
row.push(data[i][1]);
matrix['M'][i] = row;
}
var var_array = rref(matrix['M']);
console.log(matrix.M);
return matrix.M;
}