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I have an array that looks like this:
arr = [[1,2,3],
[4,5,6],
[7,8,9]]
I have initialized an empty array and I want put the diagonals of the arr inside the new array. So i've tried this:
arr = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
new_arr = [];
tail = arr.length - 1;
for (let i = 0; i < arr.length; i++) {
for (let j = 0; j < arr[i].length; j++) {
if (j == i) {
new_arr.push(arr[i][j]);
}
if (j == tail) {
new_arr.push(arr[i][j]);
tail--;
}
}
}
console.log(new_arr)
The logic seems to work but I can't seem to get the structure right. What I want is to nest two arrays inside the new array like this:
[[1,5,9],[3,5,7]]
But what I get is one array with the right values unordered. How to get the expected output? Any help is appreciated. Thanks!
You need to have 2 separate temporary arrays. And you don't need nested loops. You can optimize the code like this with a single loop if you understand the math.
arr = [[1,2,3],
[4,5,6],
[7,8,9]];
function findDiagonals(arr) {
const diagonal_1 = [];
const diagonal_2 = [];
for( let i = 0; i < arr.length; i++ ) {
diagonal_1.push(arr[i][i]);
diagonal_2.push(arr[i][arr.length - (i+1)]);
}
return [diagonal_1, diagonal_2];
}
console.log(findDiagonals(arr));
var arr = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
];
var diagonal1 = [];
var diagonal2 = [];
for (var i = 0; i < arr.length; i++) {
diagonal1.push(arr[i][i]);
diagonal2.push(arr[i][arr.length - i - 1]);
}
var new_arr = [diagonal1, diagonal2];
console.log(new_arr)
The following solution would work for you if the width and height of the number matrix is always equal.
const arr = [[1,2,3],
[4,5,6],
[7,8,9]];
const result = [[],[]];
arr.map((row,index) => {
result[0].push(row[0+index]);
result[1].push(row[row.length - index - 1]);
});
console.log(result); // [[1,5,9],[3,5,7]]
This is a O(n) approach by using the function Array.prototype.reduce.
const arr = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
];
const result = arr.reduce(([left, right], array, row, {length}) => {
return [[...left, array[row]], [...right, array[length - row - 1]]];
}, [[],[]]);
console.log(result);
.as-console-wrapper { max-height: 100% !important; top: 0; }
the difficulty is low:
const
arr = [[1,2,3],[4,5,6],[7,8,9]]
, new_arr = [[],[]]
;
let p0 = 0, p1 = arr.length
for( let inArr of arr)
{
new_arr[0].push( inArr[p0++] )
new_arr[1].push( inArr[--p1] )
}
console.log( JSON.stringify( new_arr ))
in a one Line code:
const
arr = [[1,2,3],[4,5,6],[7,8,9]]
, new_arr = arr.reduce(([lft,rgt],A,i,{length:Sz})=>([[...lft,A[i]],[...rgt,A[Sz-i-1]]]),[[],[]])
;
console.log( JSON.stringify( new_arr )) // [[1,5,9],[3,5,7]]
My task is to split the given array into smaller arrays using JavaScript. For example [1, 2, 3, 4] should be split to [1] [1, 2] [1, 2, 3] [1, 2, 3, 4] [2] [2, 3] [2, 3, 4] [3] [3, 4] [4].
I am using this code:
let arr = [1, 2, 3, 4];
for (let i = 1; i <= arr.length; i++) {
let a = [];
for (let j = 0; j < arr.length; j++) {
a.push(arr[j]);
if (a.length === i) {
break;
}
}
console.log(a);
}
And I get the following result: [1] [1, 2] [1, 2, 3] [1, 2, 3, 4] undefined
What am I missing/doing wrong?
For the inner array, you could just start with the index of the outer array.
var array = [1, 2, 3, 4],
i, j, l = array.length,
result = [];
for (i = 0; i < l; i++) {
for (j = i; j < l; j++) {
result.push(array.slice(i, j + 1));
}
}
console.log(result.map(a => a.join(' ')));
.as-console-wrapper { max-height: 100% !important; top: 0; }
You have two issues in your code:
You need to have loop to initialize with the value of i for the inner loop so that it consider the next index for new iteration of i
You need to remove that break on the length which you have in inner loop.
let arr = [1, 2, 3, 4];
for (let i = 0; i <= arr.length; i++) {
let a = [];
for (let j = i; j < arr.length; j++) {
a.push(arr[j]);
console.log(a);
}
}
Try this
let arr = [1, 2, 3, 4];
for (let i = 0; i <= arr.length; i++) {
let a = [];
for (let j = i; j < arr.length; j++) {
a.push(arr[j]);
console.log(a);
}
}
If you don't want to mutate your array.
let arr = [1, 2, 3, 4];
let res = [];
for (let i = 0; i <= arr.length; i++) {
let a = [];
for (let j = i; j < arr.length; j++) {
a = [...a, arr[j]];
res = [...res, a];
}
}
console.log(res);
i have prepare stackblitz for this case.
let source = [1,2,3,4];
const output = [];
const arrayMultiplier = (source) => {
const eachValueArray = [];
source.forEach((item, index) => {
// Will push new array who will be sliced source array.
eachValueArray.push(source.slice(0, source.length - index));
});
//We reverse array to have right order.
return eachValueArray.reverse();
};
for(let i = 0; i <= source.length; i++) {
output.push(...arrayMultiplier(source));
source.shift(); // Will recraft source array by removing first index.
}
//Don't forget last item.
output.push(source);
console.log(output);
Is not the most shorten solution but do the job
== update after code review ==
// [...]
const arrayMultiplier = (source) => {
// Will push new array who will be sliced source array.
// We reverse array to have right order.
return source.map((item, index) => source.slice(0, source.length - index)).reverse();
};
// [...]
Use two iteration
get slice array based on loop index.
use sliced array and combine array element.
var arr = [1, 2, 3, 4];
let newArra =[];
arr.map((x,i)=> {
let remainArr = arr.slice(i);
return remainArr.forEach((y, r) => newArra.push(remainArr.slice(0, r+1)))
})
newArra.forEach(x=> console.log(x))
Here is the question:
Compare two arrays and return a new array with any items only found in one of the two given arrays, but not both. In other words, return the symmetric difference of the two arrays.
And here is my code:
function diffArray(arr1, arr2) {
var newArr = [];
// Same, same; but different.
for (i = 0; i < arr1.length; i++) {
for (j = 0; j < arr2.length; j++)
while (arr1[i] === arr2[j])
delete arr2[j];
newArr = arr2;
}
return newArr;
}
console.log(diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]));
Please, tell me my mistakes.
If you work using indices as references which you delete, you'll leave those indices undefined.
You have to use push to add an item and splice to remove one.
The time complexity of the following code should be: O(nm) where n and m are the lengths of the arr1 and arr2 arrays respectively.
function diffArray(arr1, arr2) {
var newArr = [];
for (i = 0; i < arr1.length; i++) {
for (j = 0; j < arr2.length; j++)
while (arr1[i] === arr2[j])
arr2.splice(j, 1);
newArr = arr2;
}
return newArr;
}
console.log(diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]));
This should work, but I've found a different way that is a bit slower for short arrays but much faster for longer array.
The time complexity of the following code should be: O(3(n + m)), which is reduced to O(n + m) where n and m are the lengths of the arr1 and arr2 arrays respectively.
Look at this fiddle.
Here's it:
function diffArray(arr1, arr2) {
let obj1 = {}, obj2 = {};
for (let l = arr1.length, i = 0; i < l; i++)
obj1[arr1[i]] = undefined;
for (let l = arr2.length, i = 0; i < l; i++)
obj2[arr2[i]] = undefined;
let a = [];
for (let arr = arr1.concat(arr2), l = arr.length, i = 0, item = arr[0]; i < l; i++, item = arr[i])
if (item in obj1 !== item in obj2)
a.push(item);
return a;
}
console.log(diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]));
The task you are trying to complete asks you to create a new array, but instead you modify arr2. It would probably be easiest to just copy all elements not included in the other array to a new array, like this:
function diffArray(arr1, arr2) {
var newArray = [];
arr1.forEach(function(el) {
if (!arr2.includes(el)) {
newArray.push(el);
}
});
arr2.forEach(function(el) {
if (!arr1.includes(el)) {
newArray.push(el);
}
});
return newArray;
}
If you would rather try and fix your code instead, I can try to have another look at it.
I've used Array.prototype.filter method:
function diffArray(arr1, arr2) {
var dif01 = arr1.filter(function (t) {
return arr2.indexOf(t) === -1;
});
var dif02 = arr2.filter(function (t) {
return arr1.indexOf(t) === -1;
});
return (dif01).concat(dif02);
}
alert(diffArray([1, 2, 3, 6, 5], [1, 2, 3, 4, 7, 5]));
If you still want to use your code and delete the common elements, try to use Array.prototype.splice method instead of delete: the latter deletes the value, but keeps the index empty, while Array.prototype.splice will remove those whole indices within the given range and will reindex the items next to the range.
You can use Array.prototype.filter:
var array1 = [1, 2, 3, 5];
var array2 = [1, 2, 3, 4, 5];
var filteredArray = filter(array1, array2).concat(filter(array2, array1));
function filter(arr1, arr2) {
return arr1.filter(function(el) { return arr2.indexOf(el) < 0; });
}
Here is a working JSFiddle.
Try this:
function diffArray(arr1, arr2) {
var ret = [];
function checkElem(arrFrom, arrIn) {
for (var i = 0; i < arrFrom.length; ++i) {
var elem = arrFrom[i];
if (arrIn.indexOf(elem) === -1)
ret.push(elem);
}
}
checkElem(arr1, arr2);
checkElem(arr2, arr1);
return ret;
}
I hope this can solve your problem.
I have an array that has some values inside, and I wish to return another array that has the value grouped in to their own arrays.
So the result I am trying to achieve is something like this:
var arr = [1,1,2,2,2,3,3,4,4,4,4,5,6]
var groupedArr =[[1,1],[2,2,2],[3,3],[4,4,4,4],[5],[6]]
This proposal works with Array#reduce for sorted arrays.
var arr = [1, 1, 2, 2, 2, 3, 3, 4, 4, 4, 4, 5, 6],
groupedArr = arr.reduce(function (r, a, i) {
if (!i || a !== r[r.length - 1][0]) {
return r.concat([[a]]);
}
r[r.length - 1].push(a);
return r;
}, []);
document.write('<pre>' + JSON.stringify(groupedArr, 0, 4) + '</pre>');
Here you go. By the way, this works with unsorted array as well.
var arr = [1, 1, 2, 2, 2, 3, 3, 4, 4, 4, 4, 5, 6]
var grpdArr = [];
while(arr.length > 0){
var item = arr[0];
grpdArr.push(arr.filter(function(val) {
return val === item;
}));
arr = arr.filter(function(val){return val!==item});
}
//console.log(arr, grpdArr);
Well this should do. Pretty straight forward..,
You get the elements and then remove them.
With forEach and temporary array
var arr = [1, 1, 2, 2, 2, 3, 3, 4, 4, 4, 4, 5, 6];
var temp = [];
var res = [];
arr.forEach(function(e) {
if (temp.slice(-1) == e) temp.push(e);
else {
temp = [e];
res.push(temp);
}
});
document.write(JSON.stringify(res));
This may not be the most optimal version but should do. This also works for unsorted arrays.
function abc(arr) {
var newObj = new Object();
for (var i in arr) {
if (typeof newObj[arr[i]] == 'undefined') {
newObj[arr[i]] = new Array();
}
newObj[arr[i]].push(arr[i]);
}
var groupedArr = new Array();
for (i in newObj) {
groupedArr.push(newObj[i]);
}
return groupedArr;
}
console.log(abc([1, 1, 2, 2, 3, 3, 3, 4, 1]));
This is the most straightforward in my mind:
var arr = [1,1,2,2,2,3,3,4,4,4,4,5,6];
var grouped = {};
var groupedArr = [];
//accumulate the values in an object, each key is an array
for (var i = 0; i < arr.length; i++) {
if (!grouped[arr[i]]) grouped[arr[i]] = [];
grouped[arr[i]].push(arr[i]);
}
//loop through all the keys in the object and push the arrays to the master array
var keys = Object.keys(grouped);
for (var i = 0; i < keys.length; i++) {
groupedArr.push(grouped[keys[i]]);
}
console.log(groupedArr);
I think you could use the code below:
var arr = [1,1,2,2,2,3,3,4,4,4,4,5,6]
var groupedArray = [];
var temp = arr.sort();
var tempArray = [arr[0]];
for(var i = 0; i < temp.length - 1; ++i){
if(temp[i] == temp[i + 1]){
tempArray.push(temp[i + 1]);
}else{
groupedArray.push(tempArray);
tempArray = [temp[i + 1]];
}
}
groupedArray.push(tempArray);
Now the groupedArray will contain the Result
I encountered a problem!
for example! here is my 2 dimensional array: var array=[[1,2,3,4],[2,3,4,5],[3,4,5,6]];
and my desired outcome is : [[1,2,3,4],[2,3,4,5],[3,4,5,6],[6,9,12,15]]
the [6,9,12,15] came from adding the same index numbers of the previous inner arrays. (ex 1+2+3, 2+3+4, 3+4+5, 4+5+6 more clear : index 1 + index 1+ index1 produces 9)
I am so confused so far, the closes i did was to sum up [1,2,3,4][2,3,4,5][3,4,5,6], but I cant seem to do something with each and individual numbers :(
The question requested me to do nested for loops, So i cant use any thing like reduce, map, flatten, etc...
try with this way:https://jsfiddle.net/0L0h7cat/
var array=[[1,2,3,4],[2,3,4,5],[3,4,5,6]];
var array4 = [];
for (j = 0; j < array[0].length; j++) {
var num =0;
for(i=0;i< array.length;i++){
num += array[i][j];
}
array4.push(num);
}
array.push(array4);
alert(array);
Just iterate over the outer array and the inner arrays and add the values to the result array array[3].
var array = [[1, 2, 3, 4], [2, 3, 4, 5], [3, 4, 5, 6]];
array.forEach(function (a) {
a.forEach(function (b, i) {
array[3] = array[3] || [];
array[3][i] = (array[3][i] || 0) + b;
});
});
document.write('<pre>' + JSON.stringify(array, 0, 4) + '</pre>');
https://jsfiddle.net/0L0h7cat/
var array = [
[1, 2, 3, 4],
[2, 3, 4, 5],
[3, 4, 5, 6]
];
var sumArr = [];
for (var i = 0; i < array[0].length; i++) {
sumArr[i] = 0;
for (var j = 0; j < array.length; j++)
sumArr[i] += array[j][i];
}
array.push(sumArr);
If you are interested in Arrow Functions, this will work:-
var array = [[1, 2, 3, 4],[2, 3, 4, 5],[3, 4, 5, 6]];
var count = [];
array.forEach(x => x.forEach((y, i) => count[i] = (count[i] || 0) + y));
array.push(count);
console.log(array);
NOTE: Not cross browser support yet.
This is how -
var array=[[1,2,3,4],[2,3,4,5],[3,4,5,6]];
var array2=[]
for (var i = array[0].length;i--;) {
var sum=0;
for (var j = array.length; j--;) {
sum=sum+array[j][i];
}
array2.push(sum)
}
array.push(array2.reverse());
document.write('<pre>'+JSON.stringify(array) + '</pre>');
But I'm sure there are more elegant methods. I'm just learning by answering questions myself.
A simplistic approach with just conventional for loops
var input = [[1,2,3,4],[2,3,4,5],[3,4,5,6]];
function getSumOfArrayOfArrays(inputArray) {
var length = inputArray.length;
var result = [];
for(var i=0; i<length; i++){
for(var j=0; j<=3; j++){
result[j] = result[j] ? result[j] + inputArray[i][j] : inputArray[i][j];
}
}
return result;
}
var output = getSumOfArrayOfArrays(input); // [6,9,12,15]
var desiredOutput = input;
desiredOutput.push(output)
document.write(JSON.stringify(desiredOutput));
// [[1,2,3,4],[2,3,4,5],[3,4,5,6],[6,9,12,15]]
I try to avoid writing nested for loops.
var arrayOfArrays=[
[1,2,3,4],
[2,3,4,5],
[3,4,5,6]
];
//define a function to extend the Array prototype
Array.prototype.add = function(otherArray){
var result = [];
for(var i = 0; i < this.length; i++) {
result.push( this[i] + otherArray[i] )
}
return result;
};
//reduce array of arrays to get the result array `sum`
var sum = arrayOfArrays.reduce(function(arrayA, arrayB){
//`arrayA`+`arrayB` becomes another `arrayA`
return arrayA.add(arrayB)
});
//put `sum` back to `arrayOfArrays`
arrayOfArrays.push(sum);
document.write('<pre>' + JSON.stringify(arrayOfArrays) + '</pre>');