I have an array that contains elements my goal is to slice some of the elements inside the array, then later I want to reassign the original array with a new array which is a sublist of the original array but it seems like I can't make that happen please help.
let arr = [1,2,3,4,5]
function subList(arr){
for(let i = 0; i < arr.length; i++){
let res = arr.slice(0,i)
if(i === 3){
arr = res;
}
}
}
subList(arr)
console.log(arr)
// expected output [1,2,3]
There are a lot of ways to do it.
Why it isn't working for you:
You are passing the arr into the variable and since it is an object ideally any change you make to it should be reflected outside. But you aren't actually mutating/changing anything in your passed argument, you are reassigning it (with arr=res). So that will not make any change to the arr outside.
If you do something like .push(),.pop(), which are operations on the array without reassigning it, that should actually change it.
Example modifying your code with operations that actually modify the array instead of replacing it splice() , push:
let arr = [1,2,3,4,5]
function subList(arr){
for(let i = 0; i < arr.length; i++){
let res = arr.slice(0,i)
if(i === 3){
arr.splice(0,arr.length);
arr.push(...res);
break;
}
}
}
subList(arr)
console.log(arr)
Pass in an index to the function and just return arr.slice(0, i);.
let arr = [1, 2, 3, 4, 5]
function subList(arr, i) {
return arr.slice(0, i);
}
console.log(subList(arr, 3));
let list = [1,2,3,4,5]
function subList(arr,n){
for(let i = 0; i < arr.length; i++){
if(i === 3){
let res = arr.slice(0,i)
list = res;
}
}
}
subList(list,0)
console.log(list)
Related
This question already has answers here:
How can I remove a specific item from an array in JavaScript?
(142 answers)
Closed 1 year ago.
How can I check whether an array contains a value, and if so, remove it?
PS: For this exercise, I'm not allowed to use anything more than than .pop, .push and .length array functions.
My logic is the following: if the specified value is within the array, reorder the array so that the last element of it will contain this value, then remove it with .pop. But how can I find this value and reorder it without using anything more than those array functions I specified above?
This is what I managed to come up with so far:
let array_1 = [1,2,3];
if (array_1 == 2){
//reorder somehow
array_1.pop();
}
console.log(array_1);
Using this approach, you are not creating a new array but modifying it. It uses .pop().
let array_1 = [1, 2, 3];
// Iterate all array
for (let i = 0; i < array_1.length; i++) {
// While there is a 2 element in the actual index, move all elements (from i index) to the previous index
while(array_1[i] === 2) {
for (let j = i; j < array_1.length - 1; j++) {
array_1[j] = array_1[j + 1];
}
// Now remove the last element (since we move all elements to the previous index)
array_1.pop();
}
}
console.log(array_1);
Here a snippet so you can try it
let array_1 = [1, 2, 3, 4, 2, 5, 2, 6, 2];
for (let i = 0; i < array_1.length; i++) {
while(array_1[i] === 2) {
for (let j = i; j < array_1.length - 1; j++) {
array_1[j] = array_1[j + 1];
}
array_1.pop();
}
}
console.log(array_1);
This would mantain the order of the array, but without the "2" elements.
Here's another option using pop
const filter = (array, target) => {
const newArray = [];
let tmp;
while(tmp = array.pop()) {
if (tmp !== target) {
newArray.push(tmp)
}
}
console.log(newArray)
return newArray;
}
filter([1,2,3,4], 2) // [4, 3, 1] Note that it reversed the order of the array!
If you are limited to pop, push and length, you can loop over all elements, check if a given element matches the value you are looking for, and add them to a new array using push.
let array_1 = [1,2,3];
let newArray = [];
for (let i = 0; i < array_1.length; i++) {
if (array_1[i] !== 2) {
newArray.push(array_1[i]);
}
}
console.log(newArray);
// using splice
// splice(indexStart, how many, replace with)
// example :
let arr = [0,1,2,3,4,5];
// remove at index 1
arr.splice(1,1);
console.log( arr );
// replace at index 1
arr.splice(1,1,"new 1");
console.log( arr );
// merge index 2 and 3
arr.splice(2,2,"merge 2 and 3");
console.log( arr );
// create 2 new items start at index 2
arr.splice(2,2,"new 2", "new 3");
console.log( arr );
I've been trying and searching how to loop through the params to check if those already exist in an array, i haven't got it fully working but when there is a duplicate value it dose not return at all.
The idear is pass multiple values is param then loop through those vals and only push if it dose not exist in the array.
var arr = [7,3,1];
function pushNew(obj) {
var prams = obj;
for(var k = 0; k < obj.length; k++){
for (var i = 0; i < arr.length; i++) {
if (arr[i] == prams[k]) {
return;
}
}
array.push(prams[k]);
}
// console.info(arr);
}
pushNew([2,7,4]);
A short and more modern way to just get all the unique values is to use Array.from with Set. A Set is an array-like structure that will only hold unique values. Array.from converts an array-like structure into a real array.
In your case, you can just concat both arrays, pass them to Set to remove the duplicates, and use Array.from to convert it back to a regular array.
var arr1 = [1, 2, 3, 4, 5];
var arr2 = [3, 4, 5, 6, 7];
var result = Array.from(new Set(arr1.concat(arr2)));
document.write(JSON.stringify(result));
Actually, your existing code nearly works.
You can set a flag if you find a match in the inner loop and instead of return you should use break to escape the loop. Then use push after the inner loop if a match wasn't found. Also, there is no need for both obj and prams (which I've renamed to params), so:
var arr = [7,3,1];
function pushNew(params) {
var found;
for(var k=0; k<params.length; k++){
// Set found to initial value on each outer loop
found = false;
for (var i=0; i<arr.length; i++) {
// If find match, set flag and break from loop (for efficiency)
if (arr[i] == params[k]) {
found = true;
break;
}
}
// If match not found, push into arr
if (!found) arr.push(params[k]);
}
}
pushNew([7,2])
document.write(arr); // 7,3,1,2
If you want efficient code, consider creating an index and using in:
var arr = [7,3,1];
function addParams(params) {
var index = arr.reduce(function(acc, v) {
acc[v] = true;
return acc;
},{});
params.forEach(function(v) {
if (!(v in index)) arr.push(v);
});
}
addParams([7,3,2]);
document.write(arr);
You can use indexOf to validate if element is present in an array. forEach is another array method which works like loop.
var arr = [7,3,1];
function pushNew(obj) {
//var prams = obj;
obj.forEach(function(item){ // iterate through each element
if(arr.indexOf(item) == -1){ //indexOf return -1 is element is not present in an array
arr.push(item)
}
})
console.log(arr);
}
pushNew([2,7,4]);
Working Jsfiddle
var arr = [7, 3, 1];
function pushNew(obj) {
for (var k = 0; k < obj.length; k++) {
if (arr.indexOf(obj[k]) == -1) {
arr.push(obj[k]);
}
}
}
pushNew([2, 7, 4]);
You can use _.union function of lodash.
_.union([2, 1], [4, 2], [1, 2]);
// → [2, 1, 4]
I am working on a code where I need to reverse certain no of elements in an array and rest should remain same. For example is an array has values of 1,2,3,4,5,6 and I have to reverse 4 elements of it then output should be 4,3,2,1,5,6. I am using below code to achieve this but getting error, please suggest.
function reverseArray(n, a) {
var interimArray1 = [];
//var interimArray2=[];
//var finalArray=[];
for (var i < n; i >= 0; i--) {
interimArray1.push[a[i]];
}
for (var i = n; i < a.length; i++) {
interimArray1.push[a[i]];
}
for (var i = 0; i < interimArray1.length; i++) {
console.log(interimArray1[i]);
}
}
var arr = [1, 2, 3, 4, 5, 6];
var num = 4;
reverseArray(num, arr);
The error in your code is that you intend to call the push method on a[i] like so:
interimArray1.push(a[i]);
but instead you write:
interimArray1.push[a[i]];
You make that mistake twice. To give arguments to the push method, you must use round parenthesis ().
With that fixed, you will see that your code works perfectly.
You can use Array#slice, Array#splice as follow.
function partialReverse(arr, num, from = 0) {
var slicedArr = arr.slice(from, num + from);
arr.splice(from, num); // Remove `num` items from array
arr.splice(from, 0, ...slicedArr.reverse()); // Add `num` reversed items
return arr;
}
var arr = [1, 2, 3, 4, 5, 6];
console.log(partialReverse(arr, 4, 0)); // Reverse four items from `arr` starting from 0th index
console.log(partialReverse(arr, 4, 1)); // Reverse four items from `arr` starting from 1st index
Lots of hints but you seem to be missing them. ;-)
You need to assign an initial value to i, so:
for (var i = n; ... )
===========^
Also, you need to use () to call functions, not [], so:
interimArray1.push(a[i]);
==================^====^
Same in the following for block. Otherwise, the code works though it's more verbose than it needs to be.
This is working :
I'm sure there are faster ways of doing it. Also, it will only work for elements at the beginning of the array but you can adjust the function for what you want to achieve.
var reverseArray = function(arr,elementsToReverse) {
var tempArrayRev = [];
var tempArray = [];
for (var i=0;i<arr.length;i++) {
if (i < elementsToReverse) {
tempArrayRev[i] = arr[i];
} else {
tempArray.push(arr[i]);
}
}
return tempArrayRev.reverse().concat(tempArray);
}
var array = [1,2,3,4,5,6];
document.getElementById('arrayOutput').innerHTML += reverseArray(array,4);
<div id="arrayOutput">Array :<br></div>
This is the answer you can test it.
function reverseArray(n, a) {
var interimArray1 = [];
for (var i = 0; i < a.length; i++) {
interimArray1.push(a[i]);
}
for (var i = num; i >=0; i--) {
interimArray1[i-1] = a[n - i];
}
for (var i = 0; i < interimArray1.length; i++) {
console.log(interimArray1[i]);
}
}
var arr = [1, 2, 3, 4, 5, 6];
var num = 4;
reverseArray(num, arr);
You could use something like this.
function reverseArray(n, arrIn) {
// Splice splits the array in 2 starting at 0 index going n long
var arrOut = arrIn.splice(0,n);
// reverse is pretty straight forward
arrOut = arrOut.reverse();
// Concat joins the two together
return arrOut.concat(arrIn);
}
I have an array and an array of objects. I want to search each value in the array in the array of objects and if it doesnt exist, I want to remove the value from the array.
var arr= [1,2,3,4];
var recs = [{id:1},{id:2},{id:3}]; //4 doesnt exist in recs, remove from arr
//arr = [1,2,3];
Heres my attempt. Obviously does not work. I am not sure how I can compare each arr index with all the values in recs before moving on the next arr index:
var arr= [1, 2, 3, 4], index;
var recs = [{a:1},{a:2},{a:3}];
for(var i = 0; i<arr.length; i++){
for(var val in recs[i]){
if(arr[i] != recs[i][val]){
index = arr.indexOf(arr[i]);
arr.splice(index, 1);
}
}
}
thank you!!
If you are okay with leaving your original array instance alone and creating a new one (essentially treating it as immutable)
var newArr = arr.filter(function(num) {
return !recs.every(function(obj) {
return obj.a !== num;
});
});
Detail of the methods used: Array.filter is passed a function, runs that function on each element inside, and then returns a new array with only the elements that returned true in the function.
Array.every works a little similar, but returns a Boolean, true or false. It returns true if all of the elements of the array returned true inside of the function.
var arr= [1, 2, 3, 4];
var recs = [{a:1},{a:2},{a:3}];
// don't use var in for loops.
// Variables declared with var have function scope, so declare them at the top of your function
var i;
var j;
var value;
var found;
// iterate over the array
for (i = 0; i < arr.length; i++)
{
value = arr[i];
found = false;
// iterate over the other array
for (j = 0 ; j < recs.length ; j++)
{
// if we found what we were looking for, make a note and exit loop
if (recs[j].a == value)
{
found = true;
break;
}
}
if (!found)
{
arr.splice(i, 1);
// To compensate the loop's i++, to avoid skipping the next entry
i--;
}
}
alert(arr.join(','));
How can I remove an object from a copy of an array without removing it from the original?
I have a global variable :
var userTrickList = [];
And inside a function, I make a copy of that global array :
var tempUserTrickList = userTrickList;
Then I use the removeItem function that I created to remove a certain object.
removeItem(considerTrick.IDName, tempUserTrickList);
function removeItem(item, list) {
//takes a string as 'item', finds in the array as 'list',
//then removes it from the list.
for(var i = 0; i < list.length; i++)
{
if(item === list[i])
{
list.splice(i,1);
}
}
}
My problem is, this function removes it from the userTrickList too.
Any ideas? It's definitely a problem in "removeItem(considerTrick.IDName, tempUserTrickList);", but I can't think of a solution.
Use .slice(0) to clone an array.
var tempUserTrickList = userTrickList.slice(0);
Credits:
http://davidwalsh.name/javascript-clone-array
use this function for your requirement
function removeElementFromArray(data,target) {
var temp=new Array();
for ( var i = 0; i < data.length; i++) {
if(data[i]!=target){
temp.push(data[i]);
}
}
return temp; }
here data is original array and target is the element you want to remove from array
this function will return array without containing the removed item.
Try, It copy the original array
var tempUserTrickList = JSON.parse(JSON.stringify(userTrickList));
Demo CopyArray
for (i = 0, l = arr.length; i < l; i++) {
if (arr[i] === item) {
arr.splice(i, 1);
i -= 1;
l -= 1;
}
}
Daniel's method of cloning an array is absolutely correct, but since I don't see an ES6-oriented answer, I'll offer up an alternative solution:
We can just as easily use the spread operator to clone an array, so we don't have to use the slice call.
const arr = [1, 2, 3];
const copy = [...arr];
copy.pop();
console.log(arr); // returns [1, 2, 3]
console.log(copy); // returns [1, 2]