So today I was learning about some ES6 array helpers, and I wanted to change my existing for loops with them, but I can not get same result as i was taking with for loop
function comment(){
let index;
for(let i = 0; i < commentArray.length; i++){
if(commentArray[i]._id == req.params.commentId){
index = commentArray.indexOf(commentArray[i]);
}
}
return index;
}
var com = comment();
It is nodejs and I am trying to get element index from database, and than pull from it, my code works just fine, but I want to change it with array helper, I guess I need find helper, but I can not make it work!
You can replace your for loop with this one-liner which uses Array#findIndex:
let index = commentArray.findIndex(comment => comment._id === req.params.commentId);
When this line executes, it will assign the index of comment, which has _id attribute same as req.params.commentId.
If you want to find the index of the item in the array based on some condition, you can use findIndex function
commentArray.findIndex(comment => comment._id === req.params.commentId)
Also with your current code with for loop, I think you need return the index as soon as it is found and not let the loop iterate till the end.
for(let i = 0; i < commentArray.length; i++){
if(commentArray[i]._id == req.params.commentId){
return commentArray.indexOf(commentArray[i]);
}
}
Related
ı couldn't pop() every array list. at the end remain two array elements
function ürünSil(){
let diller = [ "Türkçe", "İngilizce", "Almanca", "Fransızca", "Japonca"]
for(let i in diller){
let sonİcerik = diller.pop()
document.write(diller + "<br />")
}
}
you can empty your array like this also:
let diller = [ "Türkçe", "İngilizce", "Almanca", "Fransızca", "Japonca"];
while(diller.length > 0) {
diller.pop();
}
console.log(diller)
The length of the array changes each time on pop() so when there are 3 items removed from the array , the present index for i on your code will be 2 and hence the actual length is also 2, so the for() loops does not trigger further.
The solution could be to preserve the initial length value and use that value in the loop:
function ürünSil(){
let diller = [ "Türkçe", "İngilizce", "Almanca", "Fransızca", "Japonca"]
const length = diller.length;
for(let i = 0; i<length; i++){
let sonİcerik = diller.pop()
console.log(sonİcerik);
}
}
ürünSil()
use while loop instead of for.
while (diller.length != 0) {
diller.pop();
document.write(diller + '<br />');
}
This happens because pop reduces the length of the array, which impacts the times the loop will iterate. Instead just have the while condition check whether the array still has elements, without any i.
Unrelated, but
don't use document.write for this. Use console.log, or if you want to add data to the HTML document, then use other DOM methods.
have the good habit of ending your statements with semicolon. You don't want to fall for the sometimes tricky effects of automatic semicolon insertion.
let diller = [ "Türkçe", "İngilizce", "Almanca", "Fransızca", "Japonca"];
while (diller.length) {
let sonİcerik = diller.pop();
console.log(sonİcerik);
}
I'm working on a problem where I need to find all the power set of a given string which are all the possible subsets. I feel like I'm close with my current code but I can't figure out why I'm getting stuck on an infinite loop for my second iteration. I ran it through the debugger but I still can't seem to figure it out even though I'm sure it's very simple. When i = 0 then it goes to the second loop where j = 0 && j < 1 so for example if help is my given str argument then I would expect it to add j + '' and push it into my allSubsets array. The problem is that the j iteration will keep looping and doing j++ and will never stop. I'm not sure why this is. One particular question even if I solve this infinite loop - do I need to update the allSubsets.length in the iteration to keep it updated with the pushed in strings?
var powerSet = function(str) {
let allSubsets = [''];
for (let i = 0; i < str.length; i++) {
debugger;
for (let j = 0; j < allSubsets.length; j++) {
allSubsets.push(sortLetters(str[i] + allSubsets[j]));
}
}
return allSubsets;
};
var sortLetters = (word => {
//convert string to an array
//use the sort to sort by letter
//convert array back to string and return
return word.split('').sort().join('');
})
Everytime you push to allSubSets, the length increases, and thus, your loop never ends. A declarative loop runs on the range of the initial loop. See below for a fix based on your code:
var powerSet = function(str) {
let allSubsets = [''];
for (let i = 0; i < str.length; i++) {
allSubsets.forEach( (_char, j) => { // declarative loop here
allSubsets.push(sortLetters(str[i] + allSubsets[j]));
})
}
return allSubsets;
};
var sortLetters = (word => {
return word.split('').sort().join('');
})
From MDN web docs:
The range of elements processed by forEach() is set before the first invocation of callback. Elements which are appended to the array after the call to forEach() begins will not be visited by callback. If existing elements of the array are changed or deleted, their value as passed to callback will be the value at the time forEach() visits them; elements that are deleted before being visited are not visited. If elements that are already visited are removed (e.g. using shift()) during the iteration, later elements will be skipped. (See this example, below.)
See the fourth paragraph under descriptions: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach#Description
I have two arrays. First one which comes from response is divided by pagination. When i remove items from second array, they should be placed back sorted by id in first array, instead they go to bottom of array and i have to scroll down to find certain element. This is my code for pushing elements from array vm.feeds to vm.rationList:
function addAll() {
var mList = JSON.parse(JSON.stringify(vm.feeds))
for (var i = 0; i < mList.length; i++) {
mList[i].is_selected = false;
vm.rationList.push(mList[i]);
}
vm.feeds = [];
vm.rationListSafe = vm.rationList;
if(vm.feeds.length == 0){
vm.currentPageMaster++;
vm.isPage = true;
vm.disableScroll = true;
getFeedsByTeam(vm.selectedTeam);
}
}
Second part is how i remove elements from array vm.rationList and push them back to first array - vm.feeds:
function removeAll() {
for (var i = 0; i < vm.rationList.length; i++) {
vm.feeds.push(vm.rationList[i])
}
vm.rationList = []
}
In removeAll() i have to add additional check which will sort them by ID on push. Any idea for this?
The Array.push method add item to the end of your list.
To put an element at a given position in an array, you may prefer using Array.splice.
First argument is the index, second is the number of items to delete (in your case, 0), and a third argument would be the item to add at the given index.
With that, you can replace the push in removeAll by
vm.feeds.splice(correctIndex, 0, vm.rationList[i]);
Question is : what is correctIndex ?
Well, for that, there might be many solutions depending on your architecture, but a simple one could be to loop on vm.feeds to find the first item with an id that is not lower than the one you want to add:
var correctIndex = 0;
for(var item of vm.feeds) {
if (item.id >= vm.rationList[i].id) {break;}
else {correctIndex++;}
}
vm.feeds.sort(function(a, b) {
return parseFloat(a.id) - parseFloat(b.id);
});
This is the solution I found and it works
Basically i have to create a quiz with 3category. each with 5questions.
I would have to push the selected category-questions into this new array from the array with all the questions. I am unable to do so.
pushSelectedQuestion() {
for (var i = 0; i < this.getNumberOfQuestion; i++) {
if (usercategory == questionPool[i].category) {
mcqSelected.push(questionPool[i])
return mcqSelected;
}
}
}
usercategory = input from user.
if user chooses category 1.
if (1 == questionPool[1].category) (if it matches the category) then it will be pushed.
This is the part which i cant do
Well, from the information you've provided, there's one main issue here - the return statement is definitely shortcutting the loop - so even if you have everything else right, you'll only ever get the first matching question. The rest will have been cut out by the return statement, which stops the function and returns the value.
pushSelectedQuestion() {
for (var i = 0; i < this.getNumberOfQuestion; i++) {
if (usercategory == questionPool[i].category) {
mcqSelected.push(questionPool[i])
// the below line is causing this loop to end after the first time through the list.
// Remove it and then put a console.log(mcqSelected);
// here instead to see the value during each iteration of the loop.
return mcqSelected;
}
}
}
There are a lot of ways to accomplish what you want to do here though. For example, you could just use the javascript Array.filter method like so
let selectedQuestions = questionPool.filter(question => question.category == userCategory)
Maybe I am not understanding your question correctly, but can't you use nested arrays. If the questions are categorized beforehand that is.
I have a JSON response like this:
var errorLog = "[[\"comp\",\"Please add company name!\"],
[\"zip\",\"Please add zip code!\"],
...
Which I'm deserializing like this:
var log = jQuery.parseJSON(errorLog);
Now I can access elements like this:
log[1][1] > "Please add company name"
Question:
If I have the first value comp, is there a way to directly get the 2nd value by doing:
log[comp][1]
without looping through the whole array.
Thanks for help!
No. Unless the 'value' of the first array (maybe I should say, the first dimension, or the first row), is also it's key. That is, unless it is something like this:
log = {
'comp': 'Please add a company name'
.
.
.
}
Now, log['comp'] or log.comp is legal.
There are two was to do this, but neither avoids a loop. The first is to loop through the array each time you access the items:
var val = '';
for (var i = 0; i < errorLog.length; i++) {
if (errorLog[i][0] === "comp") {
val = errorLog[i][1];
break;
}
}
The other would be to work your array into an object and access it with object notation.
var errors = {};
for (var i = 0; i < errorLog.length; i++) {
errors[errorLog[i][0]] = errorLog[i][1];
}
You could then access the relevant value with errors.comp.
If you're only looking once, the first option is probably better. If you may look more than once, it's probably best to use the second system since (a) you only need to do the loop once, which is more efficient, (b) you don't repeat yourself with the looping code, (c) it's immediately obvious what you're trying to do.
No matter what you are going to loop through the array somehow even it is obscured for you a bit by tools like jQuery.
You could create an object from the array as has been suggested like this:
var objLookup = function(arr, search) {
var o = {}, i, l, first, second;
for (i=0, l=arr.length; i<l; i++) {
first = arr[i][0]; // These variables are for convenience and readability.
second = arr[i][1]; // The function could be rewritten without them.
o[first] = second;
}
return o[search];
}
But the faster solution would be to just loop through the array and return the value as soon as it is found:
var indexLookup = function(arr, search){
var index = -1, i, l;
for (i = 0, l = arr.length; i<l; i++) {
if (arr[i][0] === search) return arr[i][1];
}
return undefined;
}
You could then just use these functions like this in your code so that you don't have to have the looping in the middle of all your code:
var log = [
["comp","Please add company name!"],
["zip","Please add zip code!"]
];
objLookup(log, "zip"); // Please add zip code!
indexLookup(log, "comp"); // Please add company name!
Here is a jsfiddle that shows these in use.
Have you looked at jQuery's grep or inArray method?
See this discussion
Are there any jquery features to query multi-dimensional arrays in a similar fashion to the DOM?