I am stumped.
I have an array of objects that looks like this:
arr = [{source:someID, target:someID},{source:someID, target:someID},...]
After a certain stage, the array’s length reaches around ~20000. At this point in the running of the code, each object within the array is entirely unique.
I need to go on and add further objects to the array but I don’t want any double ups. In this process, another array is looped over to create new objects when two objects share a similar key value. These new objects are then pushed to the above array. Is there a way to test so that the new objects are pushed to this array only if the above array doesn’t already contain an identical object.
I’m not the most proficient in JS, and still learning. So far, I thought of using a nested loop
let testArr = [{code: num, id:num},{code: num, id:num},{code: num, id:num},…] // object being looped over to create more objects for above arr
let testData = testArr;
let arr = [{{source:someID, target:someID},{source:someID, target:someID},...}] // array being added to
let len = testArr.length;
for (let i = 0; i < len; i++) {
let objectTest = testData.findIndex((e) => e.uniqueID.includes(testArr[i].uniqueID));
if (objectTest !== -1) {
if (testArr[i].id !== testData[objectTest].id) {
let testObj = {
source: testArr[i].id,
target: testData[objectTest].id,
};
for (let a = 0; a < arr.length; a++) {
if (deepEqual(arr[a], testObj) === false) {
const newLink = new Object();
newLink.source = testArr[i].id;
newLink.target = testData[objectTest].id;
arr.push(newLink);
}
}
}
}
}
For the deepEqual function I’ve tried numerous different iterations (most found on here) of functions designed to test if objects/arrays are identical and I don’t think those functions on their own are the trouble.
When running this code, I run out of memory (JavaScript heap out of memory) and the app terminates. Was originally running the browser but moved it to Node. If I increased the max ram node could use to 16gb, the app would still terminate with the code: Fatal JavaScript invalid size error 156627439.
What I’m stuck on is a valid way I can check the array to see if there is an identical object already present and then skipping over this if it is true.
Any pointers would be much appreciated.
The biggest issue I can see is inside this piece of code:
for (let a = 0; a < arr.length; a++) {
if (deepEqual(arr[a], testObj) === false) {
const newLink = new Object();
newLink.source = testArr[i].id;
newLink.target = testData[objectTest].id;
arr.push(newLink);
}
}
You are looping while a < arr.length, but you push in the same array, so the length increases. Moreover, you push an object for every entry if you don't find an equal object.
Let's say the are 10 elements and there isn't a single object as the one you want to check inside: on the first iteration deepEqual returns false and you push the element; repeat this step and you'll push 10 times the same element, and the arr.length is now 20, so there will be 10 more iterations where deepEqual returns true and you don't push a new object.
Now just image the same with 20000 elements.
You should just check if it exists in the array, THEN eventually push it.
Try replacing the above with the following solution:
const doesNotContainEqual = arr.every((obj) => !deepEqual(obj, testObj));
if (doesNotContainEqual) {
const newLink = new Object();
newLink.source = testArr[i].id;
newLink.target = testData[objectTest].id;
arr.push(newLink);
}
Related
I am using this script to remove JSON objects from an array, which both appear within the array and another JSON object:
var stageChildren = stage.sprites;
for (var i = 0; i < stageChildren.length; i++) {
for (var x in mainMenu) {
if (mainMenu[x] === stageChildren[i]) {
console.log(x);
}
}
}
To make this more understandable, lets say I had two objects called: object1 & object2.
Inside object1, there may be the same JSON object which also appears within object2. If that's the case, the object is removed from object1.
While this script works, I think it might have a huge impact on performance. Why? Well, there's about 50 separate objects within stageChildren, and 10 inside mainMenu. The script loops through the first object inside stageChildren, checks if that object is also inside mainMenu (by performing a for loop again), and moves onto the next 49 objects.
Is there a more optimized way of doing this?
var index = 0;
var stageChildren = stage.sprites;
for (var x in mainMenu) {
if (stageChildren.includes(mainMenu[x])) {
const result = stageChildren.includes(mainMenu[x])
var index = stageChildren.indexOf(result);
stageChildren.splice(index, 1);
}
}
I am trying to sort a 2D array of custom objects, inside each inner array, based on one of the properties. This sub-arrays each represent one class, the outer array all the classes in the school. My strategy is as such:
Make a copy of the arry to provide a framework with the correct number of subarrays and indeces
Pass a copy of the sub-array to variable
Iterate over that array (the class) and pull out the last name from the object (which holds a number of other pieces of data on the child) and place it in an array that will be the index
Sort the index
Iterate over the class array, find the position of the last name in the index array, and insert the object into that index into the copied 'school'.
But this is not working. In some instances, one or two objects end up in the wrong place, in other instances it completely out of order. I have tried inspecting my index and comparing it with the 2D array, but the index is correct and I can't figure out why its not working. Here is the code:
var studentsInClass = // I have a function here that returns the 2D array of classes containing custom objects
var sortedStudentsInClass = studentsInClass;
var singleClassHolder = [];
var studentIndex = [];
// each iteration is for a single class
for(var i = 0; i < studentsInClass.length; i ++){
studentIndex = [];
singleClassHolder = studentsInClass[i];
// populate the student reference index
for(var j = 0; j < singleClassHolder.length; j++){
studentIndex.push(singleClassHolder[j].ID);
}
studentIndex.sort();
// iterate through students of single class, placing them in alphabetical order
for(var k = 0; k < singleClassHolder.length; k++){
sortedStudentsInClass[i][studentIndex.indexOf(singleClassHolder[k].ID)] = singleClassHolder[k];
}
}
return sortedStudentsInClass;
}
In case the object is important:
function Child(last, first, id, classroom, serviceDays, eligibility){
this.lastName = last;
this.firstName = first;
this.ID = id;
this.class = classroom;
this.maxServiceDays = serviceDays;
this.eligibility = eligibility;
}
And just a side note, it may seem extraneous having created the new singleClassHolder variable. After I noticed I did that, I removed it and just iterated through the 2D array, but that resulted in even more elements out of place.
Make a copy of the arry
var sortedStudentsInClass = studentsInClass;
This won't make a copy. It only makes one variable reference the other in memory. They both refer to the same array in memory. See related answer here.
The easiest way to fix the code is by declaring sortedStudentsInClass as a new array.
var studentsInClass = get2DArrayOfClasses();
var sortedStudentsInClass = [];
/*...*/
for(var k = 0; k < singleClassHolder.length; k++){
sortedStudentsInClass[i] = sortedStudentsInClass[i] || [];//declare inner array, if not present
sortedStudentsInClass[i][studentIndex.indexOf(singleClassHolder[k].ID)] = singleClassHolder[k];
}
I want to filter a array by keeping the same array without creating a new one.
with Array.filter() :
getFiltersConfig() {
return this.config.filter((topLevelConfig) => topLevelConfig.name !== 'origin')
}
what is the best way to get the same result by filtering by value without returning a new array ?
For completeness, I thought it might make sense to show a mutated array variant.
Below is a snippet with a simple function mutationFilter, this will filter the array directly, notice in this function the loop goes in reverse, this is a technique for deleting items with a mutated array.
Also a couple of tests to show how Array.filter creates a new array, and mutationFilter does not.
Although in most cases creating a new array with Array.filter is normally what you want. One advantage of using a mutated array, is that you can pass the array by reference, without you would need to wrap the array inside another object. Another advantage of course is memory, if your array was huge, inline filtering would take less memory.
let arr = ['a','b','a'];
let ref = arr; //keep reference of original arr
function mutationFilter(arr, cb) {
for (let l = arr.length - 1; l >= 0; l -= 1) {
if (!cb(arr[l])) arr.splice(l, 1);
}
}
const cond = x => x !== 'a';
const filtered = arr.filter(cond);
mutationFilter(arr, cond);
console.log(`ref === array -> ${ref === arr}`);
console.log(arr);
console.log(`ref === filtered -> ${ref === filtered}`);
console.log(filtered);
I want to filter a array by keeping the same array without creating a new one.
what is the best way to get the same result by filtering by value without returning a new array ?
I have an answer for the second criterion, but violates the first. I suspect that you may want to "not create a new one" specifically because you only want to preserve the reference to the array, not because you don't want to create a new array, necessarily (e.g. for memory concerns).
What you could do is create a temp array of what you want
var temp = this.config.filter((topLevelConfig) => topLevelConfig.name !== 'origin')
Then set the length of the original array to 0 and push.apply() the values "in-place"
this.config.length = 0; //clears the array
this.config.push.apply(this.config, temp); //adds what you want to the array of the same reference
You could define you custom method like so:
if(!Array.prototype.filterThis){
Array.prototype.filterThis = function (callBack){
if(typeof callBack !== 'function')
throw new TypeError('Argument must of type <function>');
let t = [...this];
this.length = 0;
for(let e of t) if(callBack(e)) this.push(e);
return this;
}
}
let a = [1,2,3,4,5,5,1,5];
a.filterThis(x=>x!=5);
console.log(a);
Warning: Be very cautious in altering built in prototypes. I would even say unless your making a polyfill don't touch. The errors it can cause can be very subtle and very hard to debug.
Not sure why would you want to do mutation but if you really want to do it, maybe assign it back to itself?
let arr = ['a','b','a'];
arr = arr.filter(x => x !== 'a');
console.log(arr)
Consider:
var main = []
Now I want to generate many (289 to be exact) Arrays to be elements in the main one. Each of these arrays will have be like:
var subobject = {x:"A", y:"B", terrain:"C", note:"D"}
Generating the values are no problem, and I can easily put those values in a already defined subobject = {} and push(), but I can't figure out how to iterate a script each time which creates a new object and then push() into var main.
The naming of the subobject is unimportant, I'm looking for solution inwhich I can pull specific information such as:
main[0].x // get x value of the subarray in 0 location in main
main[5].note// get note value of the subarray in 5 location in main
(would it make a difference if every array had the same name? since I would never access subobject directly (after being pushed into main), but through main[X].YYY or would it have to be via main[X].subarray[Y] ?)
for (var i = 0; i < 289; i++) {
main.push({x: getRandomX(), y: getRandomY(), terrain: getTerrain(), note: ""});
}
as long as you create new objects {} before you push them to the array it is ok.
it doesn't matter if you assign the new object to the same variable (ie subobject)
you access them later like this:
main[0].x // get the value of x of the first element
[x:"A", y:"B", terrain:"C", note:"D"] isn't valid javascript, I think you want an object here:
{x:"A", y:"B", terrain:"C", note:"D"}
And to push each generated value, you can use a for loop
for (var i = 0; i < 9; i++) {
//do something, for example, generate a value
}
Arrays are only numerically indexed.
If you want named keys you have to use objects.
Here's the wrong way to do it.
var main = [],
subobject = {x:"A", y:"B", terrain:"C", note:"D"};
for(var i=0; i<289; i++){
subobject["x"] = Math.random();
subobject["terrain"] = Math.random();
//continue adding values using keys
main.push(subobject);
}
The thing is if you just use the same object your going to access that object every time you iterate it, and you'll replace it's value.
So you should do it like this.
var main = [],
subobject = {};
for(var i=0; i<289; i++){
subobject = {};//new object to make for uniquness
subobject["x"] = Math.random();
subobject["terrain"] = Math.random();
//continue adding values using keys
main.push(subobject);
}
You access members like this.
main[0].x;//value of x at index 0
//next index
main[1].terrain;//value of terrain at index 1
Collisions will only happen if you set the same index twice.
main[2].x = "value";
main[2].x = "replace value by accident";
Unless you want to change the value for some reason.
A different index will always give you a different object if you set a different one each time.
I have an array defined as:
var subjectCache = [];
I then have some code to build it up, which is working ok.
However, if I try to reference the array by an index, e.g.:
var x = subjectCache[0];
or
var x = subjectCache[1];
I get undefined.
Also subjectCache.length is always 0 (zero).
if I try to reference it by its key, e.g.:
var x = subjectCache['12345'];
it works.
Is this normal? Shouldn't I be able to reference it by its index whatever?
I'm using Internet Explorer, if it makes a difference (and it probably does :( )
[Edit]
this is the code I'm using to build the array, although I really don't think it is to blame.
It's a callback from a webservice call. This is working fine and the array is being populated.
var subjectCache = [];
var subjectCacheCount = 0;
function refreshSubjectsCallback(data) {
// update subjects
// loop through retrieved subjects and add to cache
for( i=0; i < data.length; i++ )
{
var subject = data[i];
var subjectid = subject.SubjectId;
subjectCache[subjectid] = subject;
subjectCacheCount += 1;
}
}
[/Edit]
You're probably assigning keys manually instead of using subjectCache.push() to add new elements to the array:
var array = [];
array['foo'] = 'bar';
console.log(array.length); // 0
The length attribute isn't going to reflect those changes the way you'd expect:
> var a = [];
undefined
> a[100] = 2; // The previous `100` entries evaluate to `undefined`
2
> a.length;
101
Instead, use an object:
var object = {};
object['foo'] = 'bar';
for (var key in object) {
var value = object[key];
console.log(value);
}
From your symptoms, it sounds like you are trying to treat the array as an associative array.
In Javascript, arrays work like this:
var a = [];
a[1] = 10;
alert(a.length);
Objects work like this:
var o = {};
o.myProp = true;
o["myOtherProp"] = false;
Arrays only work with numeric keys not strings. Strings assign properties to the object, and aren't counted as part of length nor it's numeric indices.
When building the array, make sure you are assigning to a numeric position within the array.
No, it will not work, because you haven't created arrays but objects.
you will have to access it by its key.
var x = subjectCache['12345'];
If this works and subjectCache.length doesn't, I think you are making an object not an array. You are confused.
Somewhere along the road you lost the array, and the variable subjectCache points to a different kind of object.
If it was an array, it can't have the length zero and contain an item that is reachable using subjectCache['12345']. When you access an item in an array it doesn't make any difference if you use a numeric index or a string representing a number.