i have an array that has one element and i want to use proarray.shift();
var proarray=[];
proarray[0]=1;
//...
proarray.shift();
//...
proarray[i]=5;
but when i do, it stops the program.
does it delete the array?
if it does, what should i do to prevent that? cuz i need that array for later.
and also i tried to use
var proarray=[];
proarray[0]=1;
//...
array.splice(0,1);
//...
proarray[i]=5;
but it didn't work.
what should i do?
From the docs.
The shift method removes the element at the zeroeth index and shifts
the values at consecutive indexes down, then returns the removed
value. If the length property is 0, undefined is returned.
The program is likely stopping because you are accessing an index in the array that no longer exists.
Related
I have a simple array as
arr=[{"name":"sam","value":"1"},{"name":"ram","value":"2"},{"name":"jam","value":"3"},{"name":"dam","value":"4"}]
I need to remove the first index from this array and it should be of below type
[{"name":"sam","value":"1"},{"name":"jam","value":"3"},{"name":"dam","value":"4"}]
I tried splice as below
arr.splice(1,1)
But it is giving response {"name":"ram","value":"2"}
how to get [{"name":"sam","value":"1"},{"name":"jam","value":"3"},{"name":"dam","value":"4"}]
It might be very simple question but Im stuck here from sometime.can someone plz help
I think you taking the returning value of Array.prototype.splice().
Array.prototype.splice() returns an array containing the deleted elements.
The splice() method changes the contents of an array by removing or replacing existing elements and/or adding new elements in place
arr=[{"name":"sam","value":"1"},{"name":"ram","value":"2"},{"name":"jam","value":"3"},{"name":"dam","value":"4"}]
arr.splice(1,1)
console.log(arr);
You can compare the difference methods. Be aware if you need change the array or just get a copy to keep with the original one.
Attention: The first array index is 0, not 1. The index one is the second element of the array
The splice method return the element removed from array. That's the reason why you've got the second element from array in your test
Doc: https://bytearcher.com/articles/how-to-delete-value-from-array/
In your question you got the second index that is 1, in order to get the values that was shown, I'll use the index 1 as well.
//DELETE
arr=[{"name":"sam","value":"1"},{"name":"ram","value":"2"},{"name":"jam","value":"3"},{"name":"dam","value":"4"}]
delete arr[1];
console.log("using delete",arr)
//SPLICE METHOD
arr=[{"name":"sam","value":"1"},{"name":"ram","value":"2"},{"name":"jam","value":"3"},{"name":"dam","value":"4"}]
let firstElement = arr.splice(1,1)
console.log("using splice",arr)
console.log("the method splice return the element removed from array",firstElement )
//FILTER METHOD
arr=[{"name":"sam","value":"1"},{"name":"ram","value":"2"},{"name":"jam","value":"3"},{"name":"dam","value":"4"}]
let copyArr = arr.filter((element, index)=>index !== 1)
console.log("extra: using filter (will return a array copy)",copyArr)
this.arol.filter(x=>x.length!==0
?(this.arol.splice(this.arol.indexOf(x),1))
:!true)
I was trying to change it many different ways, but it still does not delete all elements of the array, it always leaves 1 or 2 behind deleting most of them.... I think the problem is with the condition... We are checking if the length of array elements is not 0 (which are all strings)...
Don't try to splice while filtering - instead, return from the filter callback a truthy or falsey value, depending on whether you want to include the item being iterated over in the new array, and use the resulting array that gets returned from .filter:
this.arol = this.arol.filter(x => x.length !== 0);
^^^^^^^^^^^^
If you want to maintain same outer array reference and mutate original you can splice in a loop if you work from end to start so as not to affect indexing you haven't arrived at yet as you change the array length:
const arr = [[1],[],[2]]
arr.reduceRight((_,c,i) => c.length || !!arr.splice(i,1))
console.log(arr)
The problem is you are trying to splice at the same time you are using filter. Filter does not remove elements from your array, it creates a new array with the filtered data, as described here:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter
You can assign the result to the same array as suggested by CertainPerformance.
If Splice is removed from that code then it will not delete elements. this.arol.splice(this.arol.indexOf(x),1) here it will iterate through every element inside that array and x will be current iteration which will splice from the array as you have written splice method. Remove splice it will work fine.
This question already has answers here:
Deleting array elements in JavaScript - delete vs splice
(29 answers)
Closed 4 years ago.
I couldn't find a question that specifically targets the issue I'm having hence this question is being asked.
I have an array that holds 5 numbers:
var numbers = [0,1,2,3,4];
Once a number is clicked on the frontend (website), the number is removed from the array using the below code:
delete numbers[1];
This removes the correct number but leaves a space where the number was (the space is undefined). I believe this is causing an issue. After a number is removed from the array, I use another function to randomly pick any of the remaining numbers in the array however it sometimes fails. After much thought, I've realized it may be because there are empty spaces in the array after a number is removed and as a result, the code fails to work due to the undefined element.
Is my analogy correct or am I mistaken?
(I have also attempted to use the splice method to remove the number however that then causes an issue with the length of my array because if I later want to remove another number, it removes the wrong one due to the numbers moving around etc).
What you'd want to use is splice
In your specific case, numbers.splice(1,1)
You're correct that delete replaces one of the values in the array with undefined, and does not change the array length. Later on when you randomly choose an element from the array, you can wind up getting that undefined value, because it's still taking up a slot in the array:
var numbers = [0,1,2,3,4];
delete numbers[3];
console.log(numbers)
Instead use splice, which removes the item from the array completely:
var numbers = [0,1,2,3,4];
numbers.splice(3,1) /// remove one element starting at index 3
console.log(numbers)
if I later want to remove another number, it removes the wrong one due to the numbers moving around
You do need to choose one behavior or the other. If you need to preserve indexes as is, then continue to use delete, leaving the undefined values in the array, and rewrite your "choose one at random" function to never pick undefined values:
// start with some undefined values:
var numbers = [0, 1, undefined, undefined, undefined, 5]
var pickRandom = function(numbers) {
// make a copy of the array, removing undefined elements:
var definedValues = numbers.filter(function(item) {
return item !== undefined;
});
if (definedValues.length === 0) {return false}
//choose one at random:
return definedValues[Math.floor(Math.random() * definedValues.length)]
}
// test it:
console.log(pickRandom(numbers));
console.log(pickRandom(numbers));
console.log(pickRandom(numbers));
console.log(pickRandom(numbers));
(...but note that this suggests that a simple array is the wrong data structure to use here; you may be better off with an array of objects each with an explicit ID, so you can reference specific ones as needed without worrying about keeping the array index the same.)
If you mean to actually remove the element from the array, leaving your array with 4 elements, then you can use
numbers.splice(1);
This will remove the element in the index 1 from the array and return the section of the new array.
I am dealing with an array that I want to delete an object from and return the new length of the array. For all other numbers, it works - but for one item, it does not. Not sure how to fix it so that the array length is 0 after the only object is deleted. My code is below:
Here's an example where I had one object in the 'player' array:
function deletecamera(id){
alert('before the splice, player length =' + player.length); //returns 1
delete player.splice((id),1);
i=0;
for (i=0;i<player.length;i++){
player.id=i;
}
alert('after reassigning, player length =' + player.length); // still returns 1?!
refreshlist();
}
the delete keyword doesn't remove the object from the array, it sets its value to undefined, so the size of the array stay the same.
See example here: http://jsfiddle.net/up5XX/
If you want to remove the first element from the array player using .splice, you can do this:
player.splice(0, 1);
yeah, thinking a bit more about this, I bet it will work if you change this line:
delete player.splice((id),1);
to
player.splice((id),1);
some weird codes there.
An array in JS is an object that can hold multiple [elements]. But just like with any other JS object you can add more members to it by just saying myArrayName.someMemberName = something. This will not be 'in' the array as if it was an element. This is even the JS poor mans way for an 'associative array’. This is what you are doing now with the .id = ...
You need to change
player.id = i;
into something like
player[i].id = i;
(or something like it. Don't know what the goal is there. I guess you want to reorder all Id's after deleting one in between.)
futhermore ... change the splice line to just this:
player.splice(id,1);
and remove the extra line with just:
i=0;
But I now realise these all are tips but no solution to your problem.
Can you please add
alert('trying to remove id ' + id);
and confirm that you do at least once try to delete id 0 ?
I'm working on JavaScript and I have this JSON object:
var obj ={"name" : "objName",
"dynamicList" :[]};
and then I add some items to my list like this:
obj.dynamicList["someStringID"] = {"watever"};
It's important that I use a string as indexer for each item on my list (i didn't know this could be done until recently).
My only problem now is that whenever I ask for obj.dynamicList.lenght I get 0, unles I manually set the proper number... I was wondering if there's a better way to add items to my list?
Thanks!!
In Javascript, string index is not really an index. It's actually an attribute of the array object. You could set and get the value with the string index, but it's actually an empty array with some attributes. Not only .length, but also .sort(), .splice(), and other array function would not work. If there is a need to use array functions, I would use number as an index to make it a real item in the array.
If you have to use the string as an index, you couldn't rely on .length function. If there is no need to support IE prior to version 9, the Object.keys as suggested by #strimp099 should work. or you may have to create function to count the number of attributes for example:
function len(obj) {
var attrCount = 0;
for(var k in obj) {
attrCount++;
}
return attrCount;
}
and then call
len(obj.dynamicList);
Use the following the find the length of dynamicList object:
Object.keys(obj.dynamicList).length
To do this "the right way," you will have to make obj.dynamicList an object instead of an array; use {} instead of [] to set the initial value.
How to efficiently count the number of keys/properties of an object in JavaScript?
dynamiclist is an object, the length is not the length property you expect from an array.