I am trying to work with a multi-dimensional in the following way
function 2darray(mynum) {
var outarray[];
outarray.push(1, 3, 5);
outarray.push(2, 4, 6);
var inarray[];
for (var i = 0; i < outarray.length; i++) {
inarray.push(outarray[i]);
}
// now i want to pass info to another function
getmyarray(inarray[mynum])
}
function getmyarray(access) {
// and access the passed values here, but am i doing the following correctly, and what do i put where the ?'s are..
xassess = access[ ? ][0];
yassess = access[ ? ][1];
}
There are no multi dimensional arrays in Javascript, so what you have is an array of arrays, also known as a jagged array.
Just omit the second index, and you will send the inner array to the function:
getmyarray(inarray[mynum]);
In the function you have a plain array of numbers, so just access it by a single index:
xassess = access[0];
yassess = access[1];
There are no traditional multidimensional arrays in javascript, only arrays of arrays.
// a literal array
var my2dArray = [
[1, 2, 3],
[4, 5, 6]
];
// a "constructed" array
var my2dArray = [];
my2dArray.push([1, 2, 3]);
my2dArray[1] = [4, 5, 6];
my2dArray[2] = [];
my2dArray[2][0] = 7;
Accessing a 2D array is pretty plainforward too; it just works like a 1D array returning another array.
my2dArray[0] == [1, 2, 3];
my2dArray[0][0] == 1;
my2dArray[0][1] == 2;
my2dArray[1][2] == 6;
thanks bart!!
var my2dArray =[
[1, 2, 3],
[4, 5, 6]
];
works great! and when i pass it into a function
getmyarray(my2darray[mynum])
i can access like you would expect!
function getmyarray(mypassedarray)
{ var x=mypassedarray[0];
and console.log(x); is correct!
..now i'm not sure why,but when i try to use the passed values in the google earth plug-in i get
"error: error calling method on npobject" and that error comes on the range part...investigation in progress..
Related
I have an initial array,
I've been trying to change values (orders) by using pop, splice methods inside a for loop and finally I push this array to the container array.
However every time initial array is values are pushed. When I wrote console.log(initial) before push method, I can see initial array has been changed but it is not pushed to the container.
I also tried to slow down the process by using settimeout for push method but this didnt work. It is not slowing down. I guess this code is invoked immediately
I would like to learn what is going on here ? Why I have this kind of problem and what is the solution to get rid of that.
function trial(){
let schedulePattern = [];
let initial = [1,3,4,2];
for(let i = 0; i < 3; i++){
let temp = initial.pop();
initial.splice(1,0,temp);
console.log(initial);
schedulePattern.push(initial);
}
return schedulePattern;
}
**Console.log**
(4) [1, 2, 3, 4]
(4) [1, 4, 2, 3]
(4) [1, 3, 4, 2]
(3) [Array(4), Array(4), Array(4)]
0 : (4) [1, 3, 4, 2]
1 : (4) [1, 3, 4, 2]
2 : (4) [1, 3, 4, 2]
length : 3
When you push initial into schedulePattern, it's going to be a bunch of references to the same Array object. You can push a copy of the array instead if you want to preserve its current contents:
schedulePattern.push(initial.slice(0));
Good answer on reference types versus value types here: https://stackoverflow.com/a/13266769/119549
When you push the array to schedulepattern, you are passing a reference to it.
you have to "clone" the array.
use the slice function.
function trial(){
let schedulePattern = [];
let initial = [1,3,4,2];
for(let i = 0; i < 3; i++){
let temp = initial.pop();
initial.splice(1,0,temp);
console.log(initial);
schedulePattern.push(initial.slice());
}
return schedulePattern;
}
You have to know that arrays are mutable objects. What does it mean? It means what is happening to you, you are copying the reference of the object and modifying it.
const array = [1,2,3]
const copy = array;
copy.push(4);
console.log(array); // [1, 2, 3, 4]
console.log(copy); // [1, 2, 3, 4]
There are a lot of methods in Javascript which provide you the way you are looking for. In other words, create a new array copy to work properly without modify the root.
const array = [1,2,3]
const copy = Array.from(array);
copy.push(4);
console.log(array); // [1, 2, 3]
console.log(copy); // [1, 2, 3, 4]
I encourage you to take a look at Array methods to increase your knowledge to take the best decision about using the different options you have.
Using .slice(), I can deep copy a Javascript Array of primitive types, for example:
var arr = [1,2,3,4];
var newArr = arr.slice();
newArr.push(5);
console.log(arr); // [1,2,3,4]
console.log(newArr); // [1,2,3,4,5]
However, If I add a property to arr like so:
arr.prop1 = 5;
and do the same:
var arr = [1,2,3,4];
arr.prop1 = 8;
arr.prop2 = 9;
var newArr = arr.slice();
newArr.push(5);
console.log(arr); // [1, 2, 3, 4, prop1: 9, prop2: 8]
console.log(newArr); // [1, 2, 3, 4, 5]
The property values do not carry over to newArr
I have considered not using .slice() and looping over the property values of arr instead, assigning them to newArr, using :
for (var key in arr) {
if (arr.hasOwnProperty(key)) {
newArr[key] = arr[key];
}
}
console.log(arr); // [1, 2, 3, 4, prop1: 9, prop2: 8]
console.log(newArr); // [1, 2, 3, 4, 5, prop1: 9, prop2: 8]
Is this going to be the quickest way to deep copy these arrays with properties? Is there in easier or cleaner way I can do this using .slice() or another array method? I am doing this operation tens of thousands of times and want it to be as clean and efficient as possible
You are trying to mix an array and object(to make an array behave like an object).
JavaScript array has numeric indexed items.
JavaScript object has string indexed items.
Arrays have a length property that tells how many items are in the array and is automatically updated when you add or remove items to the array.But ...
var arr = [1,2,3,4], newArr = arr.slice();
arr.prop1 = 7;
console.log(arr.length);
The output is 4, though you would expect it to be 5.But arr.prop1 = 7 does not actually add to the array.Setting a string parameter adds to the underlying object.
The length property is only modified when you add an item to the array, not the underlying object.The expression newArr = arr.slice() assigns a new array to newArr, so it remains an array and behaves like a pure array.
The property values do not carry over to newArr
If you still want to proceed using mixed numeric/string indexed sequences, cloning them, try using Object.assign() function. This should be the easiest way for your case:
The Object.assign() method is used to copy the values of all
enumerable own properties from one or more source objects to a target
object.
console.log(Object.assign(newArr, arr));
The output:
[1, 2, 3, 4, prop1: 7]
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign
How about using Object.create(proto)
var arr = [1,2,3,4];
arr.prop1 = 8;
arr.prop2 = 9;
var newArr = Object.create(arr);
newArr.prop1 = 12;
console.log(arr.prop1) // 8
console.log(newArr.prop1) // 12
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/create
Instructions:
Write a function called getAllElementsButLast.
Given an array, getAllElementsButLast returns an array with all the elements but the last.
Below is my code that will not pass the requirements for the question. I am not sure why this is not correct even though I am getting back all the elements besides the last.
var arr = [1, 2, 3, 4]
function getAllElementsButLast(array) {
return arr.splice(0, arr.length - 1)
}
getAllElementsButLast(arr) // [1, 2, 3]
I think the reason why it's not accepted is because with splice() you change the input array. And that's not what you want. Instead use slice(). This method doesn't change the input array.
var arr = [1, 2, 3, 4]
function getAllElementsButLast(array) {
var newArr = array.slice(0, array.length - 1);
return newArr;
}
var r = getAllElementsButLast(arr);
console.log(r);
console.log(arr);
This question already has answers here:
Get all non-unique values (i.e.: duplicate/more than one occurrence) in an array
(97 answers)
Closed 6 years ago.
There is a javascript array
var arr = [0, 1, 2, 2, 3, 3, 5];
I want to choose elements that repeats twice. In this case its 2 and 3. and i want attach them into a variable.
var a = 2, b = 3;
As far as i know there is no built-in function to do that job. How can i do that. Thanks.
You can use filter to get the values that occur twice.
var arr = [0, 1, 2, 2, 3, 3, 5];
var dups = arr.filter ( (v,i,a) => a.indexOf(v) < i );
console.log(dups);
In comments you stated you would only have doubles, but no values that occur more than twice. Note that the above would return a value more than once, if the latter would be the case.
This returns the values in an array, which is how you should work. To put them in separate values can be done as follows:
var [a, b, ...others] = dups;
...but you would have to know how many variables to reserve for that, and it does not make your further program any easier. JavaScript has many nice functions (methods) for arrays, so you should in fact leave them in an array.
There is no built in function to do that indeed.
You will have to loop thought the array and keeping track of the number of occurrences of the elements, while building a response array.
You could filter a sorted array.
var arr = [0, 1, 2, 2, 3, 3, 5],
repeats = arr.filter(function (a, i, aa) {
return aa[i - 1] === a;
});
console.log(repeats);
Most simple way to do this is the following:
var dups = [];
var arr = [0, 1, 2, 2, 3, 3, 5];
arr.forEach(function (v, i, a){
delete arr[i];
if (arr.indexOf(v) !== -1){
dups.push(v);
}
});
console.log(dups);
It's destructive however.
I know how to compare values in two arrays using 2 for loops however I was looking for something a bit more sophisticated like creating an iterator to iterate through one of the arrays and passing the other array to mapmethod . Is that even possible?
I'm doing a small program for class which takes an array and x arguments and I currently have extracted the values from the arguments.
function dest(arr){
var args =[];
for(var i = 1; i < arguments.length; i++){
args.push(arguments[i]);
}
return args;
}
console.log(dest([1, 2, 3, 4], 4, 4));
Now, how could I do the iterator part to compare the values inside arr and args? Thanks for the help.
The result should be the results that match from both arr and args.
You can use the built in filter method
var arr = [2, 3, 4, 5, 6];
var args = [3, 5, 6, 7];
var result = arr.filter(function(element) {
return args.indexOf(element) > -1;
});
This will filter out all the elements out that are not present in both arrays. The result is a new array that contains only the matching values [3, 5, 6].