I don't get how Immutable JS List size will grown.
As in the example on official doc https://facebook.github.io/immutable-js/docs/#/List/push , pushing something in an immutable js List will automatically grown size.
In my code:
const list: List = List();
list.push(object);
console.log(list, list.size);
My output in consolle is:
(1) object
length: 1
___proto___: Array(0)
undefined
That is really different from the aspected output.
There is no size, if I use length in my code Typescript tell me that it doesn't exist "length" in List.
I use React with Typescript and Immutable.JS
Anybody has an idea of what happens?
Immutability means that operations do not change the original object but instead create a new one.
In your case the push method will return a new list with all the old elements and the new one you just added.
Your code should look something like this.
const list: List = List();
const newList = list.push(object);
console.log(list, list.size);
console.log(newlist, newlist.size);
This should print a size of 0 for the list variable and a size of 1 for the newList variable.
Related
I have been trying to filter an Array by its props and not by its value so my original array would be -
const orignalArray =[
{id: 1, name:"jim", email:"jim#mail.com",age:20},
{id: 1, name:"jom", email:"jom#mail.com",age:30}
]
id like to be able to use (n) amount of filters.
My output array would look ideally look like this
const filterList["id","age"]
const newArray=[{name:"jim", email:"jim#mail.com"},{ name:"jom", email:"jom#mail.com"}]
I have tried to use filter() but cant seem to get it to work.
any help is much appreciated.
In this case you aren't filtering the array rather creating a new one based on the original with derived elements from each. To achieve this you can use the array map function to loop over the array and create a new one with new objects without the desired properties, e.g.:
function removeArrayElementProps(arr, propsToRemove) {
return arr.map((element) => {
// Create a copy of the original element to avoid modifying the original
const newElement = {...element};
// Remove the desired properties from the new element
propsToRemove.forEach((propToRemove) => {
delete newElement[propToRemove];
});
// Returning the modified element in map puts it in thew new arry
return newElement;
});
}
Then you simply call:
const newArr = removeArrayElementProps(orignalArray, ['id','age']);
This loops over the array, creates a copy of each element, and removes the specified properties from the element.
Thank you in advance! I'm new to coding and learning how to deal with Arrays. I am trying to remove random items from an array (deck of cards), and populate a new array (called hand). The problem I always seem to have with arrays is taking the results of one and creating a new function/array/ etc.. Currently, I am outputting 2 separate arrays and I can't seem to push them into one.
let deck = ["dA","dQ","dK","dJ","d10","d09","d08",
"d07","d06","d05","d04","d03","d02","hA","hQ","hK",
"hJ","h10","h09","h08","h07","h06","h05","h04","h03"];
var hand = deck.splice(Math.floor(Math.random()*deck.length),1);
console.log(hand)
var hand = deck.splice(Math.floor(Math.random()*deck.length),1);
console.log(hand);
In your code, just you need to push the value returned from splice method rather than directly assigning it.
By this way every time a new value that gets deleted and will be added to the new array called hand. Hope this helps. :-)
let deck = ["dA","dQ","dK","dJ","d10","d09","d08",
"d07","d06","d05","d04","d03","d02","hA","hQ","hK",
"hJ","h10","h09","h08","h07","h06","h05","h04","h03"];
var hand = [];
const getSelectedCard = () => deck.splice(Math.floor(Math.random()*deck.length),1)
let selectedCard = getSelectedCard();
hand.push(...selectedCard) //or hand.push(selectedCard[0])
console.log(hand);
selectedCard = getSelectedCard();
hand.push(...selectedCard)
console.log(hand);
I am pushing an object into an array but cannot do it?
I'm doing it like this
this.passData = this.tribeForm.value;
var id = {"tribe_id": 1}
this.passData.push(id)
This is the value in the tribeForm
I also tried
var id = {tribe_id: 1}
and
this.passData.splice(0,0, id)
and
this.passData = Array.prototype.slice(id)
and
this.passData.concat(id)
but it all ends up with
TypeError: this.passData.push/splice/concat is not a function
The question is not that clear, But I understood you are manipulating form data, value of form data returns an Object, Not an array. Objects in JavaScript are represented as key-value pairs, (or attribute-value) pairs.
Example :
var object = {
name : "Jhon",
grade : 12,
gpa : 8.12
}
It is just a collection of key-value pairs, push(), concat() and other methods are supported only for Arrays not for Objects. You can achieve whatever you want simply by creating a new key/attribute and assigning the value to it.
this.passData = this.tribeForm.value
this.passData['tribe_id'] = 1
//or, Objects can also contain nested object
this.passData['someKey'] = {'tribe_id' : 1}
You can create an empty array and push objects to it
Example :
var exampleArray = []
exampleArray.push({'tribe_id' : 1})
Now, it works because exampleArray is an Array not JS object.
Thanks for A2A
First, you need to understand the error:
TypeError: this.passData.push/splice/concat is not a function
Push/splice/concat is functions for Array and because of that the console is yelling at you that the passData is not an Array.
Make sure your passData is an Array and you will able to do so.
Using JEXL, I am trying to initialize array and than adding elements into it, however below code gives me 'unsolvable property '0' error.
var abc=[];
abc[0]=5;
1) How can I initialize empty array and keep adding values in it?
2) Can I use it like List, where I do not need to specify size at the time of initialization ?
in JEXL syntax you can initialize objects with new function.
Other option is to add to context arraylist:
This is a working example with jexl2:
JexlEngine jexl = new JexlEngine();
String jexlExp = "var abc=new(\"java.util.ArrayList\", 1);abc[0]=5";
Expression e = jexl.createExpression( jexlExp );
List<Integer> abc = new ArrayList<>(1);
JexlContext jc = new MapContext();
//jc.set("abc", abc ); second option to add arraylist to context
Object o = e.evaluate(jc);
In JEXL, the syntax [] creates a Java array, not a List. As an array, it has a fixed size, so you cannot add values to it. However, JEXL 3.2 has a new syntax for creating an ArrayList literal. Basically, you add ... as the final element.
So in JEXL 3.2, your example could be written as:
var abc=[...];
abc.add(5);
See the JEXL literal syntax reference for more information.
I have an array of todos [Todo1, Todo2, Todo3]
Each object has an attribute, :done_date
I need to find the first instance of the object where :done_date => null
THEN I need to know what index it is todos[N] so I can find the object before todos[N-1]
How can I do that?
You could try going about it in a slightly different way. Making use of Ruby's Enumerable#take_while:
# assuming 'todos' holds your todo objects
todos.take_while { |todo| todo.done_date != nil }.last
This will get all todo objects from todos until it sees a nil done_date, and then grab the last one. You'll have the last todo item before the first nil done_date.
So, if you have
todos = [todo1, todo2, todo3, todo4_with_null_done_date]
the code example above will return todo3.
That said, if you're really looking for something that makes use of the array's indicies, you could try something like this as well:
first_nil_index = todos.find_index { |todo| todo.done_date.nil? }
todos[first_nil_index - 1]