How to get a new array by removing element in another array by index javascript

Question

split() does mutate the array. filter() really remove all elements with the filtered name in array.

Lets say there are two arrays:

listOfPrices = [15, 30, 10, 20, 10]
declinedItems = [0, 2]

So, I want to create a certain array, in Python I can just use

annaItem = [item for item in listOfPrices]

for item in declinedItems:
   annaItem.remove(listOfPrices[item])

If I print annaItem, the result will be [30, 20, 10]

Here is what I have tried in JS

let annaItem = listOfPrices.map(item => {
    return item
  }) 

  for (let item in declinedItems) {
    console.log(item)
    annaItem = annaItem.filter(e => e !== listOfPrices[declinedItems[item]])
  }
  
  console.log(annaItem)

The result will be [30, 20].

Why js is so hard..? Plzzz help me

Vincent Rouilhac · Accepted Answer · 2022-09-15 15:36:41Z

2

You can use filter, it provides a second argument which is the index so in your case you would do

const listOfPrices = [15, 30, 10, 20, 10];
const declinedItems = [0, 2];

const result = listOfPrices.filter((price, index) => {
  return !declinedItems.includes(index);
});

// -- 
const p = document.getElementById("result");
p.textContent = JSON.stringify(result);

<p id="result"></p>

answered Sep 15, 2022 at 15:36

Vincent Rouilhac

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3 Comments

Kuncung Over a year ago

Wow thanks bro that works, I did not know filter() can take 3 arguments. I have practically 0 amounts of syntax knowledge of javascript, so i dont really understand how does the code after 'return' works.

Vincent Rouilhac Over a year ago

declinedItems = [0, 2] index will takes 0 then 1, 2, 3, 4 and finally 5 ! in javascript means negation which means !true === false .includes(x) is a method that returns true if x is contained in the array it is called on, so declinedItems.includes(index) will return true when we encounter a price at one of the index of the array, but we want to do the opposite of that we want to remove those that are included in the array so we add ! before.

Vincent Rouilhac Over a year ago

If you are totally beginner with Javascript I would highly recommend you taking time to familiarize yourself with some of its concepts with this book eloquentjavascript.net

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