How to remove elements from object of arrays

Question

I use an object of arrays and I want to delete a specific value in 1 of the arrays.

let medici= ["Person1","Person2", "Person3", "Person4", "Person5",  "Person6" ];
let giorni = ["Lun", "Mar", "Mer","Gio","Ven"]; let presenti ={};
for  (let giorno of giorni){ presenti[giorno] = medici; }

I obtain:

Gio: ["Person1", "Person2", "Person3", "Person4", "Person5", "Person6"],
  Lun: ["Person1", "Person2", "Person3", "Person4", "Person5", "Person6"],
  Mar: ["Person1", "Person2", "Person3", "Person4", "Person5", "Person6"],
  Mer: ["Person1", "Person2", "Person3", "Person4", "Person5", "Person6"],
  Ven: ["Person1", "Person2", "Person3", "Person4", "Person5", "Person6"]

Now I want to delete specific value in specific array:

giorno="Ven";
nome="Person1";
presenti[giorno].splice(presenti[giorno].indexOf(nome), 1);

It delete the value in all the arrays!!! Not only in the "Ven" one... How can I delete a single one element in a specific array not affecting the other arrays of the object?

Thx

Does this answer your question? [Copy array by value](https://stackoverflow.com/questions/7486085/copy-array-by-value) — Wyck, Jan 21 '22 at 21:16

score 3 · Answer 1 · answered Jan 21 '22 at 20:58

const medici = ["Person1","Person2", "Person3", "Person4", "Person5",  "Person6" ];
const gironi = ["Lun", "Mar", "Mer","Gio","Ven"];
const presenti = {};

for (const giorno of gironi) {
    presenti[giorno] = [...medici];
}

presenti["Ven"].splice(presenti["Ven"].indexOf("Person1"), 1);

console.log(presenti);

Your problem has to do with memory reference, when you equate two variables you are not creating another identical object but copying the object reference from one variable to another, so if you modify X you change Y, to correct you can create another Array using the spread operator [...medici]

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax

score 1 · Accepted Answer · answered Jan 21 '22 at 22:27

When you build your object all the arrays have the same reference so you will need to slice medici on each object value. Take a look to Copy array by value

Now you can use method.

let medici= ["Person1","Person2", "Person3", "Person4", "Person5",  "Person6" ];
let giorni = ["Lun", "Mar", "Mer","Gio","Ven"]; let presenti ={};
for  (let giorno of giorni){ presenti[giorno] = medici.slice(); }

let giorno="Ven";
let nome="Person1";

presenti[giorno].splice(presenti[giorno].indexOf(nome), 1);
console.log(presenti)

score 0 · Answer 3 · answered Jan 21 '22 at 21:11

let medici= ["Person1","Person2", "Person3", "Person4", "Person5",  "Person6" ];
let giorni = ["Lun", "Mar", "Mer","Gio","Ven"]; let presenti ={};
for  (let giorno of giorni){ presenti[giorno] = medici; }

giorno="Ven";
nome="Person1";

const filteredData = presenti[giorno].filter((p)=>p!==nome)

presenti[giorno] = filteredData

console.log(presenti)

It does so because in JavaScript Array and Objects are known as reference types. [Learn more here].1

To fix your problem you can do this:

giorno="Ven";

nome="Person1";

At first filter out Person1 from the array. const filteredData = presenti[giorno].filter((p)=>p!==nome)

Then replace the Ven object with the updated filteredData

presenti[giorno] = filteredData

How to remove elements from object of arrays

3 Answers3