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What is the best way add all array item in Javascript [duplicate]

This question already has answers here:
Merge/flatten an array of arrays
(84 answers)
Closed 1 year ago.
const arr1 = [
[{ id: 1 }],
[{ id: 2 },{ id: 3 }],
[{ id: 4 }]
];
I want to add all items in this array how can I do this. I want my output as Like:
const arr2 = [
{id:1},
{id:2},
{id:3},
{id:4}
]

Using arr1.flat() will work for your example. If you have an array of even greater depth of nested arrays of objects, you can even use arr1.flat(Infinity) to flatten to a variable depth:
const arr1 = [
{ id: 0 },
[{ id: 1 }],
[{ id: 2 },{ id: 3 }],
[{ id: 4 }]
];
console.log(arr1.flat());

How to sync the indices of two arrays based on a shared value in Javascript? [closed]

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Given two arrays of the same length and identical content, how can one sort an array to be the in same order as the second array, based on a shared property?
Example:
let array1 = [{id: 123, ...}, {id: 456, ...}, {id: 789, ...}] // order always stays the same
let array2 = [{id: 456, ...}, {id: 789, ...}, {id: 123, ...}] // order is always different
How can I sort array1 such that:
array1[0].id is 456 and
array2[0].id is 456

Loop through the first and push to the second by index:
let arr1 = [{id: 123}, {id: 456}, {id: 789}] // order always stays the same
let arr2 = [{id: 456}, {id: 789}, {id: 123}]
arr1.forEach((obj1, idx) => {
arr2[idx] = obj1
})
console.log(arr1, arr2)

Assuming array2 has the objects we care about and array1 specifies the order, map over the ordering array using it to select the objects to be ordered...
let array1 = [{id: 123 }, {id: 456 }, {id: 789, }]
let array2 = [{id: 456, name: '456' }, {id: 789, name: '789' }, {id: 123, name: '123' }]
let array2ElementsSortedByArray1 = array1.map(e => {
return array2.find(e2 => e2.id === e.id)
})
console.log(array2ElementsSortedByArray1)

You can create a hash of the shape {id: index, ...} from array2 and then use this to order the elements of array1. This saves you the cost of find() on each iteration.
let array1 = [{ id: 123, }, { id: 456, }, { id: 789, }] // order always stays the same
let array2 = [{ id: 456, }, { id: 789, }, { id: 123, }]
const
indeces = Object.fromEntries(array2.map(({ id }, i) => [id, i])), // { 456: 0, 789: 1, 123: 2 }
ordered = [];
array1.forEach(o => ordered[indeces[o.id]] = { ...o });
console.log(ordered)

Unique objects from array based on two properties javascript [closed]

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lets say we have an array of objects:
results = [
{id: 1, name: John},
{id: 2, name: Gabo},
{id: 1, name: Anna},
{id: 3, name: Gabo}
{id: 1, name: Jack}, ]
I want function which gets all this objects which has unique id and name and it's value is not in other object.
results = [
{id: 1, name: John}, // unique id-name so we add to array
{id: 2, name: Gabo}, // unique id-name so we add to array
{id: 1, name: Anna}, // name is unique but object with this id already exists in array so we reject
{id: 3, name: Gabo} // id is unique but object with this name already exists in array so we reject
{id: 1, name: Jack}, ] //etc..
results = [
{id: 1, name: John},
{id: 2, name: Gabo},

You can use Set to register and then quickly check for duplicate id or name:
function getUniq(items) {
const ids = new Set();
const names = new Set();
return items.filter((item) => {
if (ids.has(item.id) || names.has(item.name)) {
return false;
}
ids.add(item.id);
names.add(item.name);
return true;
});
}

How to implement complex arrays? [closed]

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For example, when id is equal to 1, an array is ['a', 'b'], and when id is equal to 2, another array is ['c']. The result of these two arrays is [["a","b "],["c"]]
I want the results as follows:
[["a","b"],["c"]]
my code:
var data = [{
id: 1,
name: 'a'
},
{
id: 1,
name: 'b'
},
{
id: 2,
name: 'c'
}
]

Using reduce:
var data = [{
id: 1,
name: 'a'
},
{
id: 1,
name: 'b'
},
{
id: 2,
name: 'c'
}
]
let result = data.reduce((acc, item) => {
return item.id === 1 ? acc[0].push(item.name) : acc[1].push(item.name), acc
},[[], []])
console.log(result)

JavaScript/React - Update a value in array with particular key name from a array of arrays [duplicate]

This question already has answers here:
Find object by id in an array of JavaScript objects
(36 answers)
Closed 5 years ago.
In the below array of arrays I need to update the id value for a particular name.
objArray = [{ name: John, id: 12}, { name: Jake, id: 45}, { name: Jacob, id: 78}];
Ex: If user enters a name and id in text boxes and clicks submit I want to update the id in the array for the particular name.
I can accomplish this using for loops but can you please let me know the most efficient way to do this in Java Script/React?

Use the find function and set the entered name.
Look at this code snippet
let objArray = [{ name: "John", id: 12}, { name: "Jake", id: 45}, { name: "Jacob", id: 78}];
let name = 'Jake'
let newId = 59;
objArray.find((o) => o.name === name).id = newId;
console.log(objArray);
.as-console-wrapper {
max-height: 100% !important
}

You can use findIndex to get the index of the object whose name matches. Then use that index to update the id
var objArray = [{
name: 'John',
id: 12
}, {
name: 'Jake',
id: 45
}, {
name: 'Jacob',
id: 78
}];
function update() {
var getVal = document.getElementById('ip').value.trim();
var getIndex = objArray.findIndex(function(item) {
return item.name.toLowerCase() === getVal.toLowerCase();
})
objArray[getIndex].id= "newId"
console.log(objArray)
}
<input type="text" id="ip">
<button onclick="update()">Update</button>