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How to remove duplicate objects from arrays based on association records in JavaScript

I have to Arrays one is users and another one assignments and users is multidimensional array like below
users = [
{id: 1, name: 'john'},
{id: 2, name: 'john'},
{
id: 3,
name: 'john',
assignments: [
{id: 1, userId: 3, postId: 2}
]
},
]
assignments = [
{id: 1, userId: 3, postId: 2}
]
the I tried
const usersIDs = new Set(users.map(({ id }) => id))
const combined = [
...users,
...assignments.filter(({ userId }) => !usersIDs.has(userId))
]
I want to remove the object from users where id & users.assignments.postId match with assignments table.
I have tried with several ways that find over Google but not luck.
Whats should I do now? How could I achieve that?
Thanks

Please use the below code to acheive your output
assignments.forEach(asgn => {
if (users.some(user => user.id === asgn.postId)) {
const index = users.findIndex(user => user.id === asgn.postId);
users.splice(index, 1);
}
});
console.log(users);

This should work for you.
const users = [
{ id: 1, name: 'john' },
{ id: 2, name: 'john' },
{
id: 3, name: 'john',
assignments: [
{ id: 1, userId: 3, postId: 2 }
]
},
]
const assignments = [
{ id: 1, userId: 3, postId: 2 }
]
assignments.forEach(assignment => {
const index = users.findIndex(
user => user.assignments ? user.assignments.findIndex(a => a.id === assignment.id && a.userId === assignment.userId && a.postId === assignment.postId) : -1);
if (index > -1) {
users.splice(index, 1);
}
});
console.log(users);

Please try this code hope this will work for you.
users = [
{id: 1, name: 'john'},
{id: 2, name: 'john'},
{id: 3, name: 'john',
assignments: [
{id: 1, userId: 3, postId: 2}
]
},
]
assignments = [
{id: 1, userId: 3, postId: 2}
]
users.forEach(matchValueFunction);
function matchValueFunction(item,index) {
if(item.assignments){
for(var i=0; i< assignments.length; i++){
if(item.assignments[0].id == assignments[i].id && item.assignments[0].postId == assignments[i].postId){
users.splice(index);
}
}
}
}
console.log(users);

How can I remove the name field from a json array?

I have a json array like this:
(3) [{…}, {…}, {…}]
0: {Id: 1, Name: "bask"}
1: {Id: 2, Name: "voll"}
2: {Id: 3, Name: "badminton"}
I want to turn it into something like this:
{1:"bask",2:"voll",3:"badminton"}

You can use reduce to loop through array and build a object of desired key/value pair
let data = [{Id: 1, Name: "bask"},{Id: 2, Name: "voll"},{Id: 3, Name: "badminton"}]
let output = data.reduce((op, {Id, Name}) => {
op[Id] = Name
return op
},{})
console.log(output)

You could take Object.fromEntries with the maped key/value pairs.
var array = [{ Id: 1, Name: "bask" }, { Id: 2, Name: "voll" }, { Id: 3, Name: "badminton" }],
object = Object.fromEntries(array.map(({ Id, Name }) => [Id, Name]));
console.log(object);

You can check out the reduce() function!
let array = [
{Id: 1, Name: "bask"},
{Id: 2, Name: "voll"},
{Id: 3, Name: "badminton"}
];
console.log(_.reduce(array, function(result, obj){
result[obj.Id] = obj.Name;
return result;
}, {}));
You can checkout lodash an awesome library with many other such utilities!

You can do this with reduce():
var a = [
{Id: 1, Name: "bask"},
{Id: 2, Name: "voll"},
{Id: 3, Name: "badminton"}
]
b = a.reduce((acc, item) => {
acc[item.Id] = item.Name;
return acc;
}
console.log(b);

You can do it in different ways, here one of them.
let dataArray = [
{id: 1, name: 'bask'},
{id: 2, name: 'voll'},
{id: 3, name: 'badminton'}
]
let ouputObject = {}
dataArray.map(data => {
ouputObject[`${data.id}`] = data.name
})
console.log(ouputObject)
outputObject will be
Object {
1: "bask",
2: "voll",
3: "badminton"
}

Using Array.reduce() :
var arr = [{
Id: 1,
Name: "bask"
}, {
Id: 2,
Name: "voll"
}, {
Id: 3,
Name: "badminton"
}];
var reduceObj = arr.reduce(function(result, currentElement) {
result[currentElement.Id] = currentElement.Name;
return result;
}, {});
console.log(reduceObj);
Using Array.map() :
var arr = [{
Id: 1,
Name: "bask"
}, {
Id: 2,
Name: "voll"
}, {
Id: 3,
Name: "badminton"
}];
var mapObject = {}
arr.map(obj => {
mapObject[obj.Id] = obj.Name
})
console.log(mapObject);

Why does map function return undefined but console.log logs out?

I want to return matching proprieties of two arrays of objects. But I got undefined from map function.
let fruits1 = [
{id: 1, name: "apple"},
{id: 2, name: "dragon fruit"},
{id: 3, name: "banana"},
{id: 4, name: "kiwi"},
{id: 5, name: "pineapple"},
{id: 6, name: "watermelon"},
{id: 7, name: "pear"},
]
let fruits2 = [
{id: 7, name: "pear"},
{id: 10, name: "avocado"},
{id: 5, name: "pineapple"},
]
fruits1.forEach((fruit1) => {
fruits2.filter((fruit2) => {
return fruit1.name === fruit2.name;
}).map((newFruit) => {
//console.log(newFruit.name);
return newFruit.name;
})
})

What are you looking for is an array intersection:
// Generic helper function that can be used for the three operations:
const operation = (list1, list2, isUnion = false) =>
list1.filter( a => isUnion === list2.some( b => a.name === b.name ) );
// Following functions are to be used:
const inBoth = (list1, list2) => operation(list1, list2, true),
inFirstOnly = operation,
inSecondOnly = (list1, list2) => inFirstOnly(list2, list1);
Usage:
console.log('inBoth:', inBoth(list1, list2));
Working Example:
// Generic helper function that can be used for the three operations:
const operation = (list1, list2, isUnion = false) =>
list1.filter( a => isUnion === list2.some( b => a.name === b.name ) );
// Following functions are to be used:
const inBoth = (list1, list2) => operation(list1, list2, true),
inFirstOnly = operation,
inSecondOnly = (list1, list2) => inFirstOnly(list2, list1);
let fruits1 = [
{id: 1, name: "apple"},
{id: 2, name: "dragon fruit"},
{id: 3, name: "banana"},
{id: 4, name: "kiwi"},
{id: 5, name: "pineapple"},
{id: 6, name: "watermelon"},
{id: 7, name: "pear"},
]
let fruits2 = [
{id: 7, name: "pear"},
{id: 10, name: "avocado"},
{id: 5, name: "pineapple"},
]
console.log('inBoth:', inBoth(fruits1, fruits2));

You could use a Set and filter the names.
const names = ({ name }) => name;
var fruits1 = [{ id: 1, name: "apple" }, { id: 2, name: "dragon fruit" }, { id: 3, name: "banana" }, { id: 4, name: "kiwi" }, { id: 5, name: "pineapple" }, { id: 6, name: "watermelon" }, { id: 7, name: "pear" }],
fruits2 = [{ id: 7, name: "pear" }, { id: 10, name: "avocado" }, { id: 5, name: "pineapple" }],
common = fruits1
.map(names)
.filter(Set.prototype.has, new Set(fruits2.map(names)));
console.log(common);

What you want to do is this:
/* first we filter fruits1 (arbitrary) */
let matchingFruits = fruits1.filter(f1 => {
/* then we filter the frut if it exists in frtuis2 */
return fruits2.find(f2 => f2.name === f1.name)
}).map(fruit => fruit.name) // and now we map if we only want the name strings
If you're not using a polyfill Array.find will not work in IE. The alternative would be using Array.indexOf (thanks for pointing this out #JakobE).
Be aware that Array.forEach return value is undefined and that, in order to actually use the Array.map correctly, one has to consume the returned value somehow or assign it to a variable, as we just did with matchingFruits.

JavaScript Update multiple object properties

I have this code below that finds the index of specific object using findIndex method and Update object's name property. Is there anyway i can update mutiple object's name property? E.g.
var rofl = ["0"];
// Instead of ["0"] how do i update multiple object by putting var rofl = ["1","2","3"];
let myArray = [
{id: 0, name: "Jhon"},
{id: 1, name: "Sara"},
{id: 2, name: "Domnic"},
{id: 3, name: "Bravo"}
],
objIndex = myArray.findIndex((obj => obj.id == rofl));
console.log("Before update: ", myArray[objIndex]) // {id: 0, name: "Jhon"}
myArray[objIndex].name = ("Jerry");
console.log("After update: ", myArray[objIndex]) // {id: 0, name: "Jerry"}

Use forEach instead:
const myArray = [
{id: 0, name: "Jhon"},
{id: 1, name: "Sara"},
{id: 2, name: "Domnic"},
{id: 3, name: "Bravo"}
];
["1","2","3"].forEach(findId =>
myArray.find(({ id }) => id == findId).name = 'Jerry'
);
console.log(myArray);
If the IDs have a chance of not existing in the array, you'll have to add a test for that as well:
const myArray = [
{id: 0, name: "Jhon"},
{id: 1, name: "Sara"},
{id: 2, name: "Domnic"},
{id: 3, name: "Bravo"}
];
["1","2","3", "10"].forEach(findId => {
const foundObj = myArray.find(({ id }) => id == findId);
if (foundObj) foundObj.name = 'Jerry';
});
console.log(myArray);

Use Array.forEach
let myArray = [{id: 0, name: "Jhon"},{id: 1, name: "Sara"},{id: 2, name: "Domnic"},{id: 3, name: "Bravo"}];
let rofl = ["1","2","3"];
myArray.forEach((obj) => {if(rofl.includes(obj.id.toString())) obj.name = 'Jerry'})
console.log(myArray);

Merge two arrays of objects with override on key value

I am trying to merge data from json that comes in array of objects. I was using the underscore solution from here merge two json object based on key value in javascript, but it turns out it doesnt override existing items which I need to do as well now.
The result should be all items of array 1 in the same order, overriden by array 2 where id = id. Items in array 2 that does not exist in array 1 should be pushed to the end of the result.
First array:
[
{id: 8, category: "A"}
{id: 2, category: "D"}
{id: 5, category: "C"}
{id: 9, category: "B"}
]
Second array:
[
{id: 1, category: "X"}
{id: 2, category: "Y"}
]
Expected result:
[
{id: 8, category: "A"}
{id: 2, category: "Y"}
{id: 5, category: "C"}
{id: 9, category: "B"}
{id: 1, category: "X"}
]

Use filter, find and concat
Given that
var arr1 = [
{id: 8, category: "A"},
{id: 2, category: "D"},
{id: 5, category: "C"},
{id: 9, category: "B"}
];
var arr2 = [
{id: 12, category: "X"},
{id: 2, category: "Y"}
];
If the order is not important
var output = arr2.concat(
arr1.filter( s =>
!arr2.find( t => t.id == s.id )
)//end filter
);//end concat
Demo
var arr1 = [{
id: 8,
category: "A"
},
{
id: 2,
category: "D"
},
{
id: 5,
category: "C"
},
{
id: 9,
category: "B"
}
];
var arr2 = [{
id: 12,
category: "X"
},
{
id: 2,
category: "Y"
}
];
var output = arr2.concat(
arr1.filter(s =>
!arr2.find(t => t.id == s.id)
) //end filter
); //end concat
console.log(output);
If the order is important
var output = arr1.map(
s => arr2.find(
t => t.id == s.id ) || s
).concat( //end map of arr1
arr2.filter(
s => !arr1.find( t => t.id == s.id )
) //end filter
);//end concat
Demo
var arr1 = [{
id: 8,
category: "A"
},
{
id: 2,
category: "D"
},
{
id: 5,
category: "C"
},
{
id: 9,
category: "B"
}
];
var arr2 = [{
id: 12,
category: "X"
},
{
id: 2,
category: "Y"
}
];
var output = arr1.map(
s => arr2.find(
t => t.id == s.id) || s
).concat( //end map of arr1
arr2.filter(
s => !arr1.find(t => t.id == s.id)
) //end filter
); //end concat
console.log(output);

You could use a Map as closure and store the index of the result array for this id.
var first = [{ id: 8, category: "A" }, { id: 2, category: "D" }, { id: 5, category: "C" }, { id: 9, category: "B" }],
second = [{ id: 12, category: "X" }, { id: 2, category: "Y" }],
result = [first, second].reduce((m => (r, a) => {
a.forEach(o => {
if (m.has(o.id)) {
r[m.get(o.id)] = o;
return;
}
m.set(o.id, r.push(o) - 1);
});
return r;
})(new Map), []);
console.log(result);

You can set a loop on your secondArray and check each object with id value against object with id of firstArray. If you find a match then simply replace the object else push the object:
var firstArray = [
{id: 8, category: "A"},
{id: 2, category: "D"},
{id: 5, category: "C"},
{id: 9, category: "B"}
];
var secondArray = [
{id: 12, category: "X"},
{id: 2, category: "Y"}
];
secondArray.forEach((obj)=>{
var match = false;
for(var i=0; i<firstArray.length; i++){
if(firstArray[i].id === obj.id){
match = true;
firstArray[i] = obj;
break;
}
}
if(!match){
firstArray.push(obj);
}
});
console.log(firstArray);

You can use a forEach to iterate through second array. For each object with the same id in the first array, update the category otherwise push in the new array.
const first = [{id: 8, category: "A"},{id: 2, category: "D"},{id: 5, category: "C"},{id: 9, category: "B"}],
second = [{id: 12, category: "X"},{id: 2, category: "Y"}],
merged = [...first];
second.forEach(o => {
let obj = first.find(({id,category}) => id === o.id);
obj ? obj.category = o.category : merged.push({...o});
});
console.log(merged);

I think reduce is better
first.reduce((res, item) => res.filter(i => i.id !== item.id).concat(item), second);

Using underscore I managed to come up with this answer my own question. It is probably not the most efficent
const newarr = _.map(arr1, obj1 => {
const r = _.find(arr2, obj2 => {
return obj1[match] === obj2[match]
})
if (typeof r === 'undefined') {
return obj1
} else {
return r
}
})
_.each(arr2, obj => {
if (_.indexOf(arr1, _.findWhere(arr1, {id: obj.id})) === -1) {
newarr.push(obj)
}
})

This should work:
const newArr = second.reduce((res, item) => res.filter(i => i.id !== item.id).concat(item), first);