Add unique objects to array of objects in Javascript - javascript

I have arrays of objects that look like this:
const array1 = [{id: 1, name: "John"}, {id: 2, name: "Mary"}]
const array2 = [{id: 1, name: "John"}, {id: 3, name: "Phil"}, {id: 4, name: "Sarah"}]
How can I add unique objects from array2 to array1 so it looks like this:
const array1 = [{id: 1, name: "John"}, {id: 2, name: "Mary"}, {id: 3, name: "Phil"}, {id: 4, name: "Sarah"}]
Lodash implementations are permitted. Thanks a lot.

You can use _.unionBy() function to merge unique objects from arrays.
const array1 = [{id: 1, name: "John"}, {id: 2, name: "Mary"}];
const array2 = [{id: 1, name: "John"}, {id: 3, name: "Phil"}, {id: 4, name: "Sarah"}];
console.log(_.unionBy(array1, array2, 'id'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.js"></script>

Using native array functions you can get the desired result as follows:
Concat both arrays first using .concat()
Use .reduce() to create the resultant object having ids as keys and values as relevant object. If already added an object then skip the others with same ids.
Use Object.values() to get an array of the objects from the resultant object.
Demo:
const array1 = [{id: 1, name: "John"}, {id: 2, name: "Mary"}],
array2 = [{id: 1, name: "John"}, {id: 3, name: "Phil"}, {id: 4, name: "Sarah"}];
const result = Object.values(
array1.concat(array2).reduce((r, c) => (r[c.id] = r[c.id] || c, r), {})
);
console.log(result);
.as-console-wrapper { max-height: 100% !important; top: 0; }

You can also do it in one line via native Map object and reduce:
const arr1 = [{id: 1, name: "John"}, {id: 2, name: "Mary"}]
const arr2 = [{id: 1, name: "John"}, {id: 3, name: "Phil"}, {id: 4, name: "Sarah"}]
const result = [...[...arr1, ...arr2]
.reduce((r, c) => (r.set(c.id, c), r), new Map()).values()]
console.log(result)

Related

How to map through a deeply nested array of objects?

const my_arr = [
{id: 1, arr: [{subId: 1, value: 1}],
{id: 2, arr: [{subId: 2, value: 2}],
{id: 3, arr: [{subId: 3, value: 1}],
]
how do I map over this array my_arr and then map over arr to return an array like so:
[
{subId: 1, value: 1},
{subId: 3, value: 1},
]
basically filtering out only where values are 1 and then returning only that sub object
I've tried doing
my_arr.map((x) => x.map((y) => y.value === 1 ? y : null))
You can try this approach with flatMap and filter
const my_arr = [
{id: 1, arr: [{subId: 1, value: 1}]},
{id: 2, arr: [{subId: 2, value: 2}]},
{id: 3, arr: [{subId: 3, value: 1}]},
]
const result = my_arr.flatMap(item => item.arr).filter(item => item.value === 1)
console.log(result)
Your current approach maps over the outer array my_arr, and then uses an inner map to map over the inner array. Since .map() always returns an array, you'll end up mapping your objects from your outer array to other arrays, which you don't want. You can instead use .flatMap() which will combine/join the returned inner arrays into one array. However, rather than using .map() as your inner method though, you should use .filter() to create an array of objects that have a value of 1, which then gets merged into your resulting outer array created by the .flatMap() method:
const my_arr = [ {id: 1, arr: [{subId: 1, value: 1}]}, {id: 2, arr: [{subId: 2, value: 2}]}, {id: 3, arr: [{subId: 3, value: 1}]}, ];
const res = my_arr.flatMap(({arr}) => arr.filter(({value}) => value === 1));
console.log(res);
Since you are dealing with nested structure, you will have to get little creative.
First you will have to filter the array.
Inside it, you can use .some to check if your condition matches and return matching
Now you have the filtered list but you still need to format your output. You can use .reduce and concat arr of every item
This will be useful if you have multiple items in arr.
const my_arr = [
{id: 1, arr: [{subId: 1, value: 1}] },
{id: 2, arr: [{subId: 2, value: 2}] },
{id: 3, arr: [{subId: 3, value: 1}] },
]
const output = my_arr
.filter(({ arr }) =>
arr.some(({value}) => value === 1)
).reduce((acc, { arr }) => acc.concat(arr), [])
console.log(output)

How can I merge two or more arrays containing several objects into one and increment their IDs?

I have three arrays of objects like so
const arr1 = [{id: 1, name: 'Jay'}, {id: 2, name: 'Kay'}];
const arr2 = [{id: 1, name: 'Pete'}, {id: 2, name: 'Liam'}];
const arr3 = [{id: 1, name: 'Baby'}, {id: 2, name: 'Neeson'}, {id: 3, name: 'Kobe'}];
and I want to merge them into a single array like this
const bigArray = [{id: 1, name: 'Jay'}, {id: 2, name: 'Kay'},{id: 3, name: 'Pete'}, {id: 4, name: 'Liam'}, {id: 5, name: 'Baby'}, {id: 6, name: 'Neeson'}, {id: 7, name: 'Kobe'}];
I know I can spread them into a single array using the spread operator but I also need the IDs incremented when they are joined. How can I achieve that?
Reassign the id based on the index:
const merged = [...arr1, ...arr2, ...arr3];
merged.forEach((el, index) => el.id = index + 1);
Add all the array in a single array and than map over it and change index according to need.
const arr1 = [{id: 1, name: 'Jay'}, {id: 2, name: 'Kay'}];
const arr2 = [{id: 1, name: 'Pete'}, {id: 2, name: 'Liam'}];
const arr3 = [{id: 1, name: 'Baby'}, {id: 2, name: 'Neeson'}, {id: 3, name: 'Kobe'}];
let arr = [...arr1,...arr2,...arr3]
let op = arr.map((ele, index) => ({...ele, id: index+1}) )
console.log(op)
You can combine the arrays to a single array using rest parameters and Array.flat(), and then you can use Array.map() to update the objects with the id generated from the index:
const flatAndInc = (...args) =>
args.flat()
.map((o, idx) => ({
...o,
id: idx + 1
}));
const arr1 = [{id: 1, name: 'Jay'}, {id: 2, name: 'Kay'}];
const arr2 = [{id: 1, name: 'Pete'}, {id: 2, name: 'Liam'}];
const arr3 = [{id: 1, name: 'Baby'}, {id: 2, name: 'Neeson'}, {id: 3, name: 'Kobe'}];
const result = flatAndInc(arr1, arr2, arr3);
console.log(result);
You could map new objects without mutating the given data.
const
arr1 = [{id: 1, name: 'Jay'}, {id: 2, name: 'Kay'}],
arr2 = [{id: 1, name: 'Pete'}, {id: 2, name: 'Liam'}],
arr3 = [{id: 1, name: 'Baby'}, {id: 2, name: 'Neeson'}, {id: 3, name: 'Kobe'}],
result = [arr1, arr2, arr3].reduce(
(id => (r, a) => (a.forEach(({ name }) => r.push({ id: id++, name })), r))(1),
[]
);
console.log(result);
All of the other answers are valid, and are mostly more efficient and easier than mine. However, my answer is one of the easiest to understand.
My code uses Spread Syntax (...) to create the big array, but all that does is combines the arrays. Then, I use a .forEach() loop to loop through the array, and redefine the id. Then I incremented the id variable, so that the id's were in order.
const arr1 = [{id: 1, name: 'Jay'}, {id: 2, name: 'Kay'}];
const arr2 = [{id: 1, name: 'Pete'}, {id: 2, name: 'Liam'}];
const arr3 = [{id: 1, name: 'Baby'}, {id: 2, name: 'Neeson'}, {id: 3, name: 'Kobe'}];
let id = 1;
const bigArray = [...arr1, ...arr2, ...arr3];
bigArray.forEach(e => {
e.id = id;
id++;
});
console.log(bigArray);
You can use Array.from and spread
const arr1 = [{id: 1, name: 'Jay'}, {id: 2, name: 'Kay'}];
const arr2 = [{id: 1, name: 'Pete'}, {id: 2, name: 'Liam'}];
const arr3 = [{id: 1, name: 'Baby'}, {id: 2, name: 'Neeson'}, {id: 3, name: 'Kobe'}];
var result = Array.from([...arr1, ...arr2, ...arr3], ({name}, i)=>{ return {id: i + 1, name} });
console.log(result);
You can use reduce() map() and Spread Syntax.
Pass an array of all the arrays you want to merge to function
Flat that array using spread operator.
Then use reduce() to convert all the arrays to single dimensional array.
At last use map() and set it id property to index + 1
const arr1 = [{id: 1, name: 'Jay'}, {id: 2, name: 'Kay'}];
const arr2 = [{id: 1, name: 'Pete'}, {id: 2, name: 'Liam'}];
const arr3 = [{id: 1, name: 'Baby'}, {id: 2, name: 'Neeson'}, {id: 3, name: 'Kobe'}];
function merge(arrays){
return [...arrays].reduce((ac,a) => [...ac,...a],[]).map((x,i) => ({...x,id:i+1}));
}
console.log(merge([arr1,arr2,arr3]));

Merging of two arrays with conditions without using lodash

I am facing problem to merge the two arrays. I have two arrays of objects first is prev having old values and another with updated values. I would like to have result array with all the objects of prev array with its updated value in array next, and also have objects in next array.
Example:
var prev = [{id: 1, val: 'abc'}, {id: 2, val: 'pqr'}];
var next = [{id: 1, val: 'nextVal'}, {id: 3, val: 'xyz'}];
expected
mergeOutput = [
{id: 1, val: 'nextVal'}, // value is updated
{id: 2, val: 'pqr'},
{id: 3, val: 'xyz'}
]
Note: Array order do not matter.
You can use Map() to merge array.
var prev = [{id: 1, val: 'abc'}, {id: 2, val: 'pqr'}];
var next = [{id: 1, val: 'nextVal'}, {id: 3, val: 'xyz'}];
var hash = new Map();
prev.concat(next).forEach(function(obj) {
hash.set(obj.id, Object.assign(hash.get(obj.id) || {}, obj))
});
var mergedArray = Array.from(hash.values());
console.log(mergedArray);
Source : StackOverflow

Finding a key in an object by using values from an array

I have an array which is dynamically created by selecting items from a list:
[2, 4]
I also have an array of objects:
[{id: 1, name: "Param1"}, {id: 2, name: "Param2"}, {id: 3, name: "Param3"}, {id: 4, name: "Param4"}]
What I need to do is use the values in the first array to match against the ids in the objects in the second array and return those objects.
Help with this would be much appreciated
Thanks for your time
You can use this ES6 code, which turns the first array to a Set to allow fast lookup, and then applies the Array filter method, specifically intended for this purpose:
var select = [2, 4];
var data = [{id: 1, name: "Param1"}, {id: 2, name: "Param2"},
{id: 3, name: "Param3"}, {id: 4, name: "Param4"}]
var selectSet = new Set(select);
var result = data.filter( obj => selectSet.has(obj.id) );
console.log(result);
You can just use for loop as Liam's comment, or you can use the filter method of array like this:
var keys = [2, 4];
var objs = [{id: 1, name: "Param1"}, {id: 2, name: "Param2"}, {id: 3, name: "Param3"}, {id: 4, name: "Param4"}];
function filterById(obj) {
return keys.indexOf(obj.id) != -1;
}
var newArr = objs.filter(filterById);
The newArr is the result you want.

Compare the elements of two arrays by Id and remove the elements from the one array that are not presented in the other

I have two arrays of objects like this:
var arr1 = [{Id: 1, Name: "Test1"}, {Id: 2, Name: "Test2"}, {Id: 3, Name: "Test3"}, {Id: 4, Name: "Test4"}]
var arr2 = [{Id: 1, Name: "Test1"}, {Id: 3, Name: "Test3"}]
I need to compare the elements of the two arrays by Id and remove the elements from arr1 that are not presented in arr2 ( does not have element with that Id). How can I do this ?
var res = arr1.filter(function(o) {
return arr2.some(function(o2) {
return o.Id === o2.Id;
})
});
shim, shim, shim.
You can use a function that accepts any number of arrays, and returns only the items that are present in all of them.
function compare() {
let arr = [...arguments];
return arr.shift().filter( y =>
arr.every( x => x.some( j => j.Id === y.Id) )
)
}
var arr1 = [{Id: 1, Name: "Test1"}, {Id: 2, Name: "Test2"}, {Id: 3, Name: "Test3"}, {Id: 4, Name: "Test4"}];
var arr2 = [{Id: 1, Name: "Test1"}, {Id: 3, Name: "Test3"}, {Id: 30, Name: "Test3"}];
var arr3 = [{Id: 1, Name: "Test1"}, {Id: 6, Name: "Test3"}, {Id: 30, Name: "Test3"}];
var new_arr = compare(arr1, arr2, arr3);
console.log(new_arr);
function compare() {
let arr = [...arguments]
return arr.shift().filter( y =>
arr.every( x => x.some( j => j.Id === y.Id) )
)
}
Making use of a hash (a Set) will give a performance gain:
var arr1 = [{Id: 1, Name: "Test1"}, {Id: 2, Name: "Test2"},
{Id: 3, Name: "Test3"}, {Id: 4, Name: "Test4"}];
var arr2 = [{Id: 1, Name: "Test1"}, {Id: 3, Name: "Test3"}];
arr1 = arr1.filter(function (el) {
return this.has(el.Id);
}, new Set(arr2.map(el => el.Id)));
console.log(arr1);
A new Set is created that gets the Id values from arr2:
"1","3"
That Set is passed as the thisArg to filter, so that within the filter callback it is available as this.

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