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I have data array, which has nested arrays inside (level1arr, leve21arr ...)
const data = [
{
level1arr: [
{
level2arr: [{ id: 1, isValid: true }, { id: 2, isValid: true }, { id: 3, isValid: true }],
},
{
level2arr: [{ id: 4, isValid: true }, { id: 5, isValid: true }, { id: 6, isValid: true }],
},
],
},
{
level1arr: [
{
level2arr: [{ id: 7, isValid: true }, { id: 8, isValid: true }, { id: 9, isValid: true }],
},
{
level2arr: [{ id: 10, isValid: true }, { id: 11, isValid: true }, { id: 12, isValid: true }],
},
],
},
];
I also have another array:
const invalidIds = [2,5]
I want to find elements with apecyfic id and change isValid property to false.
Is it better way than iteratinf over multiple nested arrays, like that:
data.forEach(lvl1 => {
lvl1.level1arr.forEach(lvl2 => {
lvl2.level2arr.forEach(element => {
// further nesting
});
});
})
Such iterating over multiple arrays is not good for performance. What is the best way to handle such case with nested arrays?
If it were nested arrays, you could use Array.prototype.flat(). However, you have a mix of nested objects and arrays. You will have to write a custom "flattener" for this data structure. Check this answer for details: how to convert this nested object into a flat object?
You can use recursion until you reach the level you need. Here's one way to do it.
const data = [{
level1arr: [{
level2arr: [{
id: 1,
isValid: true
}, {
id: 2,
isValid: true
}, {
id: 3,
isValid: true
}],
},
{
level2arr: [{
id: 4,
isValid: true
}, {
id: 5,
isValid: true
}, {
id: 6,
isValid: true
}],
},
],
},
{
level1arr: [{
level2arr: [{
id: 7,
isValid: true
}, {
id: 8,
isValid: true
}, {
id: 9,
isValid: true
}],
},
{
level2arr: [{
id: 10,
isValid: true
}, {
id: 11,
isValid: true
}, {
id: 12,
isValid: true
}],
},
],
},
];
const invalidIds =[2,5]
const findId = (object, key, value) => {
if (Array.isArray(object)) {
for (const obj of object) {
findId(obj, key, value);
}
} else {
if (object.hasOwnProperty(key) && object[key] === value) {
object.isValid = false;
return object
}
for (const k of Object.keys(object)) {
if (typeof object[k] === "object") {
findId(object[k], key, value);
}
}
}
}
invalidIds.forEach(id => findId(data, "id", id))
console.log(data)
I would like to filter an array of objects based on the values in another object. I am trying to map() the array and filter() inside the function so that I am able to get a new array with only the desired (active) fields.
I am trying to get the filter on the Object.entries(), I try to compare the keys and check if the values of the active filters are true, but I am not getting it right.
const records = [
{
id: 1,
name: "first",
date: "05/02"
},
{
id: 2,
name: "second",
date: "06/02"
},
{
id: 3,
name: "third",
date: "07/02"
},
{
id: 4,
name: "fourth",
date: "08/02"
}
];
const active = {
id: true,
name: false,
date: true
};
const result = records.map((record) => {
return Object.entries(record).filter((entry) => {
Object.entries(active).forEach((activeEntry) => {
return activeEntry[1] && activeEntry[0] === entry[0];
});
});
});
console.log(result);
This is the desired outcome
const desiredOutcome = [
{
id: 1,
date: "05/02"
},
{
id: 2,
date: "06/02"
},
{
id: 3,
date: "07/02"
},
{
id: 4,
date: "08/02"
}
];
You can filter over the entries of the object and convert it back to an object with Object.fromEntries.
const records=[{id:1,name:"first",date:"05/02"},{id:2,name:"second",date:"06/02"},{id:3,name:"third",date:"07/02"},{id:4,name:"fourth",date:"08/02"}];
const active = {
id: true,
name: false,
date: true
};
const res = records.map(x =>
Object.fromEntries(
Object.entries(x).filter(([k])=>active[k])));
console.log(res);
Simply filter the keys by the key existing and then use Object.fromEntries to go back to an object
const records = [
{
id: 1,
name: "first",
date: "05/02"
},
{
id: 2,
name: "second",
date: "06/02"
},
{
id: 3,
name: "third",
date: "07/02"
},
{
id: 4,
name: "fourth",
date: "08/02"
}
];
const active = {
id: true,
name: false,
date: true
};
const result = records.map((record) => {
return Object.fromEntries( Object.entries(record).filter(([key,value]) => active[key]));
});
console.log(result);
Example of an object in the accounts array:
const accounts = [
{
id: "5f446f2ecfaf0310387c9603",
picture: "https://api.adorable.io/avatars/75/esther.tucker#zillacon.me",
age: 25,
name: {
first: "Esther",
last: "Tucker",
},
company: "ZILLACON",
email: "esther.tucker#zillacon.me",
registered: "Thursday, May 28, 2015 2:51 PM",
},
Example of an object in the books array:
const books = [
{
id: "5f447132d487bd81da01e25e",
title: "sit eiusmod occaecat eu magna",
genre: "Science",
authorId: 8,
borrows: [
{
id: "5f446f2e2cfa3e1d234679b9",
returned: false,
},
{
id: "5f446f2ed3609b719568a415",
returned: true,
},
{
id: "5f446f2e1c71888e2233621e",
returned: true,
},
{
id: "5f446f2e6059326d9feb9a68",
returned: true,
},
{
id: "5f446f2ede05a0b1e3394d8b",
returned: true,
},
{
id: "5f446f2e4081699cdc6a2735",
returned: true,
},
{
id: "5f446f2e3900dfec59489477",
returned: true,
},
{
id: "5f446f2e6059326d9feb9a68",
returned: true,
},
{
id: "5f446f2e409f8883af2955dd",
returned: true,
},
{
id: "5f446f2e3900dfec59489477",
returned: true,
},
{
id: "5f446f2eae901a82e0259947",
returned: true,
},
{
id: "5f446f2ef2ab5f5a9f60c4f2",
returned: true,
},
{
id: "5f446f2ea6b68cf6f85f6e28",
returned: true,
},
{
id: "5f446f2eed18105706d6ca19",
returned: true,
},
{
id: "5f446f2eae901a82e0259947",
returned: true,
},
{
id: "5f446f2e91c2af00cb74e82b",
returned: true,
},
{
id: "5f446f2e5aa2bb5545a0f8a6",
returned: true,
},
{
id: "5f446f2ea508b6a99c3e42c6",
returned: true,
},
{
id: "5f446f2e50cc2da9cd80efdb",
returned: true,
},
{
id: "5f446f2e0b3e2ff72fc503e7",
returned: true,
},
{
id: "5f446f2e91c2af00cb74e82b",
returned: true,
},
{
id: "5f446f2ef795e593cd3cd19d",
returned: true,
},
{
id: "5f446f2e2f35653fa80bf490",
returned: true,
},
{
id: "5f446f2e7b9cd304fed3a8bc",
returned: true,
},
{
id: "5f446f2ed9aac23c0340aab2",
returned: true,
},
],
},
Example of objects in the authors array:
const authors = [
{
id: 0,
name: {
first: "Lucia",
last: "Moreno",
},
},
{
id: 1,
name: {
first: "Trisha",
last: "Mathis",
},
},
{
id: 2,
name: {
first: "Arnold",
last: "Marks",
},
},
I need to write the function function getBooksPossessedByAccount(account, books, authors) {} that does the following: It returns an array of books and authors that represents all books currently checked out by the given account. Look carefully at the object below, as it's not just the book object; the author object is embedded inside of it.
Output example:
getBooksPossessedByAccount(account, books, authors);
[
{
id: "5f447132320b4bc16f950076",
title: "est voluptate nisi",
genre: "Classics",
authorId: 12,
author: {
id: 12,
name: {
first: "Chrystal",
last: "Lester",
},
},
borrows: [
{
id: "5f446f2e6059326d9feb9a68",
returned: false,
},
...
],
},
]
Here's what I have so far:
function getBooksPossessedByAccount(account, books, authors) {
const accId = account.id;
const result = [];
for (let idxBks = 0; idxBks < books.length; idxBks++) {
if (
books[idxBks].borrows.id === accId &&
books[idxBks].borrows.returned === false
) {
result.push(books[idxBks]);
}
for (let idxAuth = 0; idxAuth < authors.length; idxAuth++) {
let authorIdx = authors[idxAuth];
if (authorIdx.id === result.authorId) {
return [result, { author: authorIdx }];
}
}
}
return result;
}
You need to search all the borrows, not just borrows[0]. You can use the some() method to check all of them.
Since the author information needs to be added as a property to the book object, you shouldn't be pushing it onto the booksOut array.
function getBooksPossessedByAccount(account, books, authors) {
const accId = account.id;
const booksOut = books.filter(
(book) => book.borrows.some(borrow => !borrow.returned && borrow.id === accId)
);
booksOut.forEach(book => book.author = authors.find(author => book.authorID == author.id))
return booksOut;
}
Using some should do the trick..
function getBooksPossessedByAccount(account, books, authors) {
let borrowedBooks=books.filter(book=>
book.some(borrow=>borrow.id===account.id)
)
return borrowedBooks //array of book objects
//return borrowedBooks.map(book=>book.id) //to show array of book ids
}
There is an array of objects
const groups = [
{ id: 0, name: "All", selected: false },
{ id: -1, name: "All", selected: true },
{ id: 1, name: "Group1", selected: false },
{ id: 2, name: "Group2", selected: false },
{ id: 3, name: "Group3", selected: false },
{ id: 4, name: "Group4", selected: true }
];
I want to extract ids from this object with map
groups.map(group => group.id > 0 && group.selected ? group.id:null)
but the result will be
[null,null,4,null...]
actually it should be [4]
I know I can use another function like forEach and push or map and filter but I would solve it with one iteration with map or something else.
Filter the object/s under your criteria and then extract the id/s with a map
const groups = [{
id: 0,
name: "All",
selected: false
},
{
id: -1,
name: "All",
selected: true
},
{
id: 1,
name: "Group1",
selected: false
},
{
id: 2,
name: "Group2",
selected: false
},
{
id: 3,
name: "Group3",
selected: false
},
{
id: 4,
name: "Group4",
selected: true
}
];
const result = groups.filter(x => x.id > 0 && x.selected).map(x => x.id)
console.log(result)
you can use a transducer in this case, so that you will not iterate through the array 2 times.
const groups = [
{ id: 0, name: "All", selected: false },
{ id: -1, name: "All", selected: true },
{ id: 1, name: "Group1", selected: false },
{ id: 2, name: "Group2", selected: false },
{ id: 3, name: "Group3", selected: false },
{ id: 4, name: "Group4", selected: true }
];
const filteredIds = groups.reduce(
(ids, { id, selected }) => (
id > 0 && selected ? [...ids, id] : ids
), []
);
console.log(filteredIds);
The map() method creates a new array with the results of calling a function for every array element and extraction is not possible with this. Either use map() and then discard the array items or use filter().
Better approach would be using filter(). The filter() method creates an array filled with all array elements that pass a test (provided as a function).
let result = groups.filter(x => x.id > 0 && x.selected).map(x => x.id)
You can easily do this in one iteration with transducers.
const getPositiveSelectedIDs = pipe([
filter(and([
gt(get('id'), 0),
get('selected'),
])),
map(get('id')),
])
transform(getPositiveSelectedIDs, [])(groups) // => [4]
In this example, getPositiveSelectedIDs is a transducer we declared using functions pipe, map, and filter. The predicate passed to filter uses functions and, gt, and get to say
only let groups through who have positive ids and who have been selected
then, without creating any intermediate arrays, we get the ids of each group with map and get. getPositiveSelectedIDs behaves as a transducer when we use it in transform. The flow of data starts when we call the transformation transform(getPositiveSelectedIDs, []) with groups.
More on transducers
I wrote a function that when given a list of objects and an
id, returns the same list, but with the corresponding object marked active
(all other objects should not be active).
const list = [
{ id: 1, active: false },
{ id: 2, active: false },
{ id: 3, active: true },
{ id: 4, active: false }
];
function markActive(list, value) {
list.forEach((id) => {
if (id.active = (id.id === value)) {
return true;
} else {
return false;
}
});
}
markActive(list, 2);
console.log(list)
Returns:
[ { id: 1, active: false },
{ id: 2, active: false },
{ id: 3, active: false },
{ id: 4, active: true } ]
It's working like a charm, except when I run "npm run [filename]" I get an error message:
Running Tests for [filename].
------------
[ { id: 1, active: false },
{ id: 2, active: false },
{ id: 3, active: false },
{ id: 4, active: true } ]
markActive
1) Case 1 (Given Sample)
2) Case 2 (String IDs)
0 passing (16ms)
2 failing
1) markActive Case 1 (Given Sample):
AssertionError: expected undefined to deeply equal [ { id: 1,
active: false },
{ id: 2, active: true },
{ id: 3, active: false },
{ id: 4, active: false } ]
at Function.assert.deepEqual
(node_modules/chai/lib/chai/interface/assert.js:216:32)
at Context.it (tests/test_02.js:23:12)
2) markActive Case 2 (String IDs):
AssertionError: expected undefined to deeply equal [ { id: '1',
active: false },
{ id: '2', active: true },
{ id: '3', active: false },
{ id: '4', active: false } ]
at Function.assert.deepEqual
(node_modules/chai/lib/chai/interface/assert.js:216:32)
at Context.it (tests/test_02.js:40:12)
Any idea what I'm doing wrong? Here's the code that sets up the tests:
const chai = require("chai");
const sinon = require("sinon");
const assert = chai.assert;
const markActive = require("../answers/02.js");
describe("markActive", () => {
it("Case 1 (Given Sample)", () => {
var list = [
{ id: 1, active: false },
{ id: 2, active: false },
{ id: 3, active: true },
{ id: 4, active: false }
];
var newList = markActive(list, 2);
var targetList = [
{ id: 1, active: false },
{ id: 2, active: true },
{ id: 3, active: false },
{ id: 4, active: false }
];
assert.deepEqual(newList, targetList);
});
it("Case 2 (String IDs)", () => {
var list = [
{ id: "1", active: false },
{ id: "2", active: false },
{ id: "3", active: true },
{ id: "4", active: false }
];
var newList = markActive(list, "2");
var targetList = [
{ id: "1", active: false },
{ id: "2", active: true },
{ id: "3", active: false },
{ id: "4", active: false }
];
assert.deepEqual(newList, targetList);
});
});
Your function isn't returning anything, so any variables you try to set to the result will be set as undefined.
To fix this, simply add a return statement to the end of your function.
function markActive(list, value) {
list.forEach((id) => {
if (id.active = (id.id === value)) {
return true;
} else {
return false;
}
});
return list; // return the updated list
}
NOTE: It's worth mentioning that because the array is referenced, you're modifying the values in-place. This is why the array you defined outside the function still had updated results even though you weren't logging the returned value. This can have unintended side effects if you were to run the markActive() function several times on the same list. If you want a new list to be returned, look into ways of copying and deep copying arrays in Javascript.