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Compare two arrays of objects and merge some fields

I'm working with Angular and RxJs and I have two arrays of objects. I need to change one specific field of the first array, if the second one has the field with the same value (all of the four fields has different names). I did it with nested loops, but I need to find a better solution, my code is down below
My solution is working, but it's not the best, because arrays can be really large - so the code will work slow. If there's 1000 items in each array, it will be 1000000 iterations - that's why I need to find a better solution. I got advice to use multiple consecutive loops, but I don't really get how to use it here
this.api
.getFirstArray()
.pipe(
mergeMap((firstArray) =>
this._secondApi.getSecondArray().pipe(
map((secondArray) => {
for (const item2 of secondArray) {
for (const item1 of firstArray) {
if (item1.someField === item2.otherField)
item1.someOtherField = item2.anotherField;
}
}
return firstArray;
}),
),
),
)
.subscribe((value) => {
this.gridApi?.setRowData(value);
});
So for example my data is
firstArray: [
{ id: 445; name: 'test' },
{ id: 4355; name: 'test1' },
{ id: 234_234; name: 'test2' },
];
secondArray: [
{ firstName: 'test3'; newId: 445 },
{ firstName: 'test5'; newId: 2 },
{ firstName: 'test6'; newId: 234_234 },
];
And the result should be
result: [{ id: 445; name: 'test3' }, { id: 4355; name: 'test1' }, { id: 234_234; name: 'test6' }];
Note: the ids of the first array objects may be repeated - all of the objects names need to be updated

here is the working example of your problem, may be it will help you.
let firstArray = [
{ id: 445, name: 'test' },
{ id: 4355, name: 'test1' },
{ id: '234_234', name: 'test2' },
];
let secondArray = [
{ firstName: 'test3', newId: 445 },
{ firstName: 'test5', newId: 2 },
{ firstName: 'test6', newId: '234_234' },
];
secondArray.forEach(sec => {
let see = firstArray.findIndex(first => first.id === sec.newId);
if (see > -1) {
firstArray[see].name = sec.firstName
}
})
console.log(firstArray)

You still end up with O(N²) complexity (there are two nested loops that he wants to avoid).
Instead, You can use map
const firstArray = [
{ id: 445, name: 'test' },
{ id: 4355, name: 'test1' },
{ id: '234_234', name: 'test2' },
];
const secondArray = [
{ firstName: 'test3', newId: 445 },
{ firstName: 'test5', newId: 2 },
{ firstName: 'test6', newId: '234_234' },
];
const secondMap = new Map();
secondArray.forEach((item) => {
secondMap.set(item.newId, item.firstName);
});
for (const item of firstArray) {
if (secondMap.has(item.id)) {
item.name = secondMap.get(item.id);
}
}
console.log(firstArray)

How to improve time complexity of this snippet?

I am trying to improve the time complexity and quality of the code snippet below.
I am iterating through one array to check if the element this array exists in the object, should this be true it should return the name matching the element id in the object.
how can I do this without having a nested loop?
Can someone tell me what I can do to make this algo better, please?
Thank you all in advance.
let genres = [28, 12, 878];
data = {
genres: [
{
id: 28,
name: 'Action',
},
{
id: 12,
name: 'Adventure',
},
{
id: 16,
name: 'Animation',
},
{
id: 35,
name: 'Comedy',
},
{
id: 80,
name: 'Crime',
},
{
id: 99,
name: 'Documentary',
},
{
id: 18,
name: 'Drama',
},
{
id: 10751,
name: 'Family',
},
{
id: 14,
name: 'Fantasy',
},
{
id: 36,
name: 'History',
},
{
id: 27,
name: 'Horror',
},
{
id: 10402,
name: 'Music',
},
{
id: 9648,
name: 'Mystery',
},
{
id: 10749,
name: 'Romance',
},
{
id: 878,
name: 'Science Fiction',
},
{
id: 10770,
name: 'TV Movie',
},
{
id: 53,
name: 'Thriller',
},
{
id: 10752,
name: 'War',
},
{
id: 37,
name: 'Western',
},
],
};
const getGenreName = () => {
let result = [];
for (let genre of data.genres) {
//console.log("genre", genre.name)
for (let id of genres) {
//console.log('id',genres[i])
if (id === genre.id) result.push(genre.name);
}
}
console.log(result);
};
getGenreName();

You can use reduce and includes as others have already shown. This will make the code a bit cleaner, but not change the overall runtime complexity. To improve runtime complexity you may need to use a different data structure.
For instance instead of
let genres = [1,2,3,4];
as a simple array, you could use a Set, which has a better lookup performance.
let genres = new Set([1,2,3,4]);
Then you can use this as follows
let result = data.genres
.filter(g => genres.has(g.id))
.map(g => g.name);
and won't need any explict for loops

The simplest improvement would probably be converting genres to a Set https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set
and use the has method to check if each id in the data is a member of the set of chosen genres.
You can also convert the data to a map with the ids as the keys in order to look up by id quickly instead of looping, but that is only faster if the data is reused many times.

JavaScript #reduce in the example outlined below would have O(n) time complexity. This only loops through the array once. We could use filter, and map but it would result in us having to loop through the array twice.
const getGenreName = () => {
const genreSet = new Set(genres);
return data.genres.reduce((accumulator, { id, name }) => {
if (genreSet.has(id)) accumulator.push(name);
return accumulator;
}, []);
};
console.log(getGenreName()); // [ 'Action', 'Adventure', 'Science Fiction' ]
We are initializing the reducer to start with the array [], or an empty array, and then checking to see if the genre property of the object is included in the genres array, if it isn't, return the accumulator, if it is, append it to the end of the accumulator and return it.

You wanted this in one loop, so here it is:
let result = [];
data.genres.forEach(function (e) {
if (genres.includes(e.id)) result.push(e.name);
});
console.log(result);
In case you were wondering about forEach, here's a very good reference: https://www.w3schools.com/jsref/jsref_foreach.asp

The current time complexity is O(MN) where M is the length of data.genres and N is the length of genres.
Time complexity in JavaScript depends on which engine you use, but in most cases you can use a Map to reduce this time complexity to O(max{N,M}):
const getGenreName = () => {
const dataGenresMap = new Map( // O(M)
data.genres.map(({id,...params}) => [id,params]) // O(M)
)
let result = []
for (let id of genres) { // O(N)
if (dataGenresMap.has(id)) result.push(dataGenresMap.get(id).name) // O(1)
}
console.log(result)
}

If you might be doing this more than once then I'd recommend using a Map. By creating a hash map, retrieving genre names per id is much more performant.
let genres = [28, 12, 878];
data = {
genres: [
{
id: 28,
name: 'Action',
},
{
id: 12,
name: 'Adventure',
},
{
id: 16,
name: 'Animation',
},
{
id: 35,
name: 'Comedy',
},
{
id: 80,
name: 'Crime',
},
{
id: 99,
name: 'Documentary',
},
{
id: 18,
name: 'Drama',
},
{
id: 10751,
name: 'Family',
},
{
id: 14,
name: 'Fantasy',
},
{
id: 36,
name: 'History',
},
{
id: 27,
name: 'Horror',
},
{
id: 10402,
name: 'Music',
},
{
id: 9648,
name: 'Mystery',
},
{
id: 10749,
name: 'Romance',
},
{
id: 878,
name: 'Science Fiction',
},
{
id: 10770,
name: 'TV Movie',
},
{
id: 53,
name: 'Thriller',
},
{
id: 10752,
name: 'War',
},
{
id: 37,
name: 'Western',
},
],
};
const genreById = new Map ();
data.genres.forEach(({id, name}) => genreById.set(id, name));
const pushMapValueIfTruthy = map => array => key => {
const val = map.get(key);
if (val) {
array.push(val);
}
};
/** function that takes an array, then id, and pushes corresponding name (if exists) into the array. */
const pushGenreNaneIfExists = pushMapValueIfTruthy(genreById);
const getGenreNames = (ids) => {
result = [];
ids.forEach(pushGenreNaneIfExists(result));
return result;
};
console.log(getGenreNames(genres));

Merge duplicated objects in javascript array with their appearance frequence

i have a javascript array who look like this
[
{ quantity: 1, name: 'Menu sandwichs' },
{ quantity: 1, name: 'Menu sandwichs' },
{ quantity: 1, name: 'Menu sandwichs' },
{ quantity: 1, name: 'Pizza' },
{ quantity: 1, name: 'Piza' }
]
and i want to get this array
[
{ quantity:3, name:'Menu Sandwich' },
{ quantity:2, name:'Pizza' }
]
Could you hel me please ?

Assuming the quantities in the original array may sometimes be something other than 1:
const mergeQuantities = (values) => {
const result = {}
values.forEach(({ quantity, name }) => {
result[name] = result[name] || { name, quantity: 0 }
result[name].quantity += quantity
})
return Object.values(result)
}
This creates a new object where the attribute names are the name from each thing in the array. Then iterates over the list, adding each quantity to the result. Finally, it discards the keys, leaving just the array in the form you want.

Javascript Alphabetised Object Key Sorting

I'm wondering, I have the following data structure:
data = [
{
name: 'Alpha',
},
{
name: 'Alfa',
},
{
name: 'Bravo',
},
{
name: 'Brafo',
},
{
name: 'Charlie',
},
{
name: 'Charly',
},
...
{
name: 'Zulu',
},
{
name: 'Zulo',
},
]
I'm expecting there to be at least one, usually more, key for each letter of the alphabet. However, if there isn't a single data.name I would still like in the below data structure to have an empty domains array [].
I was wondering, how could this be manipulated into the following data structure:
data = {
a: {
domains: [
{
name: 'Alpha',
},
{
name: 'Alfa',
},
],
},
b: {
domains: [
...
]
},
...
z: {
domains: [
...
]
},
};
I have used a few methods, which involved a pre-constructed "alphbetised" key = object array, then filtered each on the first letter of the data.name value...but I was wondering if there was a standard and performant method to acheive this?

Using reduce()
const data = [{name:"Alpha"},{name:"Alfa"},{name:"Bravo"},{name:"Brafo"},{name:"Charlie"},{name:"Charly"},{name:"Zulu"},{name:"Zulo"}]
const res = data.reduce((a, v) => {
// prepare key
let key = v.name.substring(0,1).toLowerCase()
// check key in accumulator
if (!a[key]) {
// assign domain object
a[key] = {domains: []}
}
// push domain array
a[key].domains.push(v)
return a
}, {})
console.log(res)

Here is what you want:
data = [
{
name: 'Alpha',
},
{
name: 'Alfa',
},
{
name: 'Bravo',
},
{
name: 'Brafo',
},
{
name: 'Charlie',
},
{
name: 'Charly',
},
{
name: 'Zulu',
},
{
name: 'Zulo',
},
];
console.log(data.reduce((a, c) => {
const firstLetter = c.name[0].toLowerCase();
if (a[firstLetter]) {
a[firstLetter].domains.push(c);
} else {
a[firstLetter] = { domains: [c] };
}
return a;
}, {}));

How to recursively transform an array of nested objects into array of flat objects?

I have the following array of deeply nested objects:
const data = [
{
name: "foo",
children:[
{
count: 1,
name: "A"
},
{
count: 2,
name: "B"
}
]
},
{
name: "bar",
children: [
{
count: 3,
name: "C",
children: [
{
count: 4,
name: "D"
}
]
}
]
}
]
The way I'd like to transform this would be such as:
const expectedStructure = [
{
count: 1,
name: "A",
label: "foo = A"
},
{
count: 2,
name: "B",
label: "foo = B"
},
{
count: 3,
name: "C",
label: "bar = C"
},
{
count: 4,
name: "D",
label: "bar = D"
}
]
I created recursive function that transforms nested array into array of flat objects.
Here's my code:
function getChildren(array, result=[]) {
array.forEach(({children, ...rest}) => {
result.push(rest);
if(children) {
getChildren(children, result);
}
});
return result;
}
And here's output I get:
[ { name: 'foo' },
{ count: 1, name: 'A' },
{ count: 2, name: 'B' },
{ name: 'bar' },
{ count: 3, name: 'C' },
{ count: 4, name: 'D' } ]
The problem is that I need to add label field to every object in my output array, and I can't find a solution without iterating multiple times through the final array to make desired transformation. How to properly insert label field without hugely augmenting complexity of the function?

Check each iteration whether the current item is a "parent" item, and reassign label if it is.
const data = [{name:"foo",children:[{count:1,name:"A"},{count:2,name:"B"}]},{name:"bar",children:[{count:3,name:"C",children:[{count:4,name:"D"}]}]}];
function getChildren(array, result = [], label = "") {
array.forEach(({ children, name, count }) => {
if (!label || name[1]) {
label = `${name} = `;
}
if (count) {
result.push({ count, name, label: label + name });
}
if (children) {
getChildren(children, result, label);
}
});
return result;
}
const res = getChildren(data);
console.log(res);

You can use a different function for the nested levels, so you can pass the top-level name properties down through all those recursion levels.
function getTopChildren(array, result = []) {
array.forEach(({
name,
children
}) => {
if (children) {
getChildren(children, name, result);
}
});
return result;
}
function getChildren(array, name, result) {
array.forEach(({
children,
...rest
}) => {
rest.label = `${name} = ${rest.name}`;
result.push(rest);
if (children) {
getChildren(children, name, result);
}
});
}
const data = [{
name: "foo",
children: [{
count: 1,
name: "A"
},
{
count: 2,
name: "B"
}
]
},
{
name: "bar",
children: [{
count: 3,
name: "C",
children: [{
count: 4,
name: "D"
}]
}]
}
]
console.log(getTopChildren(data));

You can also do this recursively with flatMap based on whether or not a parent has been passed into the recursive call :
const data = [{
name: "foo",
children: [{
count: 1,
name: "A"
},
{
count: 2,
name: "B"
}
]
},
{
name: "bar",
children: [{
count: 3,
name: "C",
children: [{
count: 4,
name: "D"
}]
}]
}
];
function flatten(arr, parent = null) {
return parent
? arr.flatMap(({name, count, children}) => [
{name, count, label: `${parent} = ${name}`},
...flatten(children || [], parent)
])
: arr.flatMap(({name, children}) => flatten(children || [], name));
}
console.log(flatten(data));

Sometimes it's a little easier to reason about the code and write it clearly using generators. You can yield* from the recursive calls:
const data = [{name: "foo",children:[{count: 1,name: "A"},{ count: 2,name: "B"}]},{name: "bar",children: [{count: 3,name: "C",children: [{count: 4,name: "D"}]}]}]
function* flat(input, n){
if (!input) return
if (Array.isArray(input)) {
for (let item of input)
yield* flat(item, n)
}
let _name = n || input.name
if ('count' in input) {
yield { count:input.count, name:input.name, label:`${_name} = ${input.name}`}
}
yield* flat(input.children, _name)
}
let g = [...flat(data)]
console.log(g)
The function returns a generator, so you need to spread it into a list [...flat(data)] if you want a list or iterate over it if you don't need to store the list.