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How to join an n-dimension array with different separators for each level?

Sample input
Array
Here I am showing a 3-dimension array but the actual number of dimensions vary and is known as n.
[
[
[1,2],
[3,4]
],
[
[5,6],
[7,8]
]
]
Separators
It has the same length (n) as the number of dimensions of the array where the i-th element represent the separator of the i-th level of the array.
[',', '_', '-']
Desired output
1-2_3-4,5-6_7-8
What I've tried
It works for a 3-dimension array but not for a 4-dimension one.
I know what is going wrong with my code but I have no idea how to fix it.
Besides, I think there are simpler and/or more efficient methods.
3-dimension (working)
const array = [[[1,2],[3,4]],[[5,6],[7,8]]];
const separators = [',', '_', '-'];
const _separators = separators.reverse();
let i;
function join(array, first = false) {
const next = Array.isArray(array[0]);
let result;
if (next) {
result = array.map(e => {
if (first) { i = 0; }
return join(e);
});
i++;
result = result.join(_separators[i]);
}
else {
result = array.join(_separators[i]);
}
return result;
}
const result = join(array, true);
console.log(result);
4-dimension (not working properly)
const array = [[[[1,2],[3,4]],[[5,6],[7,8]]],[[['A','B'],['C','D']],[['E','F'],['G','H']]]];
const separators = ['|', ',', '_', '-'];
const _separators = separators.reverse();
let i;
function join(array, first = false) {
const next = Array.isArray(array[0]);
let result;
if (next) {
result = array.map(e => {
if (first) { i = 0; }
return join(e);
});
i++;
result = result.join(_separators[i]);
}
else {
result = array.join(_separators[i]);
}
return result;
}
const result = join(array, true);
console.log(result);
// desired output: 1-2_3-4,5-6_7-8|A-B_C-D,E-F_G-H

Something like this with recursion
const join = (array, separators, depth) => {
if (depth < separators.length -1) {
return array.map(el => join(el, separators, depth + 1)).join(separators[depth]);
} else {
return array.join(separators[depth]);
}
};
{
const array = [[[1,2],[3,4]],[[5,6],[7,8]]];
const separators = [',', '_', '-'];
console.log(join(array, separators, 0));
}
{
const array = [[[[1,2],[3,4]],[[5,6],[7,8]]],[[['A','B'],['C','D']],[['E','F'],['G','H']]]];
const separators = ['|', ',', '_', '-'];
console.log(join(array, separators, 0));
}

JS: Is using a dictionary faster than looping through an array?

I'm building some program in Nodejs, which will need to keep track in memory of a large number of users. Also, i will have a function that filters a user by id. The code would look something like this:
const users = [
{
id: 1,
name: 'John',
friends: [3, 6, 8]
},
{
id: 2,
name: 'Mark',
friends: [567, 23]
}
]
function getUserById(userId) {
const user = users.filter(user => user.id === userId);
return user[0];
}
The question is, whether this version is generally faster(each key is user id):
const users = {
1: {
id: 1,
name: 'John',
friends: [3, 6, 8]
},
2: {
id: 2,
name: 'Mark',
friends: [567, 23]
}
}
function getUserById(userId) {
return users[userId];
}
My intuition says that the dictionary is faster. What are the facts?

Key lookup time in objects is not guaranteed. It might also be O(n), but most engines will optimize it towards O(1) if you dynamically look up a key multiple times. Filtering an array is O(n), .find() however is twice faster on average:
return users.find(user => user.id === userId);
Now the only datastructure that guarantees O(log n) lookup are Maps:
const userMap = new Map(users.map(u => [u.id, u]));
console.log(userMap.get("test"));
If you however plan to do that in a very large scale (100k is large), I would rather move that task to a database, as it is heavily optimized for those tasks. MongoDB would be easy to adopt, Redis would be very fast, there are many others out there.

I've written a small script that can be copy pasted to the console and shows the actuall data for this question and varifies in practice the answer of Jonas Wilms.
function random_int_from_range(x, y) {
return (x + Math.floor(Math.random() * (y - x + 1)));
}
function generate_name(length_min, length_max) {
var letters = 'abcdefghijklmnopqrstuvwxyz';
var name_array = [];
for (var i = 0; i <= random_int_from_range(length_min, length_max); i ++) {
name_array.push(letters.charAt(Math.floor(Math.random() * letters.length +1)));
}
return name_array.join('')
}
function generate_friends_array(length_min, length_max, num_users) {
friends_array = [];
for (var i = 0; i < random_int_from_range(length_min, length_max); i++) {
friends_array.push(random_int_from_range(0, num_users - 1))
}
return friends_array
}
function generate_users_dict(num_users) {
var users = {};
for (var i = 0; i < num_users; i++) {
users[i] = {
'id': i,
'name': generate_name(4,6),
'friends': generate_friends_array(0, 20, num_users)
}
}
return users
}
function generate_users_list_from_dict(users_dict) {
var users_list = [];
for (var key in users_dict) {
users_list.push(users_dict[key]);
}
return users_list;
}
function get_diff_in_seconds_from_two_milisecond_values(early_value, late_value) {
return (late_value - early_value) / 1000
}
function get_user_by_id_from_dict(users_dict, user_id) {
return users_dict[user_id]
}
function get_user_by_id_from_list(users_list, user_id) {
const users = users_list.filter(user => user.id === user_id);
return users[0]
}
function get_time_for_retrieval_of_item_from_object(object, object_length) {
var function_names = ['get_user_by_id_from_dict', 'get_user_by_id_from_list'];
var random_id = random_int_from_range(0, object_length - 1);
var function_name = '';
if (Array.isArray(object)) {
function_name = function_names[1];
}
else {
function_name = function_names[0];
}
var time_before_retrieval = new Date().getTime();
window[function_name](object, random_id);
var time_after_retrieval = new Date().getTime();
return get_diff_in_seconds_from_two_milisecond_values(time_before_retrieval,
time_after_retrieval);
}
function test_retrieval_times(number_of_users, tests_num, object_type) {
var users_dict = generate_users_dict(number_of_users);
var users_list = generate_users_list_from_dict(users_dict);
var times_array = [];
var object = '';
if (object_type == 'dict') {
object = users_dict;
}
else {
object = users_list;
}
for (var i = 0; i < tests_num; i++) {
times_array.push(get_time_for_retrieval_of_item_from_object(object,
number_of_users));
}
return times_array;
}
function get_average_retrieval_time(object_type, number_of_users,
numbers_of_retrievals) {
var retrieval_times = test_retrieval_times(number_of_users, numbers_of_retrievals,
object_type);
var sum = 0;
for (var i = 0; i < retrieval_times.length; i++) {
sum += retrieval_times[i];
}
console.log('average retrieval time for ' + object_type + ': ' + sum /
numbers_of_retrievals);
}
var number_of_users = parseInt(prompt("Please enter object size", "1000000"));
var number_of_retrievals = parseInt(prompt("Please enter number of retrievals",
"100"));
get_average_retrieval_time('dict', number_of_users, number_of_retrievals);
get_average_retrieval_time('list', number_of_users, number_of_retrievals);
The results of the tests are printed to the console.

Build multidimensional object from a URL

I like to create a object that looks like this for the following URL:
faq/jamie/hutber/faq.json
faq/jamie/hutber/faq_sales.json
sales/people/faq_refunds.json
{
faq: {
jamie: {
hutber:[
"faq.json",
"faq_sales.json"
]
}
},
sales: {
people: [
faq_refunds.json
]
}
}
I feel confident to be able to build we'll need some kind of recursion... which I am lacking in.
const data = {}
const list = 'faq/jamie/hutber/faq.json'.split('/').reverse();
list.forEach((cur, index) => {
if(cur.includes('.json')){
data[cur];
} else if(poo[cur]) {
data[cur] = {}
}else{
data[cur] = {}
}
});

var a = ["faq/jamie/hutber/faq.json",
"faq/jamie/hutber/faq_sales.json",
"sales/people/faq_refunds.json"]; //your URLs
var jsonObj = {}; //this json object will store your result
function urlToJson(array, index, jsonObj){ //function that implements your logic
if(index == array.length - 2){
jsonObj[ array[index] ] = jsonObj[ array[index] ] || [];
jsonObj[ array[index] ].push(array[index + 1]);
return;
}
jsonObj[ array[index] ] = jsonObj[ array[index] ] || {};
urlToJson(array, index + 1, jsonObj[ array[index] ]);
}
for(var key in a){
var array = a[key].split("/");
urlToJson(array, 0, jsonObj);
}
console.log(jsonObj);

You can do this in a loop. Note that you won't support folders that contain both folders and files in your current format.
Here's an example that loops over all paths and adds object to the tree. It's a bit ugly, but it should help you write your own function.
const paths = [
"faq/jamie/hutber/faq.json",
"faq/jamie/hutber/faq_sales.json",
"sales/people/faq_refunds.json"
];
const makeTree = (paths, tree = {}) =>
paths.reduce(
(tree, path) => {
const parts = path.split("/");
const folders = parts.slice(0, -2);
const container = parts[parts.length - 2];
const file = parts[parts.length - 1];
let loc = tree;
folders.forEach(f => {
loc[f] = loc[f] || {};
loc = loc[f];
});
loc[container] = loc[container] || [];
loc[container].push(file);
return tree;
},
tree
);
console.log(makeTree(paths));

Check all words in 'words' collection from DB and check if any words from the text match with any words

I've got a collection in the database MongoDB called words, which stores all words. They have been extracted via queries on the backend and pushed to the front end.
This has been done in the front end:
this.annotationSub = this.annotationService
.getWordUpdateListener()
.subscribe((thewords: ComplexWord[]) => {
this.thewords = thewords;
this.thewords.map(word => {
if (word.word === this.setWord) {
this.wordIWant = word.word;
}
console.log(word);
});
The console.log(word); on top give these fields =
{word: "Lorem", annotation: "Explain Lorem"},
{word: "Aenean", annotation: "Explain Aenean"},
{word: "Hello", annotation: "Explaining Hello"}
This retrieves all the text:
this.postsService.getPosts();
this.postsSub = this.postsService
.getPostUpdateListener()
.subscribe((posts: Post[]) => {
this.posts = posts;
this.posts.map(post => {
if (post.id === this.id) {
this.postIWant = post.fileText;
}
});
});
On this.postIWant I have got all the text from the post.
Now how do I check if any words have any matches with the text in this.postIWant?
Many thanks in advance

This is the best solution.
Passing in the text to the function:
function complexWordIdentification(text) {
const complexWords = ['Hello', 'World', 'Complex Phrase'];
const results = [];
let match, regexp, result;
for (let i = 0; i < complexWords.length; i++) {
// the complex word we are checking in this iteration
const complexWord = complexWords[i];
regexp = new RegExp(complexWord, 'g');
while ((match = regexp.exec(text)) !== null) {
result = {
begin: (regexp.lastIndex - complexWords[i].length),
end: regexp.lastIndex,
text: complexWord
};
results.push(result);
}
}
return results;
}

Return variable from method in a loop

Something like this
var joined = function(arr) {
var res = [];
for (var i in arr) {
var u = DB.getUser(arr[i].user_id, function(user) {
return user;
});
arr[i].user = u;
res = arr[i];
}
return res;
}
I need to get user variable from DB.getUser scope.

Is just inserted some comments into you code to help understand the async flow:
var joined = function(arr) {
// Timestamp: 0
var res = [];
for (var i in arr) {
// Timestamp: 1
var u = DB.getUser(arr[i].user_id, function(user) {
// Timestamp 4 ... length of arr
// user contains what you are looking for
// but this is not return to u, because we passed that a long time ago
return user;
});
// u is null or undefined, because DB.getUser returns nothing
// is a async function, you need wait for the callback
arr[i].user = u;
// Timestamp: 2 return useless arr
res = arr[i];
}
// Timestamp: 3 again, return a useless array
return res;
}
Edit:
You need to this before you pass everything to the template, e.g.:
var joined = function(arr, doneCallback) {
var res = []
var count = arr.length;
for (var i in arr) {
DB.getUser(arr[i].user_id, function(user) {
count--;
res.push(user);
if (count == 0) {
doneCallback(res);
}
})
}
}
joined(somedata, function(mydata) {
render(template, mydata)
});
Take a look at some flow control libraries. (My favorite async)

var getJoinedAndDoSomeThingWithThem = function(ids) {
var joined = [];
var i = 0;
var getAUser = function () {
DB.getUser(ids[i].user_id, function(user) {
joined.push(user);
i++;
if (i == ids.length -1) {
doSomeThingWithTheResult(joined);
return;
}
getAUser();
});
}
getAUser();
}