I have two arrays list1 and list2 which have objects with some properties; userId is the Id or unique property:
list1 = [
{ userId: 1234, userName: 'XYZ' },
{ userId: 1235, userName: 'ABC' },
{ userId: 1236, userName: 'IJKL' },
{ userId: 1237, userName: 'WXYZ' },
{ userId: 1238, userName: 'LMNO' }
]
list2 = [
{ userId: 1235, userName: 'ABC' },
{ userId: 1236, userName: 'IJKL' },
{ userId: 1252, userName: 'AAAA' }
]
I'm looking for an easy way to execute the following three operations:
list1 operation list2 should return the intersection of elements:
[
{ userId: 1235, userName: 'ABC' },
{ userId: 1236, userName: 'IJKL' }
]
list1 operation list2 should return the list of all elements from list1 which don't occur in list2:
[
{ userId: 1234, userName: 'XYZ' },
{ userId: 1237, userName: 'WXYZ' },
{ userId: 1238, userName: 'LMNO' }
]
list2 operation list1 should return the list of elements from list2 which don't occur in list1:
[
{ userId: 1252, userName: 'AAAA' }
]
You could define three functions inBoth, inFirstOnly, and inSecondOnly which all take two lists as arguments, and return a list as can be understood from the function name. The main logic could be put in a common function operation that all three rely on.
Here are a few implementations for that operation to choose from, for which you can find a snippet further down:
Plain old JavaScript for loops
Arrow functions using filter and some array methods
Optimised lookup with a Set
Plain old for loops
// Generic helper function that can be used for the three operations:
function operation(list1, list2, isUnion) {
var result = [];
for (var i = 0; i < list1.length; i++) {
var item1 = list1[i],
found = false;
for (var j = 0; j < list2.length && !found; j++) {
found = item1.userId === list2[j].userId;
}
if (found === !!isUnion) { // isUnion is coerced to boolean
result.push(item1);
}
}
return result;
}
// Following functions are to be used:
function inBoth(list1, list2) {
return operation(list1, list2, true);
}
function inFirstOnly(list1, list2) {
return operation(list1, list2);
}
function inSecondOnly(list1, list2) {
return inFirstOnly(list2, list1);
}
// Sample data
var list1 = [
{ userId: 1234, userName: 'XYZ' },
{ userId: 1235, userName: 'ABC' },
{ userId: 1236, userName: 'IJKL' },
{ userId: 1237, userName: 'WXYZ' },
{ userId: 1238, userName: 'LMNO' }
];
var list2 = [
{ userId: 1235, userName: 'ABC' },
{ userId: 1236, userName: 'IJKL' },
{ userId: 1252, userName: 'AAAA' }
];
console.log('inBoth:', inBoth(list1, list2));
console.log('inFirstOnly:', inFirstOnly(list1, list2));
console.log('inSecondOnly:', inSecondOnly(list1, list2));
Arrow functions using filter and some array methods
This uses some ES5 and ES6 features:
// 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.userId === b.userId ) );
// Following functions are to be used:
const inBoth = (list1, list2) => operation(list1, list2, true),
inFirstOnly = operation,
inSecondOnly = (list1, list2) => inFirstOnly(list2, list1);
// Sample data
const list1 = [
{ userId: 1234, userName: 'XYZ' },
{ userId: 1235, userName: 'ABC' },
{ userId: 1236, userName: 'IJKL' },
{ userId: 1237, userName: 'WXYZ' },
{ userId: 1238, userName: 'LMNO' }
];
const list2 = [
{ userId: 1235, userName: 'ABC' },
{ userId: 1236, userName: 'IJKL' },
{ userId: 1252, userName: 'AAAA' }
];
console.log('inBoth:', inBoth(list1, list2));
console.log('inFirstOnly:', inFirstOnly(list1, list2));
console.log('inSecondOnly:', inSecondOnly(list1, list2));
Optimising lookup
The above solutions have a O(n²) time complexity because of the nested loop -- some represents a loop as well. So for large arrays you'd better create a (temporary) hash on user-id. This can be done on-the-fly by providing a Set (ES6) as argument to a function that will generate the filter callback function. That function can then perform the look-up in constant time with has:
// Generic helper function that can be used for the three operations:
const operation = (list1, list2, isUnion = false) =>
list1.filter(
(set => a => isUnion === set.has(a.userId))(new Set(list2.map(b => b.userId)))
);
// Following functions are to be used:
const inBoth = (list1, list2) => operation(list1, list2, true),
inFirstOnly = operation,
inSecondOnly = (list1, list2) => inFirstOnly(list2, list1);
// Sample data
const list1 = [
{ userId: 1234, userName: 'XYZ' },
{ userId: 1235, userName: 'ABC' },
{ userId: 1236, userName: 'IJKL' },
{ userId: 1237, userName: 'WXYZ' },
{ userId: 1238, userName: 'LMNO' }
];
const list2 = [
{ userId: 1235, userName: 'ABC' },
{ userId: 1236, userName: 'IJKL' },
{ userId: 1252, userName: 'AAAA' }
];
console.log('inBoth:', inBoth(list1, list2));
console.log('inFirstOnly:', inFirstOnly(list1, list2));
console.log('inSecondOnly:', inSecondOnly(list1, list2));
short answer:
list1.filter(a => list2.some(b => a.userId === b.userId));
list1.filter(a => !list2.some(b => a.userId === b.userId));
list2.filter(a => !list1.some(b => a.userId === b.userId));
longer answer:
The code above will check objects by userId value,
if you need complex compare rules, you can define custom comparator:
comparator = function (a, b) {
return a.userId === b.userId && a.userName === b.userName
};
list1.filter(a => list2.some(b => comparator(a, b)));
list1.filter(a => !list2.some(b => comparator(a, b)));
list2.filter(a => !list1.some(b => comparator(a, b)));
Also there is a way to compare objects by references
WARNING! two objects with same values will be considered different:
o1 = {"userId":1};
o2 = {"userId":2};
o1_copy = {"userId":1};
o1_ref = o1;
[o1].filter(a => [o2].includes(a)).length; // 0
[o1].filter(a => [o1_copy].includes(a)).length; // 0
[o1].filter(a => [o1_ref].includes(a)).length; // 1
Just use filter and some array methods of JS and you can do that.
let arr1 = list1.filter(e => {
return !list2.some(item => item.userId === e.userId);
});
This will return the items that are present in list1 but not in list2. If you are looking for the common items in both lists. Just do this.
let arr1 = list1.filter(e => {
return list2.some(item => item.userId === e.userId); // take the ! out and you're done
});
Use lodash's _.isEqual method. Specifically:
list1.reduce(function(prev, curr){
!list2.some(function(obj){
return _.isEqual(obj, curr)
}) ? prev.push(curr): false;
return prev
}, []);
Above gives you the equivalent of A given !B (in SQL terms, A LEFT OUTER JOIN B). You can move the code around the code to get what you want!
function intersect(first, second) {
return intersectInternal(first, second, function(e){ return e });
}
function unintersect(first, second){
return intersectInternal(first, second, function(e){ return !e });
}
function intersectInternal(first, second, filter) {
var map = {};
first.forEach(function(user) { map[user.userId] = user; });
return second.filter(function(user){ return filter(map[user.userId]); })
}
Here is a functionnal programming solution with underscore/lodash to answer your first question (intersection).
list1 = [ {userId:1234,userName:'XYZ'},
{userId:1235,userName:'ABC'},
{userId:1236,userName:'IJKL'},
{userId:1237,userName:'WXYZ'},
{userId:1238,userName:'LMNO'}
];
list2 = [ {userId:1235,userName:'ABC'},
{userId:1236,userName:'IJKL'},
{userId:1252,userName:'AAAA'}
];
_.reduce(list1, function (memo, item) {
var same = _.findWhere(list2, item);
if (same && _.keys(same).length === _.keys(item).length) {
memo.push(item);
}
return memo
}, []);
I'll let you improve this to answer the other questions ;-)
This is the solution that worked for me.
var intersect = function (arr1, arr2) {
var intersect = [];
_.each(arr1, function (a) {
_.each(arr2, function (b) {
if (compare(a, b))
intersect.push(a);
});
});
return intersect;
};
var unintersect = function (arr1, arr2) {
var unintersect = [];
_.each(arr1, function (a) {
var found = false;
_.each(arr2, function (b) {
if (compare(a, b)) {
found = true;
}
});
if (!found) {
unintersect.push(a);
}
});
return unintersect;
};
function compare(a, b) {
if (a.userId === b.userId)
return true;
else return false;
}
Related
I have this array in my next.js app
arr1
[
{
identifier: "60a17722225f2918c445fd19",
name: "Ben Awad",
_id: "60c94480b8d43c28d0a6eb73
},
{
identifier: "60a455d11fa62a1510b408f8",
name: "dev ed"
_id: "60bf62cede309f1a30fe88ab"
}
]
And i have this another big array
arr2
[
{
name: "Ben Awad",
_id: "60a17722225f2918c445fd19
},
{
name: "dev ed",
_id: "60a455d11fa62a1510b408f8"
},
{
name: "Katlyn",
_id: "60a52500ce96f30c14fdaff9"
},
{
name: "Mike",
_id: "60c95deeb8d43c28d0a6eb74"
},
{
name: "Kassandra",
_id: "60c960ddb8d43c28d0a6eb7a"
}
]
I want a new array who should have all users except for those who have similar ids with arr1
So this is the logic i did (Notice that arr1 and arr2 will change constantly)
Me = arr1
AllUsers = arr2
const LookFriends =
Me &&
AllUsers.filter(({ _id }) => {
return Me.friends.indexOf(_id) === -1;
});
console.log(LookFriends);
The output should be Katlyn, Mike and Kassandra, but the console.log says...
[
{
name: "Ben Awad",
_id: "60a17722225f2918c445fd19
},
{
name: "dev ed",
_id: "60a455d11fa62a1510b408f8"
},
{
name: "Katlyn",
_id: "60a52500ce96f30c14fdaff9"
},
{
name: "Mike",
_id: "60c95deeb8d43c28d0a6eb74"
},
{
name: "Kassandra",
_id: "60c960ddb8d43c28d0a6eb7a"
}
]
I'm really having a hard time trying to filter an array based on another array, what can i do ?
You need to use 'findIndex' in this case, then compare the _id field itself:
const LookFriends =
Me &&
AllUsers.filter(({ _id }) => {
return Me.friends.findIndex(friend => friend._id === _id) === -1;
});
If you use "indexOf", it will compare the entire object to just that _id value.
You can extract the identifiers from the first array and filter the second array if the element doesn't match any id in our object or our Set
// with an object
const ids = {}
arr1.forEach(user => {
ids[user.identifier] = true
})
const filtered = arr2.filter(user => !ids[user._id])
// or with a Set
const ids = new Set(arr1.map(user => user.identifier))
const filtered = arr2.filter(user => !ids.has(user._id))
Please have a try with this code.
Me &&
AllUsers.filter(({ _id }) => {
let bExist = false
Me.friends.map( (friend) => {
if ( friend._id === _id )
bExist = true
})
return bExist
});
Let me know if it works or not.
THE PROBLEM:
I have an array of Objects. And a currentObject, that I currently am viewing. I want to get the value from a Property that comes from the Array of Objects, if 2 other properties match.
Here is the Array, simplified:
ARRAY = [{
id: 1,
metadata: {author: "Company1"}
},
{
id: 2,
metadata: {author: "Company2"}
}
Here is the Object, simplified:
OBJECT = {
name: "Something
templateId: 2
}
So, basically, I want to return, the metdata.author information, if the ARRAY.id, matches the OBJECT.templateId..
Here is the code I wrote..
const getAuthorInfo = (connTemplates: ARRAY[], currentConn: ITEM_OBJECT) => {
connTemplates.find((connTemplate: ARRAY_ITEM_OBJECT) => connTemplate.id === currentConn.templateId);
};
console.log('Author Info:', connection); // This though returns the OBJECT, not the ARRAY_ITEM
Any ideas, on how to make this work? I tried to filter as well, with the same condition, but that returned undefined, when I called it in my ReactComponent.
is this what you need?
const arr = [{
id: 1,
metadata: { author: "Company1" }
},
{
id: 2,
metadata: { author: "Company2" }
}]
const obj = {
name: "Something",
templateId: 2
}
function getAuthorInfo(arr, obj) {
const arrItem = arr.find(item => item.id === obj.templateId)
return arrItem.metadata.author
}
console.log(getAuthorInfo(arr, obj))
You are on the right path:
const result = arr.find(f => f.id == obj.templateId).metadata.author;
const arr = [{
id: 1,
metadata: {author: "Company1"}
},
{
id: 2,
metadata: {author: "Company2"}
}]
const obj = {
name: "Something",
templateId: 2
}
const result = arr.find(f => f.id == obj.templateId);
console.log(result);
So I want to get the object by the id 1 in this object:
let users = {
'users': {
'user1': {
'id': '1',
'name': 'Brandon',
'DOB': '05/04/2000'
},
'user2': {
'id': '2',
'name': 'Jefferson',
'DOB': '05/19/2004'
}
}
}
and I want it to return the entire 'user1' array and log it, does anyone know how I could do this?
I looked all over stackoverflow, and docs, and couldn't find a way to do this. Could I get some help?
There are a few approaches, both of these should roughly achieve what you're looking for:
let users = {
'users': {
'user1': {
'id': '1',
'name': 'Brandon',
'DOB': '05/04/2000'
},
'user2': {
'id': '2',
'name': 'Jefferson',
'DOB': '05/19/2004'
}
}
}
const findUserById = (id) => {
const key = Object.keys(users.users).find(user => users.users[user].id === '1')
return users.users[key]
}
console.log(findUserById('1'))
let users = {
'users': {
'user1': {
'id': '1',
'name': 'Brandon',
'DOB': '05/04/2000'
},
'user2': {
'id': '2',
'name': 'Jefferson',
'DOB': '05/19/2004'
}
}
}
const findUserById = (id) => {
const [key, user] = Object.entries(users.users).find(([key, user]) => user.id === '1');
return user;
}
console.log(findUserById('1'))
While the answer by skovy is right and this is what you should be doing in an actual production setting, I would advise against applying it immediately in your situation.
Why? Your question shows that you first need to learn some basic principles any JavaScript programmer should have, that is:
How to iterate over contents of an object
The simplest method used to iterate over an object's keys is the for .. in loop. When iterating over an object's keys using the for .. in loop, the code inside the curly brackets will be executed once for every key of the object we are iterating.
let users = {
"user1": {
"id": 1
},
"user2": {
"id": 2
}
}
for (let key in users) {
console.log(key);
}
The above code will print:
user1
user2
Proceeding from that, it should be clear how to find the element we want:
let foundUser = null;
for (let key in users) {
if (users[key].id === 1) {
foundUser = users[key];
break;
}
}
// now found user is our user with id === 1 or null, if there was no such user
When not to do that
If you have a complex object which is a descendant of another object and don't want to iterate over inherited properties, you could instead get an array of current object's keys with Object.keys:
let users = {
"user1": {
"id": 1
},
"user2": {
"id": 2
}
}
const keys = Object.keys(users) // now this is an array containing just keys ['user1', 'user2'];
let foundUser = null;
// now you can iterate over the `keys` array using any method you like, e.g. normal for:
for (let i = 0; i < keys.length; i++) {
if (users[keys[i]].id === 1) {
foundUser = users[keys[i]];
break;
}
}
// or alternatively `for of`:
for (for key of keys) {
if (users[key].id === 1) {
foundUser = users[key];
break;
}
}
Other options
You could use Object.values to get an array containing all values of the object:
let users = {
"user1": {
"id": 1
},
"user2": {
"id": 2
}
}
const values = Object.values(users); // values: [{"id":1},{"id":2}]
You can now find the entry you want on your own:
let foundUser = null
for (let i = 0; i < values.length; i++) {
if (values[i].id === 1) {
foundUser = values[i];
break;
}
}
Or using the Array's find method:
let foundUser = values.find(user => user.id === 1);
// now foundUser contains the user with id === 1
Or, shorter and complete version:
let users = {
"user1": {
"id": 1
},
"user2": {
"id": 2
}
}
const foundUser = Object.values(users).find(user => user.id === 1);
// now foundUser is `{ id: 1 }`
Not a big fan of reinventing the wheel. We use object-scan for most of our data processing now. It's very handy when you can just use a tool for that kind of stuff. Just takes a moment to wrap your head around how to use it. Here is how it could answer your questions:
// const objectScan = require('object-scan');
const find = (id, data) => objectScan(['**.id'], {
abort: true,
rtn: 'parent',
filterFn: ({ value }) => value === id
})(data);
const users = { users: { user1: { id: '1', name: 'Brandon', DOB: '05/04/2000' }, user2: { id: '2', name: 'Jefferson', DOB: '05/19/2004' } } };
console.log(find('1', users));
// => { id: '1', name: 'Brandon', DOB: '05/04/2000' }
.as-console-wrapper {max-height: 100% !important; top: 0}
<script src="https://bundle.run/object-scan#13.8.0"></script>
Disclaimer: I'm the author of object-scan
A simple for loop would do it:
let users = {
'users': {
'user1': {
'id': '1',
'name': 'Brandon',
'DOB': '05/04/2000'
},
'user2': {
'id': '2',
'name': 'Jefferson',
'DOB': '05/19/2004'
}
}
}
let desiredUser = {};
Object.keys(users.users).forEach((oneUser) => {
if(users.users[oneUser].id === "1")
desiredUser = users.users[oneUser];
});
console.log(desiredUser);
You can also use reduce for this... as well as if you wanted to return the "entire" object, you could do:
let USER_LIST = {
'users': {
'user1': {
'id': '1',
'name': 'Brandon',
'DOB': '05/04/2000'
},
'user2': {
'id': '2',
'name': 'Jefferson',
'DOB': '05/19/2004'
}
}
}
function findUserById(id){
return Object.entries(USER_LIST.users).reduce((a, [user, userData]) => {
userData.id == id ? a[user] = userData : '';
return a;
}, {});
}
console.log(findUserById(1));
I agree with the Answers. just a short and simple way is to use .find() method
//--data returned-----//
data = [{"Id":22,"Title":"Developer"},{"Id":45,"Title":"Admin"}]
fs.readFile('db.json','utf8', function(err,data){
var obj = JSON.parse(data);
console.log(obj);
var foundItem = obj.find(o=>o.Id==id);
console.log(foundItem);
});
I know this question was answered before multiple times.
but i didn't find any solution that helped me out.
I got an array of objects with a Name property. I only want to get the objects with the same name.
How my Array looks like:
[
{
Name: 'test',
coolProperty: 'yeahCool1'
},
{
Name: 'test1',
coolProperty: 'yeahCool2'
},
{
Name: 'test2',
coolProperty: 'yeahCool3'
},
{
Name: 'test3',
coolProperty: 'yeahCool4'
},
{
Name: 'test',
coolProperty: 'yeahCool5'
}
]
so I only want to get:
[
{
Name: 'test',
coolProperty: 'yeahCool1'
},
{
Name: 'test',
coolProperty: 'yeahCool5'
}
]
I hope someone can help me out :)
For an O(N) solution, first reduce the array into an object that counts the number of occurrences of each name, and then filter the input by the occurrence count being 2:
const arr = [
{
Name: 'test',
coolProperty: 'yeahCool1'
},
{
Name: 'test1',
coolProperty: 'yeahCool2'
},
{
Name: 'test2',
coolProperty: 'yeahCool3'
},
{
Name: 'test3',
coolProperty: 'yeahCool4'
},
{
Name: 'test',
coolProperty: 'yeahCool5'
}
];
const counts = arr.reduce((a, { Name }) => {
a[Name] = (a[Name] || 0) + 1;
return a;
}, {});
console.log(arr.filter(({ Name }) => counts[Name] === 2));
You could use reduce() and filter() method to get the required result.
Using filter() method you need to check if length is greater than 2 then need it will be push in new array inside of reduce() method
DEMO
const arr =[{"Name":"test","coolProperty":"yeahCool1"},{"Name":"test1","coolProperty":"yeahCool2"},{"Name":"test2","coolProperty":"yeahCool3"},{"Name":"test3","coolProperty":"yeahCool4"},{"Name":"test","coolProperty":"yeahCool5"}];
let getCount = (name)=>{
return arr.filter(o => o.Name == name).length;
}
console.log(arr.reduce((r,item) => {
let len = getCount(item.Name);
return r.concat(len>1?item:[]);
}, []));
I see that you have already got an answer. So I thought of adding another way using map.
var counts = {};
var repeats = {};
arr.map(i => {
counts[i['Name']] = (counts[i['Name']] || []);
counts[i['Name']].push(i);
if (counts[i['Name']].length > 1) {
repeats[i['Name']] = counts[i['Name']];
}
});
console.log(repeats);
Not the best solution considering the performance. Just wanted to add an alternative method.
Hope it helps!!
I already searched for a tutorial in Google but couldn't find what I needed.
I have an array like this:
[
{Username:'user1', Balance:'123'},
{Username:'user2', Balance:'213'},
{Username:'user1', Balance:'424'}
]
How to merge Balance when the Username is the same, for example merge Balance Username:'user1'
You can use a combination of higher-level built-in functions like Object.keys, Array#reduce, and Array#map to conditionally combine array entries when certain properties match.
var array = [{
Username: 'user1',
Balance: '123'
}, {
Username: 'user2',
Balance: '213'
}, {
Username: 'user1',
Balance: '424'
}]
var map = array.reduce(function (map, e) {
map[e.Username] = +e.Balance + (map[e.Username] || 0)
return map
}, {})
var result = Object.keys(map).map(function (k) {
return { Username: k, Balance: map[k] }
})
console.log(result)
Edit: OP requested that the answer be flexible enough to handle more than one property. I will leave my original snippet up as well, as in the end I think that one was more elegant.
var array = [{
Username: 'user1',
Balance: '123',
Another: '222'
}, {
Username: 'user2',
Balance: '213',
Another: '111'
}, {
Username: 'user1',
Balance: '424',
Another: '121'
}]
// Add elements to this array if you need to handle more properties
var properties = ['Balance', 'Another']
var map = array.reduce(function (map, e) {
map[e.Username] = properties.map(function (property, i) {
return +e[property] + ((map[e.Username] || [])[i] || 0)
})
return map
}, {})
var result = Object.keys(map).map(function (k) {
return map[k].reduce(function (object, e, i) {
object[properties[i]] = e
return object
}, { Username: k })
})
console.log(result)
You could use a single loop with a hash table for the reference to the objects with the same Username.
var data = [{ Username: 'user1', Balance: '123' }, { Username: 'user2', Balance: '213' }, { Username: 'user1', Balance: '424' }],
grouped = [];
data.forEach(function (hash) {
return function (o) {
if (!hash[o.Username]) {
hash[o.Username] = { Username: o.Username, Balance: 0 };
grouped.push(hash[o.Username]);
}
hash[o.Username].Balance += +o.Balance;
};
}(Object.create(null)));
console.log(grouped);
Here's one more solution, which I find a smidge less magicky than gyre's (but I'm also very interested by his.)
function mergeBalances(x) {
var users = [];
users = x.filter(function(entry) {
if(users[entry.Username]) { return false;}
users[entry.Username] = entry.Username;
return true;
})
.map(function(e) { return e.Username; } );
balances = {};
for(var i=0; i < users.length; i++) {
balances[i] = { Username:users[i]};
balances[i].Balance = x.filter(function(e) { return e.Username==users[i]; })
.reduce(function(total, e) { return total + eval(e.Balance);}, 0);
}
return balances;
}
// just call the function on your array
x = [ {Username:'user1', Balance:'123'}, {Username:'user2', Balance:'213'}, {Username:'user1', Balance:'424'} ]
console.log(mergeBalances(x));