using javascript filter() with a flag

using javascript filter() with a flag - javascript

I want to return arr2 but want to prompt the user whether there's changes or not by comparing it with arr. with below's approach, I got id of undefined if arr2 have any missing item.
var arr = [{
id: 1,
name: 'something'
}, {
id: 2,
name: 'something2'
}]
var arr2 = [{
id: 1,
name: 'something'
}]
var result = arr.filter(function(obj, i) {
return obj.id == arr2[i].id;
});
document.write(JSON.stringify(result))

The problem in your code is that arr[1] is undefined and you are trying to get id property of undefined. Now what you can do is, get id's in array then get index and check based on that in filter.
var arr = [{
id: 1,
name: 'something'
}, {
id: 2,
name: 'something2'
}]
var arr2 = [{
id: 1,
name: 'something'
}];
var arrIds = arr2.map(function(v) {
return v.id;
});
var result = arr.filter(function(obj) {
var i = arrIds.indexOf(obj.id);
return i > -1 &&
obj.name == arr2[i].name; // check name property here
});
document.write(JSON.stringify(result))

Loop through arr2 in a callback of the .filter to test each item of arr2.
var arr = [{
id: 1,
name: 'something'
}, {
id: 2,
name: 'something2'
}]
var arr2 = [{
id: 1,
name: 'something'
}, {
id: 5,
name: 'something'
}, {
id: 8,
name: 'something'
}];
var isValInArr = function(arr, key, val) {
for (var i = 0, len = arr.length; i < len; i++) {
if (arr[i][key] === val) {
return true;
}
}
return false;
};
var result = arr.filter(function(obj, i) {
return isValInArr(arr2, 'id', obj.id);
});
document.write(JSON.stringify(result))

Related

Set object property in an array true/false, whether the id matches with any id from another array of objects

So first, here's a simple snippet to demonstrate what I mean exactly, and what I have tried.
let array_1 = [
{ id: 1, name: 'Peter' },
{ id: 2, name: 'John' },
{ id: 3, name: 'Andrew' },
{ id: 4, name: 'Patrick' },
{ id: 5, name: 'Brian' }
];
let array_2 = [
{ id: 1, name: 'not Peter' },
{ id: 80, name: 'not John' },
{ id: 3, name: 'not Andrew' },
{ id: 40, name: 'not Patrick' },
{ id: 5, name: 'not Brian' }
];
array_1.forEach(item_1 => {
for (let i = 0; i < array_2.length; i++) {
item_1.matches = array_2[i].id === item_1.id
}
});
console.log('matched_array', array_1);
The goal here is to add the matches property to each object in array_1 and set it to true/false, based on whether the id matches with any other id from array_2.
In this current example, the result of the matches properties should go like this: true - false - true - false - true. But my current code only sets this property correctly in the last element of the array (array_1).
Obviously it's because my code is not entirely correct, and that's where I'm stuck.

You could first create one object with reduce method that you can then use as a hash table to check if the element with the same id exists in the array 2.
let array_1=[{"id":1,"name":"Peter"},{"id":2,"name":"John"},{"id":3,"name":"Andrew"},{"id":4,"name":"Patrick"},{"id":5,"name":"Brian"}, {"id":6,"name":"Joe"}]
let array_2=[{"id":1,"name":"not Peter"},{"id":80,"name":"not John"},{"id":3,"name":"not Andrew"},{"id":40,"name":"not Patrick"},{"id":5,"name":"not Brian"}]
const o = array_2.reduce((r, e) => (r[e.id] = true, r), {})
const result = array_1.map(e => ({ ...e, matches: o[e.id] || false}))
console.log(result)

I would first collect the ids of array_2 in a Set, sets have a O(1) lookup time so checking if an id is in this set is fast. Then iterate over array_1 and check if the id is present in the created set using has().
let array_1 = [
{ id: 1, name: 'Peter' },
{ id: 2, name: 'John' },
{ id: 3, name: 'Andrew' },
{ id: 4, name: 'Patrick' },
{ id: 5, name: 'Brian' }
];
let array_2 = [
{ id: 1, name: 'not Peter' },
{ id: 80, name: 'not John' },
{ id: 3, name: 'not Andrew' },
{ id: 40, name: 'not Patrick' },
{ id: 5, name: 'not Brian' }
];
const array_2_ids = new Set(array_2.map(item_2 => item_2.id));
array_1.forEach(item_1 => item_1.matches = array_2_ids.has(item_1.id));
console.log('matched_array', array_1);
Your current code doesn't work because the for-loop will update the item_1.matches property for each element in array_2. This means you are overwriting the property each time. This in turn will effectivly result in item_1 only being checked against the last item in array_2.
To make your code work this:
array_1.forEach(item_1 => {
for (let i = 0; i < array_2.length; i++) {
item_1.matches = array_2[i].id === item_1.id
}
});
Should be changed into this:
array_1.forEach(item_1 => {
for (let i = 0; i < array_2.length; i++) {
if (array_2[i].id === item_1.id) {
item_1.matches = true;
return;
}
}
item_1.matches = false;
});

What is an alternative way to update an array of objects?

I have a array of objects. I want to update an object using id.
I am able to do using the map function. Is there an alternative way or more efficient way to update the array?
Here is my code:
https://stackblitz.com/edit/js-xgfwdw?file=index.js
var id = 3
var obj = {
name: "test"
}
let arr = [{
name: "dd",
id: 1
}, {
name: "dzxcd",
id: 3
}, {
name: "nav",
id: 5
}, {
name: "hhh",
id: 4
}]
function getUpdated(obj, id) {
var item = [...arr];
const t = item.map((i) => {
if(i.id==id){
return {
...obj,
id
}
}else {
return i;
}
})
return t
}
console.log(getUpdated(obj,id))
The expected output is correct but I want to achieve the same functionality using an alternative way.
[{
name: "dd",
id: 1
}, {
name: "test",
id: 3
}, {
name: "nav",
id: 5
}, {
name: "hhh",
id: 4
}]

you are in the correct way, basically the bad thing that you are doing is creating new arrays [...arr], when map already gives you a new array.
other things to use, may be the ternary operator and return directly the result of the map function
check here the improvedGetUpdate:
var id = 3;
var obj = {
name: "test"
};
let arr = [{
name: "dd",
id: 1
}, {
name: "dzxcd",
id: 3
}, {
name: "nav",
id: 5
}, {
name: "hhh",
id: 4
}]
function getUpdated(obj, id) {
var item = [...arr];
const t = item.map((i) => {
if (i.id == id) {
return {
...obj,
id
}
} else {
return i;
}
})
return t
}
improvedGetUpdate = (obj, id) => arr.map(i => {
return i.id !== id ? i : {
...obj,
id
}
})
console.log(getUpdated(obj, id))
console.log(improvedGetUpdate(obj, id))

var id = 3
var obj = {
name: "test"
}
let arr = [{
name: "dd",
id: 1
}, {
name: "dzxcd",
id: 3
}, {
name: "nav",
id: 5
}, {
name: "hhh",
id: 4
}]
const result = arr.map((el) => el.id === id ? {...obj, id} : el)
console.log(result);

Use splice method which can be used to update the array too:
var obj = {
id: 3,
name: "test"
}
let arr = [{
name: "dd",
id: 1
}, {
name: "dzxcd",
id: 3
}, {
name: "nav",
id: 5
}, {
name: "hhh",
id: 4
}]
arr.splice(arr.findIndex(({id}) => id === obj.id), 0, obj);
console.log(arr);

#quirimmo suggested short code.
I suggest fast code.
var id = 3;
var obj = {
id: 3,
name: "test"
}
let arr = [{
name: "dd",
id: 1
}, {
name: "dzxcd",
id: 3
}, {
name: "nav",
id: 5
}, {
name: "hhh",
id: 4
}]
var arr2 = [...arr];
console.time('⏱');
arr.splice(arr.findIndex(({id}) => id === obj.id), 0, obj);
console.timeEnd('⏱');
console.time('⏱');
for (let item of arr2) {
if (item.id === id) {
item.name = obj.name;
break;
}
}
console.timeEnd('⏱');
console.log(arr2);

check the difference between two arrays of objects in javascript [duplicate]

This question already has answers here:
How to get the difference between two arrays of objects in JavaScript
(22 answers)
Closed 1 year ago.
I need some help. How can I get the array of the difference on this scenario:
var b1 = [
{ id: 0, name: 'john' },
{ id: 1, name: 'mary' },
{ id: 2, name: 'pablo' },
{ id: 3, name: 'escobar' }
];
var b2 = [
{ id: 0, name: 'john' },
{ id: 1, name: 'mary' }
];
I want the array of difference:
// [{ id: 2, name: 'pablo' }, { id: 3, name: 'escobar' }]
How is the most optimized approach?
I´m trying to filter a reduced array.. something on this line:
var Bfiltered = b1.filter(function (x) {
return x.name !== b2.reduce(function (acc, document, index) {
return (document.name === x.name) ? document.name : false
},0)
});
console.log("Bfiltered", Bfiltered);
// returns { id: 0, name: 'john' }, { id: 2, name: 'pablo' }, { id: 3, name: 'escobar' } ]
Thanks,
Robot

.Filter() and .some() functions will do the trick
var b1 = [
{ id: 0, name: 'john' },
{ id: 1, name: 'mary' },
{ id: 2, name: 'pablo' },
{ id: 3, name: 'escobar' }
];
var b2 = [
{ id: 0, name: 'john' },
{ id: 1, name: 'mary' }
];
var res = b1.filter(item1 =>
!b2.some(item2 => (item2.id === item1.id && item2.name === item1.name)))
console.log(res);

You can use filter to filter/loop thru the array and some to check if id exist on array 2
var b1 = [{ id: 0, name: 'john' }, { id: 1, name: 'mary' }, { id: 2, name: 'pablo' }, { id: 3, name: 'escobar' } ];
var b2 = [{ id: 0, name: 'john' }, { id: 1, name: 'mary' }];
var result = b1.filter(o => !b2.some(v => v.id === o.id));
console.log(result);
Above example will work if array 1 is longer. If you dont know which one is longer you can use sort to arrange the array and use reduce and filter.
var b1 = [{ id: 0, name: 'john' }, { id: 1, name: 'mary' }, { id: 2, name: 'pablo' }, { id: 3, name: 'escobar' } ];
var b2 = [{ id: 0, name: 'john' }, { id: 1, name: 'mary' }];
var result = [b1, b2].sort((a,b)=> b.length - a.length)
.reduce((a,b)=>a.filter(o => !b.some(v => v.id === o.id)));
console.log(result);

Another possibility is to use a Map, allowing you to bring down the time complexity to O(max(n,m)) if dealing with a Map-result is fine for you:
function findArrayDifferences(arr1, arr2) {
const map = new Map();
const maxLength = Math.max(arr1.length, arr2.length);
for (let i = 0; i < maxLength; i++) {
if (i < arr1.length) {
const entry = arr1[i];
if (map.has(entry.id)) {
map.delete(entry.id);
} else {
map.set(entry.id, entry);
}
}
if (i < arr2.length) {
const entry = arr2[i];
if (map.has(entry.id)) {
map.delete(entry.id);
} else {
map.set(entry.id, entry);
}
}
}
return map;
}
const arr1 = [{id:0,name:'john'},{id:1,name:'mary'},{id:2,name:'pablo'},{id:3,name:'escobar'}];
const arr2 = [{id:0,name:'john'},{id:1,name:'mary'},{id:99,name:'someone else'}];
const resultAsArray = [...findArrayDifferences(arr1,arr2).values()];
console.log(resultAsArray);

combine array of objects by key

I am trying to combine/merge 2 array of objects by key in my case id.
Objective:
I am expecting a results where I would have array containing all objects with ids 1,2,3,4 as per example
Order of merging should not affect number of objects in result for example combine(arr1,arr2) or combine(arr2,arr1) should have array with same number of objects
Order of merging can only affect resulting object for example in case of combine(arr1,arr2) arr2 key,values pair can override arr1 key,values just like deep jquery extend $.extend( true, arr1ObJ,arr2ObJ );
JSFIDDLE: https://jsfiddle.net/bababalcksheep/u2c05nyj/
Sample Data:
var arr1 = [{
id: 1,
name: "fred",
title: "boss"
}, {
id: 2,
name: "jim",
title: "nobody"
}, {
id: 3,
name: "bob",
title: "dancer"
}];
var arr2 = [{
id: 1,
wage: "300",
rate: "day"
}, {
id: 2,
wage: "10",
rate: "hour"
}, {
id: 4,
wage: "500",
rate: "week"
}];
var Result = [{
"id": 1,
"name": "fred",
"title": "boss",
"wage": "300",
"rate": "day"
}, {
"id": 2,
"name": "jim",
"title": "nobody",
"wage": "10",
"rate": "hour"
}, {
id: 3,
name: "bob",
title: "dancer"
}, {
id: 4,
wage: "500",
rate: "week"
}];

Here's a solution. It basically goes through each element of arr2 and checks to see if there's an element with a matching ID arr1. If so, it updates the matching element in arr1 with arr2's values. If there is no match, it simply pushes the element in arr2 onto arr1.
var arr1 = [{id: 1,name: 'fred',title: 'boss'},
{id: 2,name: 'jim',title: 'nobody'},
{id: 3,name: 'bob',title: 'dancer'}];
var arr2 = [{id: 1,wage: '300',rate: 'day'},
{id: 2,wage: '10',rate:'hour'},
{id: 4,wage: '500',rate: 'week'}];
function combineArrays(arr1, arr2) {
for(var i = 0; i < arr2.length; i++) {
// check if current object exists in arr1
var idIndex = hasID(arr2[i]['id'], arr1);
if(idIndex >= 0){
//update
for(var key in arr2[i]){
arr1[idIndex][key] = arr2[i][key];
}
} else {
//insert
arr1.push(arr2[i]);
}
}
return arr1;
}
//Returns position in array that ID exists
function hasID(id, arr) {
for(var i = 0; i < arr.length; i ++) {
if(arr[i]['id'] === id)
{
return i;
}
}
return -1;
}
var combine = combineArrays(arr1, arr2);
output(combine);
/* pretty Print */
function output(inp) {
var str = JSON.stringify(inp, undefined, 4);
$('body').append($('<pre/>').html(str));
}
var arr1 = [{
id: 1,
name: 'fred',
title: 'boss'
}, {
id: 2,
name: 'jim',
title: 'nobody'
}, {
id: 3,
name: 'bob',
title: 'dancer'
}];
var arr2 = [{
id: 1,
wage: '300',
rate: 'day'
}, {
id: 2,
wage: '10',
rate: 'hour'
}, {
id: 4,
wage: '500',
rate: 'week'
}];
function combineArrays(arr1, arr2) {
for (var i = 0; i < arr2.length; i++) {
var idIndex = hasID(arr2[i]['id'], arr1);
if (idIndex >= 0) {
for (var key in arr2[i]) {
arr1[idIndex][key] = arr2[i][key];
}
} else {
arr1.push(arr2[i]);
}
}
return arr1;
}
function hasID(id, arr) {
for (var i = 0; i < arr.length; i++) {
if (arr[i]['id'] === id) {
return i;
}
}
return -1;
}
var combine = combineArrays(arr1, arr2);
output(combine);
/* pretty Print */
function output(inp) {
var str = JSON.stringify(inp, undefined, 4);
$('body').append($('<pre/>').html(str));
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

How about something along the lines of this:
function combineArrays(arr1, arr2, keyFunc) {
var combined = [],
keys1 = arr1.map(keyFunc),
keys2 = arr2.map(keyFunc),
pos1 = keys1.map(function (id) {
return keys2.indexOf(id);
}),
pos2 = keys2.map(function (id) {
return keys1.indexOf(id);
});
arr1.forEach(function (item, i) {
combined.push( $.extend(item, arr2[pos1[i]]) );
});
arr2.forEach(function (item, i) {
if (pos2[i] === -1) combined.push( item );
});
return combined;
}
used as
var combine = combineArrays(arr1, arr2, function (item) {
return item.id;
});
var arr1 = [
{ id: 1, name: 'fred', title: 'boss' },
{ id: 2, name: 'jim', title: 'nobody' },
{ id: 3, name: 'bob', title: 'dancer' }
];
var arr2 = [
{ id: 1, wage: '300', rate: 'day' },
{ id: 2, wage: '10', rate: 'hour' },
{ id: 4, wage: '500', rate: 'week' }
];
function combineArrays(arr1, arr2, keyFunc) {
var combined = [],
keys1 = arr1.map(keyFunc),
keys2 = arr2.map(keyFunc),
pos1 = keys1.map(function (id) {
return keys2.indexOf(id);
}),
pos2 = keys2.map(function (id) {
return keys1.indexOf(id);
});
arr1.forEach(function (item, i) {
combined.push( $.extend(item, arr2[pos1[i]]) );
});
arr2.forEach(function (item, i) {
if (pos2[i] === -1) combined.push( item );
});
return combined;
}
var combine = combineArrays(arr1, arr2, function (item) {
return item.id;
});
output(combine);
//
//
//
/* pretty Print */
function output(inp) {
var str = JSON.stringify(inp, undefined, 4);
$('body').append($('<pre/>').html(str));
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>

How do I remove duplicate objects in an array by field in Javascript?

I have an array of objects:
[{
id: 1,
name: 'kitten'
}, {
id: 2,
name: 'kitten'
},{
id: 3,
name: 'cat
}]
How do I remove the second kitten? Sorting into an array of names doesn't work, because I can't know if I am deleting id 1 or or id 2. So, I'm not quite sure how to do this.

You can use an additional hash-map to store names found so far. When you process a next object if it's name is already in the hash-map it is a duplicate and you can remove it.
var duplicates = {};
for (var i = 0; i < array.length) {
var obj = array[i];
if (! duplicates[obj.name]) {
duplicates[obj.name] = 1;
i++;
} else {
array.splice(i, 1);
}
}

there is the lodash library.
You could use the uniq
var array = [{
id: 1,
name: 'kitten'
}, {
id: 2,
name: 'kitten'
},{
id: 3,
name: 'cat'
}];
var asd = _.uniq(array,'name');
console.log(asd);
Gives an output:
[ { id: 1, name: 'kitten' }, { id: 3, name: 'cat' } ]
as it written in the documentation "only the first occurence of each element is kept".

var arr =[{
id: 1,
name: 'kitten'
}, {
id: 2,
name: 'kitten'
},{
id: 3,
name: 'cat'
}];
var results = [];
var idsSeen = {}, idSeenValue = {};
for (var i = 0, len = arr.length, name; i < len; ++i) {
name = arr[i].name;
if (idsSeen[name] !== idSeenValue) {
results.push(arr[i]);
idsSeen[name] = idSeenValue;
}
}
console.log(results);

Develop Reference

JavaScript is the programming language of the Web.

using javascript filter() with a flag - javascript

Related

Set object property in an array true/false, whether the id matches with any id from another array of objects

What is an alternative way to update an array of objects?

check the difference between two arrays of objects in javascript [duplicate]

combine array of objects by key

How do I remove duplicate objects in an array by field in Javascript?

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