Related
Task
A list
Objects, as generic blobs of values, can be used to build all sorts of data structures. A common data structure is the list (not to be confused with the array). A list is a nested set of objects, with the first object holding a reference to the second, the second to the third, and so on.
var list = {
value: 1,
rest: {
value: 2,
rest: {
value: 3,
rest: null
}
}
};
The resulting objects form a chain, like this:
A linked list
A nice thing about lists is that they can share parts of their structure. For example, if I create two new values {value: 0, rest: list} and {value: -1, rest: list} (with list referring to the variable defined earlier), they are both independent lists, but they share the structure that makes up their last three elements. In addition, the original list is also still a valid three-element list.
Write a function arrayToList that builds up a data structure like the previous one when given [1, 2, 3]
The over all goal is to create a function that creates a list structure as mentioned in the Exercise "A list" in the Data Structures Chapter.
function arrayToList(array){
var list = {};
var i = 0;
var rest = ((i < array.length) ? (i++,{value: array[i],rest: rest}): null) ;
list = {
value: array[0],
rest: rest
}
return list;
}
What I was hoping to accomplish was use the rest variable to call itself until the var i was greater than the array length, but when I run the code the rest property return undefined... my question is why does it not behave as recursive call to the same ternary var rest. I am fairly new to javascript so any advise or articles that would help me understand why this happens would be great.
You can use Array.prototype.reduce()
var list = {};
var arr = [1,2,3];
arr.reduce((o, prop, index, array) => {
o["value"] = prop;
o["rest"] = index < array.length -1 ? {} : null;
return o["rest"]
}, list);
console.log(list);
As commenters have said, you aren't actually making this function recursive - it never calls itself.
To achieve what you want you'd have to do this:
function arrayToList(array){
var list = {};
var rest = ((array.length) ? (arrayToList(array.slice(1))) : null) ;
list = {
value: array[0],
rest: rest
}
return list;
}
In modern javascript, you can simply do this:
var arrayToList = array => array.slice().reverse().reduce((rest, value) => ({ value, rest }), { rest:null });
which, after running it through a transpiler, becomes
var arrayToList = function arrayToList(array) {
return array.slice().reverse().reduce(function (rest, value) {
return { value: value, rest: rest };
}, { rest:null });
};
var array = [1,2,3,4,5];
var arrayToList = function(array) {
var list = {};
var array = array.reverse();
var arrLength = array.length;
for (var i = 0; i < arrLength; i++) {
var newList = function() {
if (i) {
return list;
} else {
return null
}
}
list = {
value: array[i],
list: newList()
}
}
return list;
}
console.log(arrayToList(array));
I also learn javascript from that book and i struggled with this one.
I think this is more close to what we have learned in the book so far.
Using reduce function is also a great way to resolve this , but it is not yet presented in the book and we presume we have no idea how to use it.
I have an array like
vendors = [{
Name: 'Magenic',
ID: 'ABC'
},
{
Name: 'Microsoft',
ID: 'DEF'
} // and so on...
];
How do I check this array to see if "Magenic" exists? I don't want to loop, unless I have to. I'm working with potentially a couple thousand records.
No need to reinvent the wheel loop, at least not explicitly (using arrow functions, modern browsers only):
if (vendors.filter(e => e.Name === 'Magenic').length > 0) {
/* vendors contains the element we're looking for */
}
or, better yet, use some as it allows the browser to stop as soon as one element is found that matches, so it's going to be faster:
if (vendors.some(e => e.Name === 'Magenic')) {
/* vendors contains the element we're looking for */
}
or the equivalent (in this case) find:
if (vendors.find(e => e.Name === 'Magenic')) {
/* same result as above, but a different function return type */
}
And you can even get the position of that element by using findIndex:
const i = vendors.findIndex(e => e.Name === 'Magenic');
if (i > -1) {
/* vendors contains the element we're looking for, at index "i" */
}
And if you need compatibility with lousy browsers then your best bet is:
if (vendors.filter(function(e) { return e.Name === 'Magenic'; }).length > 0) {
/* vendors contains the element we're looking for */
}
2018 edit: This answer is from 2011, before browsers had widely supported array filtering methods and arrow functions. Have a look at CAFxX's answer.
There is no "magic" way to check for something in an array without a loop. Even if you use some function, the function itself will use a loop. What you can do is break out of the loop as soon as you find what you're looking for to minimize computational time.
var found = false;
for(var i = 0; i < vendors.length; i++) {
if (vendors[i].Name == 'Magenic') {
found = true;
break;
}
}
No loop necessary. Three methods that come to mind:
Array.prototype.some()
This is the most exact answer for your question, i.e. "check if something exists", implying a bool result. This will be true if there are any 'Magenic' objects, false otherwise:
let hasMagenicVendor = vendors.some( vendor => vendor['Name'] === 'Magenic' )
Array.prototype.filter()
This will return an array of all 'Magenic' objects, even if there is only one (will return a one-element array):
let magenicVendors = vendors.filter( vendor => vendor['Name'] === 'Magenic' )
If you try to coerce this to a boolean, it will not work, as an empty array (no 'Magenic' objects) is still truthy. So just use magenicVendors.length in your conditional.
Array.prototype.find()
This will return the first 'Magenic' object (or undefined if there aren't any):
let magenicVendor = vendors.find( vendor => vendor['Name'] === 'Magenic' );
This coerces to a boolean okay (any object is truthy, undefined is falsy).
Note: I'm using vendor["Name"] instead of vendor.Name because of the weird casing of the property names.
Note 2: No reason to use loose equality (==) instead of strict equality (===) when checking the name.
The accepted answer still works but now we have an ECMAScript 6 native methods [Array.find][1] and [Array.some][2] to achieve the same effect.
Array.some
Use some If you only want to determine if an element exists i.e. you need a true/false determination.
Quoting MDN:
The some() method tests whether at least one element in the array passes the test implemented by the provided function. It returns true if, in the array, it finds an element for which the provided function returns true; otherwise it returns false. It doesn't modify the array.
Array.find
Use find if you want to get the matched object from array else returns undefined.
Quoting MDN:
The find() method returns the value of the first element in the provided array that satisfies the provided testing function. If no values satisfy the testing function, undefined is returned.
var arr = [
{
id: 21,
label: 'Banana',
},
{
id: 22,
label: 'Apple',
}
]
/* note : data is the actual object that matched search criteria
or undefined if nothing matched */
var data = arr.find(function(ele) {
return ele.id === 21;
});
if (data) {
console.log('found');
console.log(data); // This is entire object i.e. `item` not boolean
}
/* note : doesExist is a boolean thats true or false depending on of whether the data was found or not */
var doesExist = arr.some(function(ele) {
return ele.id === 21;
});
See my jsfiddle link There is a polyfill for IE provided by mozilla
Here's the way I'd do it
const found = vendors.some(item => item.Name === 'Magenic');
array.some() method checks if there is at least one value in an array that matches criteria and returns a boolean.
From here on you can go with:
if (found) {
// do something
} else {
// do something else
}
Unless you want to restructure it like this:
vendors = {
Magenic: {
Name: 'Magenic',
ID: 'ABC'
},
Microsoft: {
Name: 'Microsoft',
ID: 'DEF'
} and so on...
};
to which you can do if(vendors.Magnetic)
You will have to loop
May be too late, but javascript array has two methods some and every method that returns a boolean and can help you achieve this.
I think some would be most appropriate for what you intend to achieve.
vendors.some( vendor => vendor['Name'] !== 'Magenic' )
Some validates that any of the objects in the array satisfies the given condition.
vendors.every( vendor => vendor['Name'] !== 'Magenic' )
Every validates that all the objects in the array satisfies the given condition.
As per ECMAScript 6 specification, you can use findIndex.
const magenicIndex = vendors.findIndex(vendor => vendor.Name === 'Magenic');
magenicIndex will hold either 0 (which is the index in the array) or -1 if it wasn't found.
As the OP has asked the question if the key exists or not.
A more elegant solution that will return boolean using ES6 reduce function can be
const magenicVendorExists = vendors.reduce((accumulator, vendor) => (accumulator||vendor.Name === "Magenic"), false);
Note: The initial parameter of reduce is a false and if the array has the key it will return true.
Hope it helps for better and cleaner code implementation
You cannot without looking into the object really.
You probably should change your structure a little, like
vendors = {
Magenic: 'ABC',
Microsoft: 'DEF'
};
Then you can just use it like a lookup-hash.
vendors['Microsoft']; // 'DEF'
vendors['Apple']; // undefined
const check = vendors.find((item)=>item.Name==='Magenic')
console.log(check)
Try this code.
If the item or element is present then the output will show you that element. If it is not present then the output will be 'undefined'.
Testing for array elements:
JS Offers array functions which allow you to achieve this relatively easily. They are the following:
Array.prototype.filter: Takes a callback function which is a test, the array is then iterated over with is callback and filtered according to this callback. A new filtered array is returned.
Array.prototype.some: Takes a callback function which is a test, the array is then iterated over with is callback and if any element passes the test, the boolean true is returned. Otherwise false is returned
The specifics are best explained via an example:
Example:
vendors = [
{
Name: 'Magenic',
ID: 'ABC'
},
{
Name: 'Microsoft',
ID: 'DEF'
} //and so on goes array...
];
// filter returns a new array, we instantly check if the length
// is longer than zero of this newly created array
if (vendors.filter(company => company.Name === 'Magenic').length ) {
console.log('I contain Magenic');
}
// some would be a better option then filter since it directly returns a boolean
if (vendors.some(company => company.Name === 'Magenic')) {
console.log('I also contain Magenic');
}
Browser support:
These 2 function are ES6 function, not all browsers might support them. To overcome this you can use a polyfill. Here is the polyfill for Array.prototype.some (from MDN):
if (!Array.prototype.some) {
Array.prototype.some = function(fun, thisArg) {
'use strict';
if (this == null) {
throw new TypeError('Array.prototype.some called on null or undefined');
}
if (typeof fun !== 'function') {
throw new TypeError();
}
var t = Object(this);
var len = t.length >>> 0;
for (var i = 0; i < len; i++) {
if (i in t && fun.call(thisArg, t[i], i, t)) {
return true;
}
}
return false;
};
}
Simplest method so far:
if (vendors.findIndex(item => item.Name == "Magenic") == -1) {
//not found item
} else {
//found item
}
My approach to solving this problem is to use ES6 and creating a function that does the check for us. The benefit of this function is that it can be reusable through out your project to check any array of objects given the key and the value to check.
ENOUGH TALK, LET'S SEE THE CODE
Array
const ceos = [
{
name: "Jeff Bezos",
company: "Amazon"
},
{
name: "Mark Zuckerberg",
company: "Facebook"
},
{
name: "Tim Cook",
company: "Apple"
}
];
Function
const arrayIncludesInObj = (arr, key, valueToCheck) => {
return arr.some(value => value[key] === valueToCheck);
}
Call/Usage
const found = arrayIncludesInObj(ceos, "name", "Tim Cook"); // true
const found = arrayIncludesInObj(ceos, "name", "Tim Bezos"); // false
2021 Solution*
Lodash .some (docs) is a clean solution, if you use the _matchesProperty (docs) shorthand:
_.some(VENDORS, ['Name', 'Magenic'])
Explanation
This will iterate through the VENDORS Array looking for an element Object with the Name key having a value of the String 'Magenic'. Once it finds this element, it returns true and stops iterating. If it doesn't find the element after looking through the entire Array, it returns false.
Code snippet
const VENDORS = [{ Name: 'Magenic', ID: 'ABC' }, { Name: 'Microsoft', ID: 'DEF' }];
console.log(_.some(VENDORS, ['Name', 'Magenic'])); // true
<script src="https://cdn.jsdelivr.net/npm/lodash#4.17.20/lodash.min.js"></script>
* Note that this uses the popular lodash library to achieve the simplest/shortest possible solution. I'm offering this as an alternative to the existing vanilla JS solutions, for those who are interested.
You have to loop, there is no way around it.
function seekVendor(vendors, name) {
for (var i=0, l=vendors.length; i<l; i++) {
if (typeof vendors[i] == "object" && vendors[i].Name === name) {
return vendors[i];
}
}
}
Of course you could use a library like linq.js to make this more pleasing:
Enumerable.From(vendors).Where("$.Name == 'Magenic'").First();
(see jsFiddle for a demo)
I doubt that linq.js will be faster than a straight-forward loop, but it certainly is more flexible when things get a little more complicated.
Correct me if i'm wrong..
i could have used forEach method like this,
var found=false;
vendors.forEach(function(item){
if(item.name === "name"){
found=true;
}
});
Nowadays i'm used to it ,because of it simplicity and self explanatory word.
Thank you.
Functions map, filter, find, and similar are slower than the simple loop.
For me they also less readable than the simple loop and harder to debug. Using them looks like a kind of irrational ritual.
Better have something like this:
arrayHelper = {
arrayContainsObject: function (array, object, key){
for (let i = 0; i < array.length; i++){
if (object[key] === array[i][key]){
return true;
}
}
return false;
}
};
And use it like this with given OP example:
vendors = [{
Name: 'Magenic',
ID: 'ABC'
},
{
Name: 'Microsoft',
ID: 'DEF'
}
];
let abcObject = {ID: 'ABC', Name: 'Magenic'};
let isContainObject = arrayHelper.arrayContainsObject(vendors, abcObject, 'ID');
if you're using jquery you can take advantage of grep to create array with all matching objects:
var results = $.grep(vendors, function (e) {
return e.Name == "Magenic";
});
and then use the results array:
for (var i=0, l=results.length; i<l; i++) {
console.log(results[i].ID);
}
You can use lodash. If lodash library is too heavy for your application consider chunking out unnecessary function not used.
let newArray = filter(_this.props.ArrayOne, function(item) {
return find(_this.props.ArrayTwo, {"speciesId": item.speciesId});
});
This is just one way to do this. Another one can be:
var newArray= [];
_.filter(ArrayOne, function(item) {
return AllSpecies.forEach(function(cItem){
if (cItem.speciesId == item.speciesId){
newArray.push(item);
}
})
});
console.log(arr);
The above example can also be rewritten without using any libraries like:
var newArray= [];
ArrayOne.filter(function(item) {
return ArrayTwo.forEach(function(cItem){
if (cItem.speciesId == item.speciesId){
newArray.push(item);
}
})
});
console.log(arr);
Hope my answer helps.
Many answers here are good and pretty easy. But if your array of object is having a fixed set of value then you can use below trick:
Map all the name in a object.
vendors = [
{
Name: 'Magenic',
ID: 'ABC'
},
{
Name: 'Microsoft',
ID: 'DEF'
}
];
var dirtyObj = {}
for(var count=0;count<vendors.length;count++){
dirtyObj[vendors[count].Name] = true //or assign which gives you true.
}
Now this dirtyObj you can use again and again without any loop.
if(dirtyObj[vendor.Name]){
console.log("Hey! I am available.");
}
To compare one object to another, I combine a for in loop (used to loop through objects) and some().
You do not have to worry about an array going out of bounds etc, so that saves some code. Documentation on .some can be found here
var productList = [{id: 'text3'}, {id: 'text2'}, {id: 'text4', product: 'Shampoo'}]; // Example of selected products
var theDatabaseList = [{id: 'text1'}, {id: 'text2'},{id: 'text3'},{id:'text4', product: 'shampoo'}];
var objectsFound = [];
for(let objectNumber in productList){
var currentId = productList[objectNumber].id;
if (theDatabaseList.some(obj => obj.id === currentId)) {
// Do what you need to do with the matching value here
objectsFound.push(currentId);
}
}
console.log(objectsFound);
An alternative way I compare one object to another is to use a nested for loop with Object.keys().length to get the amount of objects in the array. Code below:
var productList = [{id: 'text3'}, {id: 'text2'}, {id: 'text4', product: 'Shampoo'}]; // Example of selected products
var theDatabaseList = [{id: 'text1'}, {id: 'text2'},{id: 'text3'},{id:'text4', product: 'shampoo'}];
var objectsFound = [];
for(var i = 0; i < Object.keys(productList).length; i++){
for(var j = 0; j < Object.keys(theDatabaseList).length; j++){
if(productList[i].id === theDatabaseList[j].id){
objectsFound.push(productList[i].id);
}
}
}
console.log(objectsFound);
To answer your exact question, if are just searching for a value in an object, you can use a single for in loop.
var vendors = [
{
Name: 'Magenic',
ID: 'ABC'
},
{
Name: 'Microsoft',
ID: 'DEF'
}
];
for(var ojectNumbers in vendors){
if(vendors[ojectNumbers].Name === 'Magenic'){
console.log('object contains Magenic');
}
}
Alternatively you can do:
const find = (key, needle) => return !!~vendors.findIndex(v => (v[key] === needle));
var without2 = (arr, args) => arr.filter(v => v.id !== args.id);
Example:
without2([{id:1},{id:1},{id:2}],{id:2})
Result:
without2([{id:1},{id:1},{id:2}],{id:2})
You can try this its work for me.
const _ = require('lodash');
var arr = [
{
name: 'Jack',
id: 1
},
{
name: 'Gabriel',
id: 2
},
{
name: 'John',
id: 3
}
]
function findValue(arr,value) {
return _.filter(arr, function (object) {
return object['name'].toLowerCase().indexOf(value.toLowerCase()) >= 0;
});
}
console.log(findValue(arr,'jack'))
//[ { name: 'Jack', id: 1 } ]
const a = [{one:2},{two:2},{two:4}]
const b = a.filter(val => "two" in val).length;
if (b) {
...
}
I would rather go with regex.
If your code is as follows,
vendors = [
{
Name: 'Magenic',
ID: 'ABC'
},
{
Name: 'Microsoft',
ID: 'DEF'
}
];
I would recommend
/"Name":"Magenic"/.test(JSON.stringify(vendors))
I have the following array:
var tst =
[
{"topicId":1,"subTopicId":1,"topicName":"a","subTopicName":"w"},
{"topicId":1,"subTopicId":2,"topicName":"b","subTopicName":"x"},
{"topicId":1,"subTopicId":3,"topicName":"c","subTopicName":"y"},
{"topicId":2,"subTopicId":4,"topicName":"c","subTopicName":"z"}
]
Is there an easy way that I can map that to this kind of array where topicId > id and topicName > name:
var t =
[
{"id":1,"name":"a"},
{"id":2,"name":"c"}
]
I am using a modern browser and I also have _lodash if that helps. Note that there will be about 100 rows in the tst array so I don't need a very optimized solution. A simple and easy to maintain solution would be more important.
MOST RECENT
_.uniqBy is now preferable
Full working example here
var tst = [
{"topicId":1,"subTopicId":1,"topicName":"a","subTopicName1":"w"},
{"topicId":2,"subTopicId":2,"topicName":"b","subTopicName2":"x"},
{"topicId":3,"subTopicId":3,"topicName":"c","subTopicName3":"y"},
{"topicId":1,"subTopicId":4,"topicName":"c","subTopicName4":"z"}
];
var result = _.map(_.uniqBy(tst, 'topicId'), function (item) {
return {
id: item.topicId,
name: item.topicName
};
});
console.log(result);
LEGACY
http://lodash.com/docs#uniq is a good start
_.uniq([{ 'x': 1 }, { 'x': 2 }, { 'x': 1 }], 'x');
Your code would look like this to get topics unique by id
var t = _.uniq(tst, 'topicId');
EDIT
I made a jsfiddle
http://jsfiddle.net/q5HNw/
UPDATE
Removed unnecessary uniqueness of names
http://jsfiddle.net/q5HNw/1/
I am one of those guys that use native functions :)
var results = tst.reduce(function(res,topic){
var exists = res.some(function(t){ return (t.id === topic.topicId && t.name === topic.topicName);});
if (!exists){
res.push({"id": topic.topicId, "name": topic.topicName});
}
return res; },[]);
Lodash version
I am not an expert using lodash, probably I will try something like this:
var results = _.reduce(tst, function(res, topic){
var exists = _.findIndex(res, function(t){
return (t.id === topic.topicId && t.name === topic.topicName);
});
if (exists === -1){
res.push({"id": topic.topicId, "name": topic.topicName});
}
return res;
},[]);
Using ECMAScript 2015 Array.prototype.find()
The find() method returns the value of the first element in the array that satisfies the provided testing function. Otherwise undefined is returned.
let tst = [
{"topicId":1,"subTopicId":1,"topicName":"a","subTopicName":"w"},
{"topicId":1,"subTopicId":2,"topicName":"b","subTopicName":"x"},
{"topicId":1,"subTopicId":3,"topicName":"c","subTopicName":"y"},
{"topicId":2,"subTopicId":4,"topicName":"c","subTopicName":"z"},
];
let t = [];
tst.forEach(obj => {
// Check if the id already exists in the array 't'
if (!t.find((self) => self.id === obj.topicId)) {
// If not, pushes obj to t
t.push({
id: obj.topicId,
name: obj.topicName
});
}
});
console.log(t);
You can also compare more than one property:
let tst = [
{"topicId":1,"subTopicId":1,"topicName":"a","subTopicName":"w"},
{"topicId":1,"subTopicId":2,"topicName":"b","subTopicName":"x"},
{"topicId":1,"subTopicId":3,"topicName":"c","subTopicName":"y"},
{"topicId":2,"subTopicId":4,"topicName":"c","subTopicName":"z"},
];
let t = [];
tst.forEach(obj => {
// Check if the 'id' and 'subId' already exist in t
if (!t.find((self) => self.id === obj.topicId && self.subId === obj.subTopicId)) {
// If not, pushes obj to t
t.push({
id: obj.topicId,
subId: obj.subTopicId,
name: obj.topicName
});
}
});
console.log(t);
I can imagine this has been asked a few times but I literally cannot find an example of a solution to the specific problem I'm trying to figure out.
So I have an object, like so:
var collection = [{ id: 0 }, { id: 1 }, { id: 2 }];
I then have an array, which is the 'order', like so:
var order = [2, 0, 1];
I want to use the 'order' array to reorder the collection in that specific order. I've been trying quite a few solutions with the .sort function, but I can't find one that fits. Can anyone enlighten me? Probably simple, I'm hoping.
You can use the sort() method to accomplish this using indexOf:
collection.sort(function(a, b){
return order.indexOf(a.id) > order.indexOf(b.id);
});
You can use indexOf function on the order array in the custom sort function, like this:
collection.sort(function(x, y) {
return order.indexOf(x.id) > order.indexOf(y.id);
});
seems to be as easy as that:
var collection = [{ id: 0 }, { id: 1 }, { id: 2 }];
var order = [2, 0, 1];
var sorted = [];
for(var i=0,c=order.length;i<c;i++){
sorted.push(collection[order[i]]);
}
Try that:
var collection = [{ id: 0 }, { id: 1 }, { id: 2 }];
var order = [2, 0, 1];
var sortedCollection = [];
for ( var i = 0; i < order.length; i++ )
sortedCollection.push(collection[order[i]]);
console.log(sortedCollection);
The thing you want to avoid here is scanning through either of these arrays more than you have to.
Here's one solution that avoids this:
/*
* Map the indexes of the objects in collection to their final location
*/
var sortIndex = {};
order.forEach(function(value, index) {
sortIndex[value] = index;
});
/*
* Put the objects in collection into their new, sorted collection
*/
var sortedCollection = [];
collection.forEach(function(value) {
var sortedLocation = sortIndex[value.id];
sortedCollection[sortedLocation] = value;
});
Thus, we have a single scan through each of the arrays, keeping the work down to a minimum.
I've used forEach here as a convenience; you could use a library like Lodash or Underscore, or rewrite this to use explicit iteration over the arrays.
I have an array like
vendors = [{
Name: 'Magenic',
ID: 'ABC'
},
{
Name: 'Microsoft',
ID: 'DEF'
} // and so on...
];
How do I check this array to see if "Magenic" exists? I don't want to loop, unless I have to. I'm working with potentially a couple thousand records.
No need to reinvent the wheel loop, at least not explicitly (using arrow functions, modern browsers only):
if (vendors.filter(e => e.Name === 'Magenic').length > 0) {
/* vendors contains the element we're looking for */
}
or, better yet, use some as it allows the browser to stop as soon as one element is found that matches, so it's going to be faster:
if (vendors.some(e => e.Name === 'Magenic')) {
/* vendors contains the element we're looking for */
}
or the equivalent (in this case) find:
if (vendors.find(e => e.Name === 'Magenic')) {
/* same result as above, but a different function return type */
}
And you can even get the position of that element by using findIndex:
const i = vendors.findIndex(e => e.Name === 'Magenic');
if (i > -1) {
/* vendors contains the element we're looking for, at index "i" */
}
And if you need compatibility with lousy browsers then your best bet is:
if (vendors.filter(function(e) { return e.Name === 'Magenic'; }).length > 0) {
/* vendors contains the element we're looking for */
}
2018 edit: This answer is from 2011, before browsers had widely supported array filtering methods and arrow functions. Have a look at CAFxX's answer.
There is no "magic" way to check for something in an array without a loop. Even if you use some function, the function itself will use a loop. What you can do is break out of the loop as soon as you find what you're looking for to minimize computational time.
var found = false;
for(var i = 0; i < vendors.length; i++) {
if (vendors[i].Name == 'Magenic') {
found = true;
break;
}
}
No loop necessary. Three methods that come to mind:
Array.prototype.some()
This is the most exact answer for your question, i.e. "check if something exists", implying a bool result. This will be true if there are any 'Magenic' objects, false otherwise:
let hasMagenicVendor = vendors.some( vendor => vendor['Name'] === 'Magenic' )
Array.prototype.filter()
This will return an array of all 'Magenic' objects, even if there is only one (will return a one-element array):
let magenicVendors = vendors.filter( vendor => vendor['Name'] === 'Magenic' )
If you try to coerce this to a boolean, it will not work, as an empty array (no 'Magenic' objects) is still truthy. So just use magenicVendors.length in your conditional.
Array.prototype.find()
This will return the first 'Magenic' object (or undefined if there aren't any):
let magenicVendor = vendors.find( vendor => vendor['Name'] === 'Magenic' );
This coerces to a boolean okay (any object is truthy, undefined is falsy).
Note: I'm using vendor["Name"] instead of vendor.Name because of the weird casing of the property names.
Note 2: No reason to use loose equality (==) instead of strict equality (===) when checking the name.
The accepted answer still works but now we have an ECMAScript 6 native methods [Array.find][1] and [Array.some][2] to achieve the same effect.
Array.some
Use some If you only want to determine if an element exists i.e. you need a true/false determination.
Quoting MDN:
The some() method tests whether at least one element in the array passes the test implemented by the provided function. It returns true if, in the array, it finds an element for which the provided function returns true; otherwise it returns false. It doesn't modify the array.
Array.find
Use find if you want to get the matched object from array else returns undefined.
Quoting MDN:
The find() method returns the value of the first element in the provided array that satisfies the provided testing function. If no values satisfy the testing function, undefined is returned.
var arr = [
{
id: 21,
label: 'Banana',
},
{
id: 22,
label: 'Apple',
}
]
/* note : data is the actual object that matched search criteria
or undefined if nothing matched */
var data = arr.find(function(ele) {
return ele.id === 21;
});
if (data) {
console.log('found');
console.log(data); // This is entire object i.e. `item` not boolean
}
/* note : doesExist is a boolean thats true or false depending on of whether the data was found or not */
var doesExist = arr.some(function(ele) {
return ele.id === 21;
});
See my jsfiddle link There is a polyfill for IE provided by mozilla
Here's the way I'd do it
const found = vendors.some(item => item.Name === 'Magenic');
array.some() method checks if there is at least one value in an array that matches criteria and returns a boolean.
From here on you can go with:
if (found) {
// do something
} else {
// do something else
}
Unless you want to restructure it like this:
vendors = {
Magenic: {
Name: 'Magenic',
ID: 'ABC'
},
Microsoft: {
Name: 'Microsoft',
ID: 'DEF'
} and so on...
};
to which you can do if(vendors.Magnetic)
You will have to loop
May be too late, but javascript array has two methods some and every method that returns a boolean and can help you achieve this.
I think some would be most appropriate for what you intend to achieve.
vendors.some( vendor => vendor['Name'] !== 'Magenic' )
Some validates that any of the objects in the array satisfies the given condition.
vendors.every( vendor => vendor['Name'] !== 'Magenic' )
Every validates that all the objects in the array satisfies the given condition.
As per ECMAScript 6 specification, you can use findIndex.
const magenicIndex = vendors.findIndex(vendor => vendor.Name === 'Magenic');
magenicIndex will hold either 0 (which is the index in the array) or -1 if it wasn't found.
As the OP has asked the question if the key exists or not.
A more elegant solution that will return boolean using ES6 reduce function can be
const magenicVendorExists = vendors.reduce((accumulator, vendor) => (accumulator||vendor.Name === "Magenic"), false);
Note: The initial parameter of reduce is a false and if the array has the key it will return true.
Hope it helps for better and cleaner code implementation
You cannot without looking into the object really.
You probably should change your structure a little, like
vendors = {
Magenic: 'ABC',
Microsoft: 'DEF'
};
Then you can just use it like a lookup-hash.
vendors['Microsoft']; // 'DEF'
vendors['Apple']; // undefined
const check = vendors.find((item)=>item.Name==='Magenic')
console.log(check)
Try this code.
If the item or element is present then the output will show you that element. If it is not present then the output will be 'undefined'.
Testing for array elements:
JS Offers array functions which allow you to achieve this relatively easily. They are the following:
Array.prototype.filter: Takes a callback function which is a test, the array is then iterated over with is callback and filtered according to this callback. A new filtered array is returned.
Array.prototype.some: Takes a callback function which is a test, the array is then iterated over with is callback and if any element passes the test, the boolean true is returned. Otherwise false is returned
The specifics are best explained via an example:
Example:
vendors = [
{
Name: 'Magenic',
ID: 'ABC'
},
{
Name: 'Microsoft',
ID: 'DEF'
} //and so on goes array...
];
// filter returns a new array, we instantly check if the length
// is longer than zero of this newly created array
if (vendors.filter(company => company.Name === 'Magenic').length ) {
console.log('I contain Magenic');
}
// some would be a better option then filter since it directly returns a boolean
if (vendors.some(company => company.Name === 'Magenic')) {
console.log('I also contain Magenic');
}
Browser support:
These 2 function are ES6 function, not all browsers might support them. To overcome this you can use a polyfill. Here is the polyfill for Array.prototype.some (from MDN):
if (!Array.prototype.some) {
Array.prototype.some = function(fun, thisArg) {
'use strict';
if (this == null) {
throw new TypeError('Array.prototype.some called on null or undefined');
}
if (typeof fun !== 'function') {
throw new TypeError();
}
var t = Object(this);
var len = t.length >>> 0;
for (var i = 0; i < len; i++) {
if (i in t && fun.call(thisArg, t[i], i, t)) {
return true;
}
}
return false;
};
}
Simplest method so far:
if (vendors.findIndex(item => item.Name == "Magenic") == -1) {
//not found item
} else {
//found item
}
My approach to solving this problem is to use ES6 and creating a function that does the check for us. The benefit of this function is that it can be reusable through out your project to check any array of objects given the key and the value to check.
ENOUGH TALK, LET'S SEE THE CODE
Array
const ceos = [
{
name: "Jeff Bezos",
company: "Amazon"
},
{
name: "Mark Zuckerberg",
company: "Facebook"
},
{
name: "Tim Cook",
company: "Apple"
}
];
Function
const arrayIncludesInObj = (arr, key, valueToCheck) => {
return arr.some(value => value[key] === valueToCheck);
}
Call/Usage
const found = arrayIncludesInObj(ceos, "name", "Tim Cook"); // true
const found = arrayIncludesInObj(ceos, "name", "Tim Bezos"); // false
2021 Solution*
Lodash .some (docs) is a clean solution, if you use the _matchesProperty (docs) shorthand:
_.some(VENDORS, ['Name', 'Magenic'])
Explanation
This will iterate through the VENDORS Array looking for an element Object with the Name key having a value of the String 'Magenic'. Once it finds this element, it returns true and stops iterating. If it doesn't find the element after looking through the entire Array, it returns false.
Code snippet
const VENDORS = [{ Name: 'Magenic', ID: 'ABC' }, { Name: 'Microsoft', ID: 'DEF' }];
console.log(_.some(VENDORS, ['Name', 'Magenic'])); // true
<script src="https://cdn.jsdelivr.net/npm/lodash#4.17.20/lodash.min.js"></script>
* Note that this uses the popular lodash library to achieve the simplest/shortest possible solution. I'm offering this as an alternative to the existing vanilla JS solutions, for those who are interested.
You have to loop, there is no way around it.
function seekVendor(vendors, name) {
for (var i=0, l=vendors.length; i<l; i++) {
if (typeof vendors[i] == "object" && vendors[i].Name === name) {
return vendors[i];
}
}
}
Of course you could use a library like linq.js to make this more pleasing:
Enumerable.From(vendors).Where("$.Name == 'Magenic'").First();
(see jsFiddle for a demo)
I doubt that linq.js will be faster than a straight-forward loop, but it certainly is more flexible when things get a little more complicated.
Correct me if i'm wrong..
i could have used forEach method like this,
var found=false;
vendors.forEach(function(item){
if(item.name === "name"){
found=true;
}
});
Nowadays i'm used to it ,because of it simplicity and self explanatory word.
Thank you.
Functions map, filter, find, and similar are slower than the simple loop.
For me they also less readable than the simple loop and harder to debug. Using them looks like a kind of irrational ritual.
Better have something like this:
arrayHelper = {
arrayContainsObject: function (array, object, key){
for (let i = 0; i < array.length; i++){
if (object[key] === array[i][key]){
return true;
}
}
return false;
}
};
And use it like this with given OP example:
vendors = [{
Name: 'Magenic',
ID: 'ABC'
},
{
Name: 'Microsoft',
ID: 'DEF'
}
];
let abcObject = {ID: 'ABC', Name: 'Magenic'};
let isContainObject = arrayHelper.arrayContainsObject(vendors, abcObject, 'ID');
if you're using jquery you can take advantage of grep to create array with all matching objects:
var results = $.grep(vendors, function (e) {
return e.Name == "Magenic";
});
and then use the results array:
for (var i=0, l=results.length; i<l; i++) {
console.log(results[i].ID);
}
You can use lodash. If lodash library is too heavy for your application consider chunking out unnecessary function not used.
let newArray = filter(_this.props.ArrayOne, function(item) {
return find(_this.props.ArrayTwo, {"speciesId": item.speciesId});
});
This is just one way to do this. Another one can be:
var newArray= [];
_.filter(ArrayOne, function(item) {
return AllSpecies.forEach(function(cItem){
if (cItem.speciesId == item.speciesId){
newArray.push(item);
}
})
});
console.log(arr);
The above example can also be rewritten without using any libraries like:
var newArray= [];
ArrayOne.filter(function(item) {
return ArrayTwo.forEach(function(cItem){
if (cItem.speciesId == item.speciesId){
newArray.push(item);
}
})
});
console.log(arr);
Hope my answer helps.
Many answers here are good and pretty easy. But if your array of object is having a fixed set of value then you can use below trick:
Map all the name in a object.
vendors = [
{
Name: 'Magenic',
ID: 'ABC'
},
{
Name: 'Microsoft',
ID: 'DEF'
}
];
var dirtyObj = {}
for(var count=0;count<vendors.length;count++){
dirtyObj[vendors[count].Name] = true //or assign which gives you true.
}
Now this dirtyObj you can use again and again without any loop.
if(dirtyObj[vendor.Name]){
console.log("Hey! I am available.");
}
To compare one object to another, I combine a for in loop (used to loop through objects) and some().
You do not have to worry about an array going out of bounds etc, so that saves some code. Documentation on .some can be found here
var productList = [{id: 'text3'}, {id: 'text2'}, {id: 'text4', product: 'Shampoo'}]; // Example of selected products
var theDatabaseList = [{id: 'text1'}, {id: 'text2'},{id: 'text3'},{id:'text4', product: 'shampoo'}];
var objectsFound = [];
for(let objectNumber in productList){
var currentId = productList[objectNumber].id;
if (theDatabaseList.some(obj => obj.id === currentId)) {
// Do what you need to do with the matching value here
objectsFound.push(currentId);
}
}
console.log(objectsFound);
An alternative way I compare one object to another is to use a nested for loop with Object.keys().length to get the amount of objects in the array. Code below:
var productList = [{id: 'text3'}, {id: 'text2'}, {id: 'text4', product: 'Shampoo'}]; // Example of selected products
var theDatabaseList = [{id: 'text1'}, {id: 'text2'},{id: 'text3'},{id:'text4', product: 'shampoo'}];
var objectsFound = [];
for(var i = 0; i < Object.keys(productList).length; i++){
for(var j = 0; j < Object.keys(theDatabaseList).length; j++){
if(productList[i].id === theDatabaseList[j].id){
objectsFound.push(productList[i].id);
}
}
}
console.log(objectsFound);
To answer your exact question, if are just searching for a value in an object, you can use a single for in loop.
var vendors = [
{
Name: 'Magenic',
ID: 'ABC'
},
{
Name: 'Microsoft',
ID: 'DEF'
}
];
for(var ojectNumbers in vendors){
if(vendors[ojectNumbers].Name === 'Magenic'){
console.log('object contains Magenic');
}
}
Alternatively you can do:
const find = (key, needle) => return !!~vendors.findIndex(v => (v[key] === needle));
var without2 = (arr, args) => arr.filter(v => v.id !== args.id);
Example:
without2([{id:1},{id:1},{id:2}],{id:2})
Result:
without2([{id:1},{id:1},{id:2}],{id:2})
You can try this its work for me.
const _ = require('lodash');
var arr = [
{
name: 'Jack',
id: 1
},
{
name: 'Gabriel',
id: 2
},
{
name: 'John',
id: 3
}
]
function findValue(arr,value) {
return _.filter(arr, function (object) {
return object['name'].toLowerCase().indexOf(value.toLowerCase()) >= 0;
});
}
console.log(findValue(arr,'jack'))
//[ { name: 'Jack', id: 1 } ]
const a = [{one:2},{two:2},{two:4}]
const b = a.filter(val => "two" in val).length;
if (b) {
...
}
I would rather go with regex.
If your code is as follows,
vendors = [
{
Name: 'Magenic',
ID: 'ABC'
},
{
Name: 'Microsoft',
ID: 'DEF'
}
];
I would recommend
/"Name":"Magenic"/.test(JSON.stringify(vendors))