I have and array of arrays aa = [['a'], ['b'], ['c']] and i have an array a = ['a', 'b', 'c']
I need to get the item in aa for each element in a i.e i want to list elements in a with their respective arrays in aa the result should be like
a: ['a'] b: ['b'] c: ['c']
I tried this code but it does return the first element i aa for each element in a
I wonder what's wrong here
const aa = [
['a'],
['b'],
['c']
]
const a = ['a', 'b', 'c']
let b = []
a.forEach((el) => {
b.push(
aa.filter((element) => {
return element.includes(el)
})
)
})
console.log(b)
Try this
const aa = [
['a'],
['b'],
['c']
];
const a = ['a', 'b', 'c'];
let b = {};
a.forEach( // loop "a"
aEl => b[aEl] = aa.filter( // filter "aa"
aaEl => aaEl.includes(aEl) // on array that includes the item from 'a'
).flat() // we need to flatten the resulting array before returning it
);
console.log(JSON.stringify(b)); // using stringify to make it readable
Since you want your output to be a key-value list (a: ['a']), variable b should be a map. Let's also rename b to out for readability.
out = {}
To get a better view of if our code is working, let's use some unique test data, and let's rename a to keys and aa to values.
const keys = ['A', 'B', 'C']
const values = [
['A', 'A2', 'a3'],
['B1', 'B', 'b3'],
['C1', 'C2', 'C']
]
For every key in keys, we want to set search for all arrays in values that contain the key. To set the search result to out we use brackets like so:
keys.forEach((key) => {
out[key] = values.filter(valueArr => valueArr.includes(key))
})
This outputs:
{
"A": [["A", "A2", "a3"]],
"B": [["B1", "B", "b3"]],
"C": [["C1", "C2", "C"]]
}
Now there are two arrays around each value. This is because values.filter can return multiple arrays. To combine these into a single array you can use the flat() function. The whole code looks like:
const keys = ['A', 'B', 'C']
const values = [
['A', 'A2', 'a3'],
['B1', 'B', 'b3'],
['C1', 'C2', 'C']
]
out = {}
keys.forEach((key) => {
out[key] = values.filter(valueArr => valueArr.includes(key)).flat()
})
console.log(out)
Say I have the following array:
const array = ['1', '2', '3', '1', '2', '3']
I want to use the following to find the index of '2'
let index = array.findIndex(c => c === '2');
The index would be 1 in this case, but I want to purposely start at index 2 so the result would be 4 instead of 1.
Any thoughts?
const array = ['1', '2', '3', '1', '2', '3'];
let index = array.findIndex(c => c === '2');
console.log(index);
You can use Array.indexOf() and set the fromIndex (2nd param) to 2:
const array = ['1', '2', '3', '1', '2', '3'];
const index = array.indexOf('2', 2);
console.log(index);
If you must use Array.findIndex() (to find an object for example), you can use the 2nd param passed to the callback (the index) to limit the search:
const array = ['1', '2', '3', '1', '2', '3'];
const index = array.findIndex((c, idx) => idx > 1 && c === '2');
console.log(index);
I have below two array:
var val = [['aa', 'ab', 'ac'], ['bb', 'bc', 'bd']];
var key = ['item1', 'item2', 'item3'];
By using any javascript logic I want to get a new array in below format.
[
{item1: 'aa', item2: 'ab', item3: 'ac'},
{item1: 'bb', item2: 'bc', item3: 'bd'}
]
I tried using .forEach and .map() to achieve this, but somehow I couldn't able to do it.
Here is the sample code I tried.https://plnkr.co/edit/oKyjNsBu3wrRin7TaCIb?p=preview
var val = [['aa', 'ab', 'ac'], ['bb', 'bc', 'bd']];
var key = ['item1', 'item2', 'item3'];
var newArr = val.map((elm,i)=>{
return {[key[i]]: elm[i]}
})
console.log('newArr', newArr);
I need the output as below.
[
{item1: 'aa', item2: 'ab', item3: 'ac'},
{item1: 'bb', item2: 'bc', item3: 'bd'}
]
You can use .map() and .reduce() methods to get the desired output:
const vals = [['aa','ab','ac'],['bb','bc','bd']];
const keys = ['item1','item2','item3'];
const result = vals.map((val) => keys.reduce((r, c, i) => (r[c] = val[i], r), {}));
console.log(result);
.as-console-wrapper { max-height: 100% !important; top: 0; }
Map the val array (change its name to allVals for better clarity) to objects using Object.fromEntries:
var allVals = [['aa','ab','ac'],['bb','bc','bd']];
var keys = ['item1','item2','item3'];
const output = allVals.map(vals => Object.fromEntries(
vals.map((val, i) => [keys[i], val])
));
console.log(output);
Using Object.fromEntries():
const values = [['aa','ab','ac'],['bb','bc','bd']];
const keys = ['item1','item2','item3'];
const result = values.map(v => Object.fromEntries(keys.map((k, i) => [k, v[i]])));
console.log(result);
Is there a shorthand way to auto increment a Javascript array like you can in PHP?
PHP Example:
$myArray=[];
$myArray[] = [ 'item1' , 'item2' ];
$myArray[] = [ 'item3' , 'item4' ];
JS Example:
let myArray = [];
myArray[ myArray.length ] = [ 'item1' , 'item2' ];
myArray[ myArray.length ] = [ 'item3' , 'item4 '];
//or
myArray.push( [ 'item1' , 'item2' ] );
myArray.push( [ 'item3' , 'item4' ] );
Without using myArray.length or myArray.push()
Here is the ES6 way, using spread operator
const arr1 = [1,2,3];
const arr2 = [3,4,5];
const arr3 = [...arr1, ...arr2]; // arr3 ==> [1,2,3,3,4,5]
OR
just by using the concat method
const arr1 = [1,2,3];
const arr2 = [3,4,5];
const arr3 = arr1.concat(arr2); // arr3 ==> [1,2,3,3,4,5]
Beside the given answers, you could use Array#splice with a great value for adding the values to the end of the array.
var array = [];
array.splice(Infinity, 0, ...['item1', 'item2']);
array.splice(Infinity, 0, ...['item3', 'item4']);
console.log(array);
There is certainly a way to do exactly the same thing; it even has similar construction:
let arr = ['a', 'b'];
arr = arr.concat([['c', 'd']]);//['a', 'b', ['c', 'd']]
PHP:
<?php
$arr = ["a", "b"];
$arr[] = ["c", "d"];
print_r($arr);
?>
Array
(
[0] => a
[1] => b
[2] => Array
(
[0] => c
[1] => d
)
)
This question already has answers here:
How to get the difference between two arrays in JavaScript?
(84 answers)
Closed 5 months ago.
I am looking for an efficient way to remove all elements from a javascript array if they are present in another array.
// If I have this array:
var myArray = ['a', 'b', 'c', 'd', 'e', 'f', 'g'];
// and this one:
var toRemove = ['b', 'c', 'g'];
I want to operate on myArray to leave it in this state: ['a', 'd', 'e', 'f']
With jQuery, I'm using grep() and inArray(), which works well:
myArray = $.grep(myArray, function(value) {
return $.inArray(value, toRemove) < 0;
});
Is there a pure javascript way to do this without looping and splicing?
Use the Array.filter() method:
myArray = myArray.filter( function( el ) {
return toRemove.indexOf( el ) < 0;
} );
Small improvement, as browser support for Array.includes() has increased:
myArray = myArray.filter( function( el ) {
return !toRemove.includes( el );
} );
Next adaptation using arrow functions:
myArray = myArray.filter( ( el ) => !toRemove.includes( el ) );
ECMAScript 6 sets can permit faster computing of the elements of one array that aren't in the other:
const myArray = ['a', 'b', 'c', 'd', 'e', 'f', 'g'];
const toRemove = new Set(['b', 'c', 'g']);
const difference = myArray.filter( x => !toRemove.has(x) );
console.log(difference); // ["a", "d", "e", "f"]
Since the lookup complexity for the V8 engine browsers use these days is O(1), the time complexity of the whole algorithm is O(n).
var myArray = [
{name: 'deepak', place: 'bangalore'},
{name: 'chirag', place: 'bangalore'},
{name: 'alok', place: 'berhampur'},
{name: 'chandan', place: 'mumbai'}
];
var toRemove = [
{name: 'deepak', place: 'bangalore'},
{name: 'alok', place: 'berhampur'}
];
myArray = myArray.filter(ar => !toRemove.find(rm => (rm.name === ar.name && ar.place === rm.place) ))
The filter method should do the trick:
const myArray = ['a', 'b', 'c', 'd', 'e', 'f', 'g'];
const toRemove = ['b', 'c', 'g'];
// ES5 syntax
const filteredArray = myArray.filter(function(x) {
return toRemove.indexOf(x) < 0;
});
If your toRemove array is large, this sort of lookup pattern can be inefficient. It would be more performant to create a map so that lookups are O(1) rather than O(n).
const toRemoveMap = toRemove.reduce(
function(memo, item) {
memo[item] = memo[item] || true;
return memo;
},
{} // initialize an empty object
);
const filteredArray = myArray.filter(function (x) {
return toRemoveMap[x];
});
// or, if you want to use ES6-style arrow syntax:
const toRemoveMap = toRemove.reduce((memo, item) => ({
...memo,
[item]: true
}), {});
const filteredArray = myArray.filter(x => toRemoveMap[x]);
If you are using an array of objects. Then the below code should do the magic, where an object property will be the criteria to remove duplicate items.
In the below example, duplicates have been removed comparing name of each item.
Try this example. http://jsfiddle.net/deepak7641/zLj133rh/
var myArray = [
{name: 'deepak', place: 'bangalore'},
{name: 'chirag', place: 'bangalore'},
{name: 'alok', place: 'berhampur'},
{name: 'chandan', place: 'mumbai'}
];
var toRemove = [
{name: 'deepak', place: 'bangalore'},
{name: 'alok', place: 'berhampur'}
];
for( var i=myArray.length - 1; i>=0; i--){
for( var j=0; j<toRemove.length; j++){
if(myArray[i] && (myArray[i].name === toRemove[j].name)){
myArray.splice(i, 1);
}
}
}
alert(JSON.stringify(myArray));
Lodash has an utility function for this as well:
https://lodash.com/docs#difference
How about the simplest possible:
var myArray = ['a', 'b', 'c', 'd', 'e', 'f', 'g'];
var toRemove = ['b', 'c', 'g'];
var myArray = myArray.filter((item) => !toRemove.includes(item));
console.log(myArray)
I just implemented as:
Array.prototype.exclude = function(list){
return this.filter(function(el){return list.indexOf(el)<0;})
}
Use as:
myArray.exclude(toRemove);
You can use _.differenceBy from lodash
const myArray = [
{name: 'deepak', place: 'bangalore'},
{name: 'chirag', place: 'bangalore'},
{name: 'alok', place: 'berhampur'},
{name: 'chandan', place: 'mumbai'}
];
const toRemove = [
{name: 'deepak', place: 'bangalore'},
{name: 'alok', place: 'berhampur'}
];
const sorted = _.differenceBy(myArray, toRemove, 'name');
Example code here: CodePen
If you cannot use new ES5 stuff such filter I think you're stuck with two loops:
for( var i =myArray.length - 1; i>=0; i--){
for( var j=0; j<toRemove.length; j++){
if(myArray[i] === toRemove[j]){
myArray.splice(i, 1);
}
}
}
Now in one-liner flavor:
console.log(['a', 'b', 'c', 'd', 'e', 'f', 'g'].filter(x => !~['b', 'c', 'g'].indexOf(x)))
Might not work on old browsers.
This is pretty late but adding this to explain what #mojtaba roohi has answered. The first block of code will not work as each array is having a different object, i.e. df[0] != nfl[2]. Both objects look similar but are altogether different, which is not the case when we use primitive types like numbers.
let df = [ {'name': 'C' },{'name': 'D' }]
let nfl = [ {'name': 'A' },{'name': 'B' },{'name': 'C' },{'name': 'D' }]
let res = nfl.filter(x => df.indexOf(x)<0)
console.log(res)
Here is the working code:
let df = [{'name': 'C' },{'name': 'D' }]
let nfl = [ {'name': 'A' },{'name': 'B' },{'name': 'C' },{'name': 'D' }];
let res = nfl.filter((o1) => !df.some((o2) => o1.name === o2.name));
console.log(res)
If you're using Typescript and want to match on a single property value, this should work based on Craciun Ciprian's answer above.
You could also make this more generic by allowing non-object matching and / or multi-property value matching.
/**
*
* #param arr1 The initial array
* #param arr2 The array to remove
* #param propertyName the key of the object to match on
*/
function differenceByPropVal<T>(arr1: T[], arr2: T[], propertyName: string): T[] {
return arr1.filter(
(a: T): boolean =>
!arr2.find((b: T): boolean => b[propertyName] === a[propertyName])
);
}
Proper way to remove all elements contained in another array is to make source array same object by remove only elements:
Array.prototype.removeContained = function(array) {
var i, results;
i = this.length;
results = [];
while (i--) {
if (array.indexOf(this[i]) !== -1) {
results.push(this.splice(i, 1));
}
}
return results;
};
Or CoffeeScript equivalent:
Array.prototype.removeContained = (array) ->
i = #length
#splice i, 1 while i-- when array.indexOf(#[i]) isnt -1
Testing inside chrome dev tools:
19:33:04.447 a=1
19:33:06.354 b=2
19:33:07.615 c=3
19:33:09.981 arr = [a,b,c]
19:33:16.460 arr1 = arr
19:33:20.317 arr1 === arr
19:33:20.331 true
19:33:43.592 arr.removeContained([a,c])
19:33:52.433 arr === arr1
19:33:52.438 true
Using Angular framework is the best way to keep pointer to source object when you update collections without large amount of watchers and reloads.
I build the logic without using any built-in methods, please let me know any optimization or modifications.
I tested in JS editor it is working fine.
var myArray = [
{name: 'deepak', place: 'bangalore'},
{name: 'alok', place: 'berhampur'},
{name: 'chirag', place: 'bangalore'},
{name: 'chandan', place: 'mumbai'},
];
var toRemove = [
{name: 'chirag', place: 'bangalore'},
{name: 'deepak', place: 'bangalore'},
/*{name: 'chandan', place: 'mumbai'},*/
/*{name: 'alok', place: 'berhampur'},*/
];
var tempArr = [];
for( var i=0 ; i < myArray.length; i++){
for( var j=0; j<toRemove.length; j++){
var toRemoveObj = toRemove[j];
if(myArray[i] && (myArray[i].name === toRemove[j].name)) {
break;
}else if(myArray[i] && (myArray[i].name !== toRemove[j].name)){
var fnd = isExists(tempArr,myArray[i]);
if(!fnd){
var idx = getIdex(toRemove,myArray[i])
if (idx === -1){
tempArr.push(myArray[i]);
}
}
}
}
}
function isExists(source,item){
var isFound = false;
for( var i=0 ; i < source.length; i++){
var obj = source[i];
if(item && obj && obj.name === item.name){
isFound = true;
break;
}
}
return isFound;
}
function getIdex(toRemove,item){
var idex = -1;
for( var i=0 ; i < toRemove.length; i++){
var rObj =toRemove[i];
if(rObj && item && rObj.name === item.name){
idex=i;
break;
}
}
return idex;
}
//Using the new ES6 Syntax
console.log(["a", "b", "c", "d", "e", "f", "g"].filter(el => !["b", "c", "g"].includes(el)));
// OR
// Main array
let myArray = ["a", "b", "c", "d", "e", "f", "g"];
// Array to remove
const toRemove = ["b", "c", "g"];
const diff = () => (myArray = myArray.filter((el) => !toRemove.includes(el)));
console.log(diff()); // [ 'a', 'd', 'e', 'f' ]
// OR
const diff2 = () => {
return myArray = myArray.filter((el) => !toRemove.includes(el));
};
console.log(diff2()); // [ 'a', 'd', 'e', 'f' ]
A High performance and immutable solution
Javascript
const excludeFromArr = (arr, exclude) => {
const excludeMap = exclude.reduce((all, item) => ({ ...all, [item]: true }), {});
return arr.filter((item) => !excludeMap?.[item]);
};
Typescript:
const excludeFromArr = (arr: string[], exclude: string[]): string[] => {
const excludeMap = exclude.reduce<Record<string, boolean>>((all, item) => ({ ...all, [item]: true }), {});
return arr.filter((item) => !excludeMap?.[item]);
};