I was trying to write a algorithm in javascript that returns all the possible 3 digit numbers numbers from a given array of length 6
For Example
var arr = [1, 2, 3, 4, 5, 6];
I have already got the combinations with the same sets of numbers in different positions in the 2D array.
(The code which I took the help of)
If I have the same numbers in different combinations then I would like to remove them form the array. like I have [1, 2, 3] at index i in the array comtaining all the possible combinations then I would like to remove other combination with the same numbers like [2, 1, 3], [1, 3, 2] and so on..
Note the array also contains numbers repeated like [3, 3, 3], [2, 2, 2], [3, 2, 3] and so on
I expect an 2d array which has the values : [[1,2,3],[1,2,4],[1,2,5],[1,2,6],[1,3,4]] and so on (24 possibilities)
Is there any way to do this?
Extending the answer you linked, just filter out the results with the help of a Set.
Sort an individual result, convert them into a String using join(), check if it's present in set or not, and if not, then store them in the final result.
function cartesian_product(xs, ys) {
var result = [];
for (var i = 0; i < xs.length; i++) {
for (var j = 0; j < ys.length; j++) {
// transform [ [1, 2], 3 ] => [ 1, 2, 3 ] and append it to result []
result.push([].concat.apply([], [xs[i], ys[j]]));
}
}
return result;
}
function cartesian_power(xs, n) {
var result = xs;
for (var i = 1; i < n; i++) {
result = cartesian_product(result, xs)
}
return result;
}
function unique_cartesian_power(xs, n) {
var result = cartesian_power(xs, n);
var unique_result = [];
const set = new Set();
result.forEach(function(value) {
var representation = value.sort().join(' ');
if (!set.has(representation)) {
set.add(representation);
unique_result.push(value);
}
});
return unique_result;
}
console.log(unique_cartesian_power([1, 2, 3, 4, 5, 6], 3));
const arr = [1, 2, 3, 4, 5, 6];
const result = arr.reduce((a, v) => arr.reduce((a, v2) => {
arr.reduce((a, v3) => {
const current = [v, v2, v3].sort().join(",");
!a.find(_ => _.sort().join() === current) && a.push([v, v2, v3]);
return a;
}, a);
return a;
}, a), []);
console.log(result.length);
console.log(...result.map(JSON.stringify));
You could take an iterative and recursive approach by sorting the index and a temporary array for the collected values.
Because of the nature of going upwards with the index, no duplicate set is created.
function getCombination(array, length) {
function iter(index, right) {
if (right.length === length) return result.push(right);
if (index === array.length) return;
for (let i = index, l = array.length - length + right.length + 1; i < l; i++) {
iter(i + 1, [...right, array[i]]);
}
}
var result = [];
iter(0, []);
return result;
}
var array = [1, 2, 3, 4, 5, 6],
result = getCombination(array, 3);
console.log(result.length);
result.forEach(a => console.log(...a));
.as-console-wrapper { max-height: 100% !important; top: 0; }
This is a good example, that it is usually worthwhile not asking for a specific answer for a generic problem shown with a specific question; however as you've requested - if you really have the above constraints which kind of don't make much sense to me, you could do it like that:
function combine(firstDigits, secondDigits, thirdDigits) {
let result = [];
firstDigits.forEach(firstDigit => {
// combine with all secondDigitPermutations
secondDigits.forEach(secondDigit => {
// combine with all thirdDigitPermutations
thirdDigits.forEach(thirdDigit => {
result.push([firstDigit, secondDigit, thirdDigit])
})
})
});
// now we have all permutations and simply need to filter them
// [1,2,3] is the same as [2,3,1]; so we need to sort them
// and check them for equality (by using a hash) and memoize them
// [1,2,3] => '123'
function hashCombination(combination) {
return combination.join('ಠ_ಠ');
}
return result
// sort individual combinations to make them equal
.map(combination => combination.sort())
.reduce((acc, currentCombination) => {
// transform the currentCombination into a "hash"
let hash = hashCombination(currentCombination);
// and look it up; if it is not there, add it to cache and result
if (!(hash in acc.cache)) {
acc.cache[hash] = true;
acc.result.push(currentCombination);
}
return acc;
}, {result: [], cache: {}})
.result;
}
console.log(combine([1,2,3,4,5,6],[1,2,3,4,5,6],[1,2,3,4,5,6]).length);
console.log(...combine([1,2,3,4,5,6],[1,2,3,4,5,6],[1,2,3,4,5,6]).map(JSON.stringify));
This does not include some super-clever assumptions about some index, but it does abuse the fact, that it's all about numbers. It is deliberately using no recursion, because this would easily explode, if the amount of combinations is going to be bigger and because recursion in itself is not very readable.
For a real world problem™ - you'd employ a somewhat similar strategy though; generating all combinations and then filter them. Doing both at the same time, is an exercise left for the astute reader. For finding combinations, that look different, but are considered to be the same you'd also use some kind of hashing and memoizing.
let arr1 = [1,2,3,4,5,6];
function getCombination(arr){
let arr2 = [];
for(let i=0; i<arr.length; i++){
for(let j=i; j<arr.length; j++){
for(let k=j; k<arr.length; k++){
arr2.push([arr[i],arr[j],arr[k]]);
}
}
}
return arr2;
}
console.log(getCombination(arr1));
function destroyer(arr) {
// Remove all the values
var toFilter;
var toFrom;
for(var i=0;i<arguments.length;i++) {
if (typeof arguments[i]=="object") {
toFilter = arguments[i];
} else {
toFrom = arguments[i];
}
}
var result = toFilter.filter(function(value,index,array) {
if(value===toFrom) {
return true;
}
return result;
});
console.log(result);
}
destroyer([1, 2, 3, 1, 2, 3], 2, 3); // it should return [1,1]
It's almost been more than one week that i'm trying to solve this algorithm. In this task we need to remove the arguments value present in the initial array, they have mentioned to solve this by using arguments and filter method. Well i know what filter and arguments does in Javascript and i solved the previous algorithm using filter method and i read about arguments and it's use but never used it before. Every time i did something using these two it gave me a blank array. Please can anyone help me how can we do this using filter and arguments ?
Just my idea, you can modify it the way you want:
function isValid() {
return value != 2 && value != 3;
}
var arr = [1, 2, 3, 1, 2, 3];
arr.filter(isValid); //It should return [1,1];
What you need now is to get 2 and 3 value from arguments object and change isValid function.
There are several problems, let's list them one by one:
You overwrite toFrom, so instead of your intention to get ALL non-objects (i.e. 2 & 3), you only get the last non-object (i.e. 3)
In filter(), return true means "Keep this element in the list", and you return true if the value is equal to toFrom = 3
The verb solve does not work with the noun algorithm. Because algorithm is the way to solve a problem
I didn't try but I guess your code will output [3,3], so if you want to output [1,1], try following modified code based on your version:
function destroyer(arr) {
// Remove all the values
var toFilter;
var toFrom = [];
for(var i=0;i<arguments.length;i++) {
if (typeof arguments[i]=="object") {
toFilter = arguments[i];
} else {
// maintain a list of ALL non-objects which to be filtered
toFrom.push(arguments[i]);
}
}
var result = toFilter.filter(function(value,index,array) {
if(toFrom.indexOf(value) != -1) {
// If element is in the toFrom list, DO NOT keep it
return false;
}
return true;
});
console.log(result);
}
destroyer([1, 2, 3, 1, 2, 3], 2, 3); // it should return
or you may try my version :)
function destroyer(arr) {
// Remove all the values
for(var i=0;i<arguments.length;i++) {
arr = arr.filter( x => x !== arguments[i]);
}
console.log(arr);
}
destroyer([1, 2, 3, 1, 2, 3], 2, 3); // it should return
What you can do is construct a lookup of the values that you want to remove from the array, and then filter the original array by returning values that do not exist in the lookup:
function destroyer(arr) {
var lookup = {};
// For each remaining argument, add it to the lookup.
for (var i = 0; i < arguments.length; i++) {
lookup[arguments[i]] = true;
}
// Filter the array and return a new array
// with elements that don't exist in the lookup.
return arr.filter(function(elem) {
return typeof lookup[elem] === 'undefined';
});
}
console.log(destroyer([1, 2, 3, 1, 2, 3], 2, 3)); //it should return [1,1]
I am trying to figure out a solution for symmetric
difference using javascript that accomplishes the following
objectives:
accepts an unspecified number of arrays as arguments
preserves the original order of the numbers in the arrays
does not remove duplicates of numbers in single arrays
removes duplicates occurring across arrays
Thus, for example,
if the input is ([1, 1, 2, 6], [2, 3, 5], [2, 3, 4]),
the solution would be, [1, 1, 6, 5, 4].
I am trying to solve this as challenge given by an online
coding community. The exact instructions of the challenge
state,
Create a function that takes two or more arrays and returns an array
of the symmetric difference of the provided arrays.
The mathematical term symmetric difference refers to the elements in
two sets that are in either the first or second set, but not in both.
Although my solution below finds the numbers that are
unique to each array, it eliminates all numbers occuring
more than once and does not keep the order of the numbers.
My question is very close to the one asked at finding symmetric difference/unique elements in multiple arrays in javascript. However, the solution
does not preserve the original order of the numbers and does not preserve duplicates of unique numbers occurring in single arrays.
function sym(args){
var arr = [];
var result = [];
var units;
var index = {};
for(var i in arguments){
units = arguments[i];
for(var j = 0; j < units.length; j++){
arr.push(units[j]);
}
}
arr.forEach(function(a){
if(!index[a]){
index[a] = 0;
}
index[a]++;
});
for(var l in index){
if(index[l] === 1){
result.push(+l);
}
}
return result;
}
symsym([1, 1, 2, 6], [2, 3, 5], [2, 3, 4]); // => Desired answer: [1, 1, 6. 5. 4]
As with all problems, it's best to start off writing an algorithm:
Concatenate versions of the arrays, where each array is filtered to contain those elements which no array other than the current one contains
Then just write that down in JS:
function sym() {
var arrays = [].slice.apply(arguments);
return [].concat.apply([], // concatenate
arrays.map( // versions of the arrays
function(array, i) { // where each array
return array.filter( // is filtered to contain
function(elt) { // those elements which
return !arrays.some( // no array
function(a, j) { //
return i !== j // other than the current one
&& a.indexOf(elt) >= 0 // contains
;
}
);
}
);
}
)
);
}
Non-commented version, written more succinctly using ES6:
function sym(...arrays) {
return [].concat(arrays .
map((array, i) => array .
filter(elt => !arrays .
some((a, j) => i !== j && a.indexOf(elt) >= 0))));
}
Here's a version that uses the Set object to make for faster lookup. Here's the basic logic:
It puts each array passed as an argument into a separate Set object (to faciliate fast lookup).
Then, it iterates each passed in array and compares it to the other Set objects (the ones not made from the array being iterated).
If the item is not found in any of the other Sets, then it is added to the result.
So, it starts with the first array [1, 1, 2, 6]. Since 1 is not found in either of the other arrays, each of the first two 1 values are added to the result. Then 2 is found in the second set so it is not added to the result. Then 6 is not found in either of the other two sets so it is added to the result. The same process repeats for the second array [2, 3, 5] where 2 and 3 are found in other Sets, but 5 is not so 5 is added to the result. And, for the last array, only 4 is not found in the other Sets. So, the final result is [1,1,6,5,4].
The Set objects are used for convenience and performance. One could use .indexOf() to look them up in each array or one could make your own Set-like lookup with a plain object if you didn't want to rely on the Set object. There's also a partial polyfill for the Set object that would work here in this answer.
function symDiff() {
var sets = [], result = [];
// make copy of arguments into an array
var args = Array.prototype.slice.call(arguments, 0);
// put each array into a set for easy lookup
args.forEach(function(arr) {
sets.push(new Set(arr));
});
// now see which elements in each array are unique
// e.g. not contained in the other sets
args.forEach(function(array, arrayIndex) {
// iterate each item in the array
array.forEach(function(item) {
var found = false;
// iterate each set (use a plain for loop so it's easier to break)
for (var setIndex = 0; setIndex < sets.length; setIndex++) {
// skip the set from our own array
if (setIndex !== arrayIndex) {
if (sets[setIndex].has(item)) {
// if the set has this item
found = true;
break;
}
}
}
if (!found) {
result.push(item);
}
});
});
return result;
}
var r = symDiff([1, 1, 2, 6], [2, 3, 5], [2, 3, 4]);
log(r);
function log(x) {
var d = document.createElement("div");
d.textContent = JSON.stringify(x);
document.body.appendChild(d);
}
One key part of this code is how it compares a given item to the Sets from the other arrays. It just iterates through the list of Set objects, but it skips the Set object that has the same index in the array as the array being iterated. That skips the Set made from this array so it's only looking for items that exist in other arrays. That allows it to retain duplicates that occur in only one array.
Here's a version that uses the Set object if it's present, but inserts a teeny replacement if not (so this will work in more older browsers):
function symDiff() {
var sets = [], result = [], LocalSet;
if (typeof Set === "function") {
try {
// test to see if constructor supports iterable arg
var temp = new Set([1,2,3]);
if (temp.size === 3) {
LocalSet = Set;
}
} catch(e) {}
}
if (!LocalSet) {
// use teeny polyfill for Set
LocalSet = function(arr) {
this.has = function(item) {
return arr.indexOf(item) !== -1;
}
}
}
// make copy of arguments into an array
var args = Array.prototype.slice.call(arguments, 0);
// put each array into a set for easy lookup
args.forEach(function(arr) {
sets.push(new LocalSet(arr));
});
// now see which elements in each array are unique
// e.g. not contained in the other sets
args.forEach(function(array, arrayIndex) {
// iterate each item in the array
array.forEach(function(item) {
var found = false;
// iterate each set (use a plain for loop so it's easier to break)
for (var setIndex = 0; setIndex < sets.length; setIndex++) {
// skip the set from our own array
if (setIndex !== arrayIndex) {
if (sets[setIndex].has(item)) {
// if the set has this item
found = true;
break;
}
}
}
if (!found) {
result.push(item);
}
});
});
return result;
}
var r = symDiff([1, 1, 2, 6], [2, 3, 5], [2, 3, 4]);
log(r);
function log(x) {
var d = document.createElement("div");
d.textContent = JSON.stringify(x);
document.body.appendChild(d);
}
I came across this question in my research of the same coding challenge on FCC. I was able to solve it using for and while loops, but had some trouble solving using the recommended Array.reduce(). After learning a ton about .reduce and other array methods, I thought I'd share my solutions as well.
This is the first way I solved it, without using .reduce.
function sym() {
var arrays = [].slice.call(arguments);
function diff(arr1, arr2) {
var arr = [];
arr1.forEach(function(v) {
if ( !~arr2.indexOf(v) && !~arr.indexOf(v) ) {
arr.push( v );
}
});
arr2.forEach(function(v) {
if ( !~arr1.indexOf(v) && !~arr.indexOf(v) ) {
arr.push( v );
}
});
return arr;
}
var result = diff(arrays.shift(), arrays.shift());
while (arrays.length > 0) {
result = diff(result, arrays.shift());
}
return result;
}
After learning and trying various method combinations, I came up with this that I think is pretty succinct and readable.
function sym() {
var arrays = [].slice.call(arguments);
function diff(arr1, arr2) {
return arr1.filter(function (v) {
return !~arr2.indexOf(v);
});
}
return arrays.reduce(function (accArr, curArr) {
return [].concat( diff(accArr, curArr), diff(curArr, accArr) )
.filter(function (v, i, self) { return self.indexOf(v) === i; });
});
}
That last .filter line I thought was pretty cool to dedup an array. I found it here, but modified it to use the 3rd callback parameter instead of the named array due to the method chaining.
This challenge was a lot of fun!
// Set difference, a.k.a. relative compliment
const diff = (a, b) => a.filter(v => !b.includes(v))
const symDiff = (first, ...rest) =>
rest.reduce(
(acc, x) => [
...diff(acc, x),
...diff(x, acc),
],
first,
)
/* - - - */
console.log(symDiff([1, 3], ['Saluton', 3])) // [1, 'Saluton']
console.log(symDiff([1, 3], [2, 3], [2, 8, 5])) // [1, 8, 5]
Just use _.xor or copy lodash code.
Another simple, yet readable solution:
/*
This filters arr1 and arr2 from elements which are in both arrays
and returns concatenated results from filtering.
*/
function symDiffArray(arr1, arr2) {
return arr1.filter(elem => !arr2.includes(elem))
.concat(arr2.filter(elem => !arr1.includes(elem)));
}
/*
Add and use this if you want to filter more than two arrays at a time.
*/
function symDiffArrays(...arrays) {
return arrays.reduce(symDiffArray, []);
}
console.log(symDiffArray([1, 3], ['Saluton', 3])); // [1, 'Saluton']
console.log(symDiffArrays([1, 3], [2, 3], [2, 8, 5])); // [1, 8, 5]
Used functions: Array.prototype.filter() | Array.prototype.reduce() | Array.prototype.includes()
function sym(arr1, arr2, ...rest) {
//creating a array which has unique numbers from both the arrays
const union = [...new Set([...arr1,...arr2])];
// finding the Symmetric Difference between those two arrays
const diff = union.filter((num)=> !(arr1.includes(num) && arr2.includes(num)))
//if there are more than 2 arrays
if(rest.length){
// recurrsively call till rest become 0
// i.e. diff of 1,2 will be the first parameter so every recurrsive call will reduce // the arrays till diff between all of them are calculated.
return sym(diff, rest[0], ...rest.slice(1))
}
return diff
}
Create a Map with a count of all unique values (across arrays). Then concat all arrays, and filter non unique values using the Map.
const symsym = (...args) => {
// create a Map from the unique value of each array
const m = args.reduce((r, a) => {
// get unique values of array, and add to Map
new Set(a).forEach((n) => r.set(n, (r.get(n) || 0) + 1));
return r;
}, new Map());
// combine all arrays
return [].concat(...args)
// remove all items that appear more than once in the map
.filter((n) => m.get(n) === 1);
};
console.log(symsym([1, 1, 2, 6], [2, 3, 5], [2, 3, 4])); // => Desired answer: [1, 1, 6, 5, 4]
This is the JS code using higher order functions
function sym(args) {
var output;
output = [].slice.apply(arguments).reduce(function(previous, current) {
current.filter(function(value, index, self) { //for unique
return self.indexOf(value) === index;
}).map(function(element) { //pushing array
var loc = previous.indexOf(element);
a = [loc !== -1 ? previous.splice(loc, 1) : previous.push(element)];
});
return previous;
}, []);
document.write(output);
return output;
}
sym([1, 2, 3], [5, 2, 1, 4]);
And it would return the output as: [3,5,4]
Pure javascript solution.
function diff(arr1, arr2) {
var arr3= [];
for(var i = 0; i < arr1.length; i++ ){
var unique = true;
for(var j=0; j < arr2.length; j++){
if(arr1[i] == arr2[j]){
unique = false;
break;
}
}
if(unique){
arr3.push(arr1[i]);}
}
return arr3;
}
function symDiff(arr1, arr2){
return diff(arr1,arr2).concat(diff(arr2,arr1));
}
symDiff([1, "calf", 3, "piglet"], [7, "filly"])
//[1, "calf", 3, "piglet", 7, "filly"]
My short solution. At the end, I removed duplicates by filter().
function sym() {
var args = Array.prototype.slice.call(arguments);
var almost = args.reduce(function(a,b){
return b.filter(function(i) {return a.indexOf(i) < 0;})
.concat(a.filter(function(i){return b.indexOf(i)<0;}));
});
return almost.filter(function(el, pos){return almost.indexOf(el) == pos;});
}
sym([1, 1, 2, 5], [2, 2, 3, 5], [3, 4, 5, 5]);
//Result: [4,5,1]
function sym(args) {
var initialArray = Array.prototype.slice.call(arguments);
var combinedTotalArray = initialArray.reduce(symDiff);
// Iterate each element in array, find values not present in other array and push values in combinedDualArray if value is not there already
// Repeat for the other array (change roles)
function symDiff(arrayOne, arrayTwo){
var combinedDualArray = [];
arrayOne.forEach(function(el, i){
if(!arrayTwo.includes(el) && !combinedDualArray.includes(el)){
combinedDualArray.push(el);
}
});
arrayTwo.forEach(function(el, i){
if(!arrayOne.includes(el) && !combinedDualArray.includes(el)){
combinedDualArray.push(el);
}
});
combinedDualArray.sort();
return combinedDualArray;
}
return combinedTotalArray;
}
console.log(sym([1, 1, 2, 5], [2, 2, 3, 5], [3, 4, 5, 5]));
This function removes duplicates because the original concept of symmetric difference operates over sets. In this example, the function operates on the sets this way: ((A △ B) △ C) △ D ...
function sym(...args) {
return args.reduce((old, cur) => {
let oldSet = [...new Set(old)]
let curSet = [...new Set(cur)]
return [
...oldSet.filter(i => !curSet.includes(i)),
...curSet.filter(i => !oldSet.includes(i))
]
})
}
// Running> sym([1, 1, 2, 6], [2, 3, 5], [2, 3, 4])
console.log(sym([1, 1, 2, 6], [2, 3, 5], [2, 3, 4]))
// Return> [1, 6, 5, 2, 4]
This works for me:
function sym() {
var args = [].slice.call(arguments);
var getSym = function(arr1, arr2) {
return arr1.filter(function(each, idx) {
return arr2.indexOf(each) === -1 && arr1.indexOf(each, idx + 1) === -1;
}).concat(arr2.filter(function(each, idx) {
return arr1.indexOf(each) === -1 && arr2.indexOf(each, idx + 1) === -1;
}));
};
var result = getSym(args[0], args[1]);
var len = args.length - 1, i = 2;
while (--len) {
result = [].concat(getSym(result, args[i]));
i++;
}
return result;
}
console.info(sym([1, 1, 2, 5], [2, 2, 3, 5], [6, 8], [7, 8], [9]));
Alternative: Use the lookup inside a map instead of an array
function sym(...vs){
var has = {};
//flatten values
vs.reduce((a,b)=>a.concat(b)).
//if element does not exist add it (value==1)
//or mark it as multiply found value > 1
forEach(value=>{has[value] = (has[value]||0)+1});
return Object.keys(has).filter(x=>has[x]==1).map(x=>parseInt(x,10));
}
console.log(sym([1, 2, 3], [5, 2, 1, 4],[5,7], [5]));//[3,4,7])
Hey if anyone is interested this is my solution:
function sym (...args) {
let fileteredArgs = [];
let symDiff = [];
args.map(arrayEl =>
fileteredArgs.push(arrayEl.filter((el, key) =>
arrayEl.indexOf(el) === key
)
)
);
fileteredArgs.map(elArr => {
elArr.map(el => {
let index = symDiff.indexOf(el);
if (index === -1) {
symDiff.push(el);
} else {
symDiff.splice(index, 1);
}
});
});
return (symDiff);
}
console.log(sym([1, 2, 3, 3], [5, 2, 1, 4]));
Here is the solution
let a=[1, 1, 2, 6]
let b=[2, 3, 5];
let c= [2, 3, 4]
let result=[...a,...b].filter(item=>!(a.includes(item) && b.includes(item) ))
result=[...result,...c].filter(item=>!(b.includes(item) && c.includes(item) ))
console.log(result) //[1, 1, 6, 5, 4]
Concise solution using
Arrow functions
Array spread syntax
Array filter
Array reduce
Set
Rest parameters
Implicit return
const symPair = (a, b) =>
[...a.filter(item => !b.includes(item)),
...b.filter(item => !a.includes(item))]
const sym = (...args) => [...new Set(args.reduce(symPair))]
The function symPair works for two input arrays, and the function sym works for two or more arrays, using symPair as a reducer.
const symPair = (a, b) =>
[...a.filter(item => !b.includes(item)),
...b.filter(item => !a.includes(item))]
const sym = (...args) => [...new Set(args.reduce(symPair))]
console.log(sym([1, 2, 3], [2, 3, 4], [6]))
const removeDuplicates = (data) => Array.from(new Set(data));
const getSymmetric = (data) => (val) => data.indexOf(val) === data.lastIndexOf(val)
function sym(...args) {
let joined = [];
args.forEach((arr) => {
joined = joined.concat(removeDuplicates(arr));
joined = joined.filter(getSymmetric(joined))
});
return joined;
}
console.log(sym([1, 2, 3], [5, 2, 1, 4]));
Below code worked fine all the scenarios. Try the below code
function sym() {
var result = [];
for (var i = 0; i < arguments.length; i++) {
if (i == 0) {
var setA = arguments[i].filter((val) => !arguments[i + 1].includes(val));
var setB = arguments[i + 1].filter((val) => !arguments[i].includes(val));
result = [...setA, ...setB];
i = i + 1;
} else {
var setA = arguments[i].filter((val) => !result.includes(val));
var setB = result.filter((val) => !arguments[i].includes(val));
result = [...setA, ...setB];
}
}
return result.filter((c, index) => {
return result.indexOf(c) === index;
}).sort();
}
My code passed all test cases for the similar question on freecodecamp. Below is code for the same.
function sym(...args) {
const result = args.reduce((acc, curr, i) => {
if (curr.length > acc.length) {
const arr = curr.reduce((a, c, i) => {
if(a.includes(c)){
}
if (!acc.includes(c) && !a.includes(c)) {
a.push(c);
}
if (!curr.includes(acc[i]) && i < acc.length) {
a.push(acc[i])
}
return a;
}, []);
return [...arr];
} else {
const arr = acc.reduce((a, c, i) => {
if(a.includes(c)){
}
if (!curr.includes(c) && !a.includes(c)) {
a.push(c);
}
if (!acc.includes(curr[i]) && i < curr.length) {
a.push(curr[i])
}
return a;
}, []);
return [...arr]
}
});
let ans = new Set([...result])
return [...ans]
}
sym([1,2,3,3],[5, 2, 1, 4,5]);
I was wondering how I'd go about implementing a method in javascript that removes all elements of an array that clear a certain condition. (Preferably without using jQuery)
Ex.
ar = [ 1, 2, 3, 4 ];
ar.removeIf( function(item, idx) {
return item > 3;
});
The above would go through each item in the array and remove all those that return true for the condition (in the example, item > 3).
I'm just starting out in javascript and was wondering if anyone knew of a short efficient way to get this done.
--update--
It would also be great if the condition could work on object properties as well.
Ex.
ar = [ {num:1, str:"a"}, {num:2, str:"b"}, {num:3, str:"c"} ];
ar.removeIf( function(item, idx) {
return item.str == "c";
});
Where the item would be removed if item.str == "c"
--update2--
It would be nice if index conditions could work as well.
Ex.
ar = [ {num:1, str:"a"}, {num:2, str:"b"}, {num:3, str:"c"} ];
ar.removeIf( function(item, idx) {
return idx == 2;
});
You can use Array filter method.
The code would look like this:
ar = [1, 2, 3, 4];
ar = ar.filter(item => !(item > 3));
console.log(ar) // [1, 2, 3]
You could add your own method to Array that does something similar, if filter does not work for you.
Array.prototype.removeIf = function(callback) {
var i = 0;
while (i < this.length) {
if (callback(this[i], i)) {
this.splice(i, 1);
}
else {
++i;
}
}
};
To me, that's one of the coolest features of JavaScript. Ian pointed out a more efficient way to do the same thing. Considering that it's JavaScript, every bit helps:
Array.prototype.removeIf = function(callback) {
var i = this.length;
while (i--) {
if (callback(this[i], i)) {
this.splice(i, 1);
}
}
};
This avoids the need to even worry about the updating length or catching the next item, as you work your way left rather than right.
You can use Array.filter(), which does the opposite:
ar.filter(function(item, idx) {
return item <= 3;
});
You can use lodash.remove
var array = [1, 2, 3, 4];
var evens = _.remove(array, function(n) {
return n % 2 == 0;
});
console.log(array);
// => [1, 3]
console.log(evens);
// => [2, 4]
Make it a one-liner with arrow function:
ar = ar.filter(i => i > 3);
simply write the following example if condition could work on object properties as well
var ar = [ {num:1, str:"a"}, {num:2, str:"b"}, {num:3, str:"c"} ];
var newArray = [];
for (var i = 0, len = ar.length; i<len; i++) {
if (ar[i].str == "b")
{newArray.push(ar[i]);};
};
console.log(newArray);
See the example Live Example
if you need to remove exactly one item, and you know for sure that the item exists, you can use this one-liner:
ar.splice(ar.findIndex(el => el.id === ID_TO_REMOVE), 1);
// or with custom method:
let ar = [ {id:1, str:"a"}, {id:2, str:"b"}, {id:3, str:"c"}, {id:4,str:"d"} ];
ar.removeById = id => ar.splice(ar.findIndex(el => el.id === id), 1);
ar.removeById(ID_TO_REMOVE);
http://jsfiddle.net/oriadam/72kgprw5/
ES6 only
I love these kinds of questions and just a different version from me too... :)
Array.prototype.removeIf = function(expression) {
var res = [];
for(var idx=0; idx<this.length; idx++)
{
var currentItem = this[idx];
if(!expression(currentItem))
{
res.push(currentItem);
}
}
return res;
}
ar = [ 1, 2, 3, 4 ];
var result = ar.removeIf(expCallBack);
console.log(result);
function expCallBack(item)
{
return item > 3;
}
My solution for an array of numbers would be:
ar = ar.filter(item => item < 4);
For the in-place remove, my solution is
ar.filter(item => !(item > 3))
.forEach(obsoleteItem => ar.splice(ar.indexOf(obsoleteItem), 1));
Incorrect way
First of all, any answer that suggests to use filter does not actually remove the item. Here is a quick test:
var numbers = [1, 2, 2, 3];
numbers.filter(x => x === 2);
console.log(numbers.length);
In the above, the numbers array will stay intact (nothing will be removed). The filter method returns a new array with all the elements that satisfy the condition x === 2 but the original array is left intact.
Sure you can do this:
var numbers = [1, 2, 2, 3];
numbers = numbers.filter(x => x === 2);
console.log(numbers.length);
But that is simply assigning a new array to numbers.
Correct way to remove items from array
One of the correct ways, there are more than 1, is to do it as following. Please keep in mind, the example here intentionally has duplicated items so the removal of duplicates can be taken into consideration.
var numbers = [1, 2, 2, 3];
// Find all items you wish to remove
// If array has objects, then change condition to x.someProperty === someValue
var numbersToRemove = numbers.filter(x => x === 2);
// Now remove them
numbersToRemove.forEach(x => numbers.splice(numbers.findIndex(n => n === x), 1));
// Now check (this is obviously just to test)
console.log(numbers.length);
console.log(numbers);
Now you will notice length returns 2 indicating only numbers 1 and 3 are remaining in the array.