- Write a function which can concatenate 2 arrays. If only one array is passed it will duplicate it
- Write a program to replace 3 center elements of the 1st array by center 3 elements of the 2nd array
- Sort the given array of integers in ascending or descending order
- Sort the given array of objects in ascending order according the authors lastname
- Square all the positive numbers of the array and return the output array
- Write a code to generate an array with range of numbers and shuffle them
- Check if the user with the name "John" exists in the array of objects
- Generate an array of objects with properties id and full name from an array of objects where each object will have id, firstname and lastname
- Write a program to calculate the sum of all the values of an array
- Get the maximum value from a numbers array along with its index
- Find the number of occurences of minimum value in the numbers list
- Create an array of length n with all the values of it set to 10
- Write the code to remove the duplicates from the array
- Design a flat function which flattens an array to any depth
- Check if all the students of have passed or not (40 is the pass marks)
- Get the average of all the salaries which is greater than 10000 from the department of "IT" from the array of objects)
- Extract the list of all the elements from the list of numbers given in 2 arrays
- Get the list of all distinct elements which are present in both list of numbers
- Extract list of elements present only in the first list given.
- Create a function named "average" which can calculate the average of an array and should be available to be called from any Array object.
- Write a code to eliminate duplicate objects in an array where each object has an 'id' property which can be used to identify the object and the duplicate object with lower rank to be removed
- Create an array which will only accept string values. (Homogeneous array of strings)
- Create a Proxy object through which the array can be accessed as usual but also allow to access the values through negative indices
- Function can take 2 arguments which concatenates arrays
- 2nd array parameter can be defaulted to 1st array if the value is not passed
function mergeArray(arr1, arr2 = arr1){
return [...arr1, ...arr2];
}function mergeArray(arr1, arr2 = arr1){
return arr1.concat(...arr2);
}function mergeArray(arr1, arr2 = arr1){
arr1.push(...arr2);
return arr1;
}When 2nd argument is not passed, the case is same as duplicating the array
slicemethod on array can be used to fetch the values of range in the arraysplicemethod on array can be used to replace the value of range in the array
const a = [1, 2, 3, 4, 5];
const b = [4, 0, 0, 0, 8];
const startPositionFor1stArray = a.length / 2 - 1;
const startPositionFor2ndArray = b.length / 2 - 1;
a.splice(startPositionFor1stArray, 3, ...b.slice(startPositionFor2ndArray, startPositionFor2ndArray + 3));The center most 3 values of array 'a' is replaced by 'b'
sortmethod sorts the elements of an array in place and returns the sorted array- It receives a function as an argument, which is used for comparision
arr.sort((a, b)=> a - b); // ascending
arr.sort((a, b)=> b - a); // descendingIf function is not passed an argument, default sorting will happen
// Example
const books = [
{ name: "Harry Potter", author: "Joanne Rowling" },
{ name: "Warcross", author: "Marie Lu" },
{ name: "The Hunger Games", author: "Suzanne Collins" },
]sorttakes a function and expects the return value to be an integer for sorting- The last names of the author can be compared and the result can be returned for sorting
books.sort((book1, book2) => {
const authorLastName1 = book1.author.split(" ")[1];
const authorLastName2 = book2.author.split(" ")[1];
return authorLastName2 > authorLastName1 ? -1 : 1;
});Returning a true or false will not work as the algorithm expects an integer value
filteris the method on Array which can be used to filter. It receives a function which can return boolean to filter the elementsmapis the method on Array which can be used to map the values to new values. It receives a function which can return the modified value
const positiveArr = arr.filter((value) => value >= 0);
const squaredPositiveArr = arr.map((value) => value * value);const squaredPositiveArr = arr.filter((value) => value >= 0).map((value) => value * value);2nd solution uses method chaining where the return value from filter fuction is an array on which map method is being called
- https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter
- https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map
- An array of numbers in the range can be generated from a function which can take start and end value of the range
- The shuffling can be achieved simply by sorting the array using a function which randomly returns positive or negative numbers
- The shuffling of the values can be also done by picking a value from a random index from the current array and moving it in to a new array
function rangeGenFunc(start = 1, end = 0) {
const arr = [];
for (let i = start; i <= end; i++) {
arr.push(i);
}
return arr;
}
const arr = rangeGenFunc(1, 10); // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
arr.sort(() => 0.5 - Math.random()); // [6, 8, 5, 10, 4, 3, 9, 2, 7, 1]function* rangeGen(start = 1, end = 0) {
for (let i = start; i <= end; i++){
yield i;
}
}
let arr = [...rangeGen(1, 10)]; // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
let shuffledArr = [];
const length = arr.length;
for (let i = 0; i < length; i++) {
shuffledArr.push(...arr.splice(Math.floor(Math.random() * arr.length), 1));
}
console.log(shuffledArr) // [5, 4, 7, 10, 3, 6, 8, 2, 1, 9]2nd solution uses generator function to generate the range of values which can be converted to an array by spreading.
const doesJohnExist = arr.some((obj) => obj.name === "John");const jonhObject = arr.find((obj) => obj.name === "John");
const doesJohnExist = jonhObject ? true : false;const jonhIndex = arr.findIndex((obj) => obj.name === "John");
const doesJohnExist = jonhIndex < 0 ? false : true;Generate an array of objects with properties id and full name from an array of objects where each object will have id, firstname and lastname
- To manipulate array of objects
mapmethod can be used
const employeesListWithFullName = arr.map((obj) => { return { id, fullName: obj.firstName + " " + obj.lastName } });- Sum of the values of an array can calculated by iterating and adding all the values of the array
reducemethod of array can be used efficiently to calculate the sum with or without initial value
const sum = arr.reduce((acc, value) => acc + value, 0);const sum = arr.reduce((acc, value) => acc + value);const sum = 0;
for(let value of arr){
sum = sum + value;
}reduce method takes a function as 1st argument and initial value as 2nd argument. The return value of current iteration will be 1st argument for the next iteration along with the next element of the array
Math.maxis a method which returns maximum value from a given list of valuesreducecan also be designed to return the maximum value of each comparision
const max = Math.max(...arr);
arr.indexOf(max); // position of max numberlet max = a[0], position = 0;
for(let index in arr){
if(arr[index] > max){
position = index
max = value;
}
}
position; // position of max numberconst max = arr.reduce((a, b) => a < b ? a : b);
arr.indexOf(max); // position of max numberThough 2nd solution is verbose compared but has good performance
- https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/max
- https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/min
filtermethod can be used to fetch all the minimum values and we can get the count of those valuses
const min = Math.min(...arr);
minArr = arr.filter((value) => value === min);
minArr.length; // count of minimum value occurencesfillis a method on Array prototype which fills all the slots of array with the value given passed as the argument
const n = 5;
const arr = new Array(n);
arr.fill(10);If an object is passed the object reference is copied to all the slots and not the different objects
- Set is a data structure which does not allow duplicate elements
const set = new Set(...arr);
const distinctArr = [...set];- Flat function can be used to flatten the array by recursive call
function flat(arr){
const flatArr = [];
arr.forEach((value) => {
if(Array.isArray(value)){
flatArr.push(...flat(value));
}
else{
flatArr.push(value);
}
});
return flatArr;
}everyis a method on Array prototype which returns true only if all the elements condition satisfies the condition
const isAllPass = students.every((student) => student.marks >= 40);Get the average of all the salaries which is greater than 10000 from the department of "IT" from the array of objects)
const itEmployeesWithSalaryGT10K = employees.filter((employee) => employee.salary > 10000 && employee.dept === 'IT );
const itTotalSalaryGT10K = itEmployeesWithSalaryGT10K.reduce((acc, value) => acc + value, 0);
const itAvgSalaryGT10K = itTotalSalaryGT10K / itEmployeesWithSalaryGT10K.length;- The union array will be the result if all the elements from the 2 arrays are picked
const set1 = new Set(...arr1);
const set2 = new Set(...arr2);
const distinctArr = [...set1, ...set2];- The intersection array will be the result if the common elements from the 2 arrays are picked
const intersectionArr = arr1.filter(value => arr2.includes(value));
const distinctIntersectionArr = [...new Set(intersectionArr)];const set1 = new Set(arr1);
const set2 = new Set(arr2);
const distinctIntersectionArr = [...set1].filter(value => set2.has(value));- The only present elements of 1st list will be the result when all the elements of 1st list not present in the 2nd are chosen
const set1 = new Set(arr1);
const set2 = new Set(arr2);
const intersectionArr = [...set1].filter(value => !set2.has(value));Elements of 2nd list only can be obtained by checking for all the elements of lis 2 which are not present in list1
Create a function named "average" which can calculate the average of an array and should be available to be called from any Array object.
- The function added to Array prototype are accessible to all the objects of Array
Array.prototype.average = function (){
let total = 0;
for(let index in this) {
total += this[index];
}
return total / this.length;
}Write a code to eliminate duplicate objects in an array where each object has an 'id' property which can be used to identify the object and the duplicate object with lower rank to be removed
// Example
const arr = [
{
id: 1,
name: 'emp1',
rank: 4,
},
{
id: 2,
name: 'emp2',
rank: 1,
},
{
id: 2,
name: 'emp2',
rank: 2, // this is a duplicate object (id = 2) and has lower rank
},
{
id: 3,
name: 'emp3',
rank: 3,
},
];- The duplicate objects cannot be removed using
Setas the 2 objects with same structure and data have different references Mapcan be used to have 'id' as the key and object as value- If 'id' is already present in the array, object with the higher rank can be retained
const map = new Map();
arr.forEach(obj => {
if (map.has(obj.id)) {
if (obj.rank < map.get(obj.id).rank) {
map.set(obj.id, obj);
}
} else {
map.set(obj.id, obj);
}
});
distinctArr = [...map.values()];- Array in JavaScript a collection of values of any type by default
- Proxy can be used to validate and insert to the array only if the value satisfies the condition using
settrap
var stringsArr = [];
var stringsArr = new Proxy(stringsArr, {
set(target, prop, receiver){
if(typeof receiver === "string"){
target[target.length] = receiver;
}
return true;
}
});
// driver code
stringsArr.push("Hello", 5, {}, "world", true, [1, 2, 3]);
stringsArr; // ["Hello", "world"]The functionality of the code can be modified to make the array accept any one or more kind of values only
Create a Proxy object through which the array can be accessed as usual but also allow to access the values through negative indices
// Example
let arr = [10, 20, 30];
arr[-1]; // 30
arr[-2]; // 20gettrap of proxy can be used to map the negative index to the valid array position
arr = new Proxy(arr, {
get(target, handler) {
if (handler < 0) return target[target.length + Number(handler)];
else return target[handler];
},
});