Array manipulations using the reduce method
Wed Apr 17 2024 Sum of Elements in Array:
Implemented a straightforward function to sum all elements in an array, demonstrating reduce as an effective tool for aggregating numerical data.
Prefix Sum Array:
Developed a function to generate a prefix sum array, which provides cumulative sums up to each index, illustrating reduce's capability to build progressively complex arrays from simple lists.
Flatten a Nested Array:
Created a recursive flatten function that handles deeply nested arrays, showcasing how reduce can be adapted for tasks requiring depth handling and recursion.
Group Elements by Age:
Utilized reduce to group objects by a common key (age in this case), forming a hash map where each key points to an array of objects sharing that key, demonstrating its utility in structuring and categorizing data.
Count Occurrences of Elements:
Crafted a function to count the frequency of elements in an array, turning a list of items into a map of counts, which highlights reduce's ability to efficiently transform and summarize data.
1//Sum of Elements in Array
2const numbers = [1, 2, 3, 4, 5];
3
4function sum(arr) {
5 return arr.reduce((acc, item) => {
6 return (acc += item);
7 }, 0);
8}
9console.log(sum(numbers));
10
11//Prefix Sum Array
12let arr = [3, 1, 5, 2, 4];
13
14function prefixSumArray(arr) {
15 let prefArr = arr.reduce(
16 (acc, item) => {
17 return [...acc, acc[acc.length - 1] + item];
18 },
19 [0]
20 );
21 prefArr.shift();
22 return prefArr;
23}
24
25console.log(prefixSumArray(arr));
26
27//Flatten a nested Array
28const nested = [[2, 3], 1, 4, [5, [6, 7]]];
29
30function flatten(arr) {
31 return arr.reduce((acc, item) => {
32 if (Array.isArray(item)) {
33 if (item.length === 0) {
34 return acc;
35 } else {
36 return acc.concat(flatten(item));
37 }
38 } else {
39 acc.push(item);
40 return acc;
41 }
42 }, []);
43}
44
45console.log(flatten(nested));
46
47//Group Eleements by Age
48const people = [
49 {name: 'Alice', age: 25}, {name: 'Bob', age: 30}, {name: 'Charlie', age: 25}
50];
51// Output:
52//{25: [{name: 'Alice', age: 25}, {name: 'Charlie', age: 25}], 30: [{name: 'Bob', age: 30}]}
53function groupByAge(arr){
54 return arr.reduce((acc, item)=>{
55 acc[item.age] = acc[item.age] || [];
56 acc[item.age].push(item);
57 return acc;
58 },{})
59}
60
61console.log(groupByAge(people))
62
63//Count Occurrences of Elements
64const fruitOccur = ['apple', 'banana', 'apple', 'orange', 'banana', 'apple'];
65// Output: {apple: 3, banana: 2, orange: 1}
66
67
68function countOccurrences(arr) {
69 return arr.reduce((acc, item) => {
70 acc[item] = (acc[item] || 0) + 1;
71 return acc;
72 }, {});
73}
74
75console.log(countOccurrences(fruitOccur))