I am interested in tallying up the number of adjacent matching elements within an array and then providing the final count

Question

I am interested in tallying up the number of adjacent matching elements within an array and then providing the final count

I have an array and want to find all neighboring matches, count them, and then return the count. This needs to be done in a loop using .map() so that I don't need to store memory of what was counted beyond the current element. The number of current elements will be used to reserve enough spaces for each group of elements.

array = [ball, batter, batter, amount, amount, github, github, github, account, account, account, account, account, account, account, github, github, github]

An example of the desired results from this array would be: on the first loop it would return 1, second loop would return 2, then 2, then 3, then 7, then 3

This count will serve as a variable to reserve space like so:

number to reserve: count

Through each loop, the variable count will be updated with the current elements count. The counting loop will not stop until the next element does not match the current element, and the variable count will only be available once all consecutive matches are found. Therefore, if I put console.log(count) at the end of the function, I would get each number output individually.

javascript arrays loops sorting

Answer 1

Answer №1

To easily determine the consecutive strings in an array, you can follow this method:

const array = ["ball", "batter", "batter", "amount", "amount", "github", "github", "github", "account", "account", "account", "account", "account", "account", "account", "github", "github", "github"]

const result = [];
let last = array[0], lastSameIndex = 0;
for (let i = 1; i < array.length; ++i) {
  if (array[i] !== last) {
    result.push(i - lastSameIndex);
    lastSameIndex = i;
    last = array[i];
  }
}
result.push(array.length - lastSameIndex);

console.log(result);

Let's start with some initial values such as

last = array[0], which means last = "ball", and lastSameIndex = 0

We will begin from index 1 and focus on a scenario where two elements are not equal i.e. array[i] !== last. In such cases, we need to add the count of the same element encountered so far like this:

result.push(i - lastSameIndex);

After that, update the value and index to mark the new element that needs to be counted again.

lastSameIndex = i;
last = array[i];

Additionally, handling the case when the loop reaches its end is important. Here, we push the count of the last element that was being counted from the start or lastSameIndex until the end of the array.

result.push(array.length - lastSameIndex);

Second approach

const array = [ "ball", "batter", "batter", "amount", "amount", "github", "github", "github", "account", "account", "account", "account", "account", "account", "account", "github", "github", "github"];

let lastStr = "",
  num = 0;
const result = array
  .map((s) => {
    if (lastStr !== s) {
      lastStr = s;
      num = num === 0 ? 1 : 0;
    }
    return num;
  })
  .join("")
  .match(/(\d)\1*/g)
  .map((s) => s.length);
  
console.log(result);

Answer 2

To easily determine the consecutive strings in an array, you can follow this method:

const array = ["ball", "batter", "batter", "amount", "amount", "github", "github", "github", "account", "account", "account", "account", "account", "account", "account", "github", "github", "github"]

const result = [];
let last = array[0], lastSameIndex = 0;
for (let i = 1; i < array.length; ++i) {
  if (array[i] !== last) {
    result.push(i - lastSameIndex);
    lastSameIndex = i;
    last = array[i];
  }
}
result.push(array.length - lastSameIndex);

console.log(result);

Let's start with some initial values such as

last = array[0], which means last = "ball", and lastSameIndex = 0

We will begin from index 1 and focus on a scenario where two elements are not equal i.e. array[i] !== last. In such cases, we need to add the count of the same element encountered so far like this:

result.push(i - lastSameIndex);

After that, update the value and index to mark the new element that needs to be counted again.

lastSameIndex = i;
last = array[i];

Additionally, handling the case when the loop reaches its end is important. Here, we push the count of the last element that was being counted from the start or lastSameIndex until the end of the array.

result.push(array.length - lastSameIndex);

Second approach

const array = [ "ball", "batter", "batter", "amount", "amount", "github", "github", "github", "account", "account", "account", "account", "account", "account", "account", "github", "github", "github"];

let lastStr = "",
  num = 0;
const result = array
  .map((s) => {
    if (lastStr !== s) {
      lastStr = s;
      num = num === 0 ? 1 : 0;
    }
    return num;
  })
  .join("")
  .match(/(\d)\1*/g)
  .map((s) => s.length);
  
console.log(result);

Answer 3

Answer №2

As you iterate through each item, check if it is different from the previous one - if so, insert 1; otherwise, increment the last number in the array by 1.

const items = ["ball", "batter", "batter", "amount", "amount", "github", "github", "github", "account", "account", "account", "account", "account", "account", "account", "github", "github", "github"]

const results = [];

items.forEach((item, i) => {
    if (items[i - 1] !== item) return results.push(1);

    const last = results.length - 1;
    results[last] = results[last] + 1;
});

console.log(results);

Answer 4

As you iterate through each item, check if it is different from the previous one - if so, insert 1; otherwise, increment the last number in the array by 1.

const items = ["ball", "batter", "batter", "amount", "amount", "github", "github", "github", "account", "account", "account", "account", "account", "account", "account", "github", "github", "github"]

const results = [];

items.forEach((item, i) => {
    if (items[i - 1] !== item) return results.push(1);

    const last = results.length - 1;
    results[last] = results[last] + 1;
});

console.log(results);

Answer 5

Answer №3

Combine the elements of an array into a string separated by commas using the method array.join(","):
```
ball,batter,batter,amount,amount,github,github,github
```
Utilize regular expressions (regex) with pattern /([a-z]+,)\1*/gi to identify repeated words and get:
```
['ball,', 'batter,batter,', 'amount,amount,', 'github,github,github,...]
```
Determine the number of words in each string of the array by applying s.split(',').length-1

JavaScript Code:

array.join(",").match(/([a-z]+,)\1*/gi).map((s) => `${s.split(',').length-1}`);

Outcome: ['1', '2', '2', '3', '7', '2']

Answer 6

Combine the elements of an array into a string separated by commas using the method array.join(","):
```
ball,batter,batter,amount,amount,github,github,github
```
Utilize regular expressions (regex) with pattern /([a-z]+,)\1*/gi to identify repeated words and get:
```
['ball,', 'batter,batter,', 'amount,amount,', 'github,github,github,...]
```
Determine the number of words in each string of the array by applying s.split(',').length-1

JavaScript Code:

array.join(",").match(/([a-z]+,)\1*/gi).map((s) => `${s.split(',').length-1}`);

Outcome: ['1', '2', '2', '3', '7', '2']

I am interested in tallying up the number of adjacent matching elements within an array and then providing the final count

Answer №1

Answer №2

Answer №3

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