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expand a string in JavaScript to display letter and how many times that letter appears

Write a function that accepts a string where letters are grouped together and returns new string with each letter followed by a count of the number of times it appears.
example : ('aeebbccd') should produce // 'a1e2b2c2d1'
function strExpand(str) {
let results = ""
for (let i = 0; i < str.length; i++) {
let charAt = str.charAt(i)
let count = 0
results += charAt
for (let j = 0; j < str.length; j++) {
if (str.charAt(j) === charAt) {
count++;
}
}
results += count;
}
return results;
}
with the input 'aeebbccd' I am getting 'a1e2e2b2b2c2c2d1' instead of 'a1e2b2c2d1'

This function is adding a number after each character, which is the number of times this character appears anywhere in the string. You could instead do it like this to get the result you want.
function strExpand(str) {
let output = "";
// Iterate through each character of the string, appending
// to the output string each time
for (let i = 0; i < str.length; i++) {
let count = 1;
// If the next character is the same, increase the count
// and increment the index in the string
while (str[i + 1] == str[i]) {
count++;
i++;
}
// Add the character and the count to the output string
output += str[i] + count;
}
return output;
}

For sake of completeness,
how about a Regex?
const pattern = /(.)\1*/g; // put a char that exists in a capture group, then see if it repeats directly after
const s = 'aeebbccd';
var result = '';
for (match of s.match(pattern)) {
let this_group = match;
let this_len = match.length;
result = result + this_group[0] + this_len; // get only the first letter from the group
}
console.log(result); // a1e2b2c2d1

This would to the job. edit: hah i see im late :D, but still nice functional way to solve that.
/**
* #param string to count
* #return string $characterA$count. ex. abbccc -> a1b2c3
*/
function toCharacterCountString(str) {
return Array.from(new Set(str).values())
.map(char => {
return `${char}${(str.match(new RegExp(char, "g")) || []).length}`;
}).join('');
}
console.log(toCharacterCountString('abbccc')); // a1b2c3
console.log(toCharacterCountString('aeebbccd')); // a1e2b2c2d1

Javascript for loop not iterating across array or values in an if statement not updating as planned

Trying to return the highest 5 digit number out of any given number i.e 34858299999234
will return 99999
I think I have it narrowed down to the for loop not iterating the array properly OR the values for 'hold1' and 'hold2' are not updating.
function solution(digits){
//Convert string to array to iterate through
let arr = digits.split("");
let final = 0;
//iterate through the array in 5 sequence steps
for(let i = 0; i < arr.length-1; i++){
let hold1 = arr[i] + arr[i+1] + arr[i+2] + arr[i+3] + arr[i+4];
hold1 = parseInt(hold1,10); //converting string to int so if statement functions correctly
let hold2 = arr[i+1] + arr[i+2]+ arr[i+3] + arr[i+4] + arr[i+5];
hold2 = parseInt(hold2,10);
if(hold1 >= hold2){
final = hold1;
}else{
final = hold2;
}
return final;
}
}

if you need a five digits result you need to change the for loop in something like this:
for (let i = 0; i < arr.length - 5; i++) {
Otherwise you will generate results shorter than 5 digits.
Also, I think you are missing the Math.max method that will compare two numbers to return the bigger one.
I rewrote your function this way:
function solution(digits) {
let op = 0;
let length = 5;
let stringDigits = String(digits); /// <-- I use string instead of array
if (stringDigits.length <= length) {
return digits; /// <-- If input is shorter than 5 digits
}
for (let i = 0; i < stringDigits.length - length; i++) {
const fiveDigitsValue = stringDigits.substr(i, length);
op = Math.max(op, Number(fiveDigitsValue));
}
return op;
}

Finding the sum of a "counter" variable loop that ran ten times then was pushed into the "numbers" array. Each way I tried resulted with a list

I'm asking for help to find the sum of an array with elements that were pushed from a counter variable that had previously looped 10 times. I'm new to Javascript and was practicing for an assessment, and I've tried several different ways to do it and have only resulted with just a list of the elements within the numbers array.
var counter = 10;
var numbers = [];
for (i = 1; i <= 10; i ++) {
counter = [i + 73];
numbers.push(counter);
}
console.log(numbers);
function sum(arr) {
var s = 0;
for(var i = 0; i < arr.length; i++) {
s = s += arr[i];
}
return s;
}
console.log(sum([numbers]));
function getArraySum(a) {
var total = 0;
for (var i in a) {
total += a[i];
}
return total;
}
var numbers = getArraySum([numbers]);
console.log(numbers);

you should push only the value of counter without the brackets and then make a reduce to have the sum of each number in the array
var counter = 10;
var numbers = [];
for (i = 1; i <= 10; i++) {
counter = i + 73;
numbers.push(counter);
}
console.log(numbers.reduce((a,b) => a+b));

You had a couple of typos in the code:
Typos
You were wrapping the sum in square brackets:
counter = [i + 73];
You should just remove the brackets like:
counter = i + 73;
2. You were wrapping a value that is already an array in square brackets while passing it as an argument to a function:
sum( [numbers] )
// ...
getArraySum( [numbers] );
You should remove the brackets, like this:
sum( numbers );
// ...
getArraySum( numbers );
Fix
I updated the code that you shared to fix the above-mentioned things:
var numbers = [];
// Loop 10 times and push each number to the numbers array
for (var i = 1; i <= 10; i ++) {
var sumNumbers = i + 73;
numbers.push(sumNumbers);
}
console.log(numbers);
function sum(arr) {
var total = 0;
for(var i = 0; i < arr.length; i++) {
total += arr[i];
}
return total;
}
// Call the function by passing it the variable numbers, holding an array
var result1 = sum(numbers);
console.log( result1 );
function getArraySum(a) {
var total = 0;
for (var i in a) {
total += a[i];
}
return total;
}
var result2 = getArraySum(numbers);
console.log(result2);

want to get a count of repeated values on an array [duplicate]

This question already has answers here:
JavaScript function to automatically count consecutive letters in a string
(5 answers)
Closed 1 year ago.
I am a beginner in javascript, I want to get a count of repeated values on an array
I have a string "aaaaaabbbbbbbcccccccaa" and I want the output array be like ["a6", "b7", "c7", "a2"];
I tied but failed. Please help me out
Thanks In Advance :)
var a = "aaaaaabbbbbbbcccccccaa";
function aa(data){
var a = [];
var x = [];
//var b = data.split("")
// var b = data.split("").filter((val,key, arr)=>{
// //console.log(arr.indexOf(val) +" "+ key )
// return arr.indexOf(val) === key
// })
//console.log(b);
for(let i = 0; i<= data.length-1; i++){
for(let j = 0; j<= data.length-1; j++){
if(data[i] !== data[j] && x.indexOf(data[i]+""+j) <0){
x.push(data[i]+""+j);
a.push(data[i] +""+ j);
break;
}
}
}
console.log(x);
return a;
}
console.log(aa(a));

I'd use a regular expression to match repeated characters in the string, then map them to match[0] + match.length to get the concatenated substring for that portion:
const aa = data => data
.match(/(.)\1*/g)
.map(match => match[0] + match.length);
console.log(aa('aaaaaabbbbbbbcccccccaa'));
If you don't want to use a regular expression, don't use a nested loop like that from 0 to the string length - instead, count up repeated characters from inside the first loop, starting at the current i index and incrementing it:
function aa(data) {
const result = [];
for (let i = 0; i < data.length; i++) {
const char = data[i];
let matches = 1;
while (data[i + 1] === char) {
i++;
matches++;
}
result.push(char + matches);
}
return result;
}
console.log(aa('aaaaaabbbbbbbcccccccaa'));

Iterating through a number and rearranging in descending

I'm trying to rearrange an input number using a function so that a single number is rearranged into descending order.
For example, 234892 would result in 984322.
This is what I have come up with.
function descendingOrder(n){
var num = '';
for(var i = 0; i <= n.length + 1; i++){ // iterates through the number
for(var j = 9; j >= 0; j--){ // starts at 9 and checks numbers descending
if (j == n[i]){
num.push(n[i]); // checks if j == n[i] and if so, pushes to num
}
i = 0; // sets i back to 0 to rescan the number again
}
}
return num;
}

You can convert number to string, split each character, sort it and join it again:
+(234892 + '').split('').sort((a, b) => a < b).join('');
var ordered = +(234892 + '').split('').sort((a, b) => a < b).join('');
document.getElementById('output').appendChild(document.createTextNode(ordered));
234892 → <span id="output"></span>
Detailed explanation:
var str = 234892 + ''; // convert to string
var parts = str.split(''); // convert to array of characters
// sort
parts.sort(function(a, b) {
return a < b;
});
var finalStr = parts.join(''); // join characters to string
var finalNumber = +finalStr; // convert back to number
console.log(finalNumber); // 984322