Count Value of multi dimensional array in Javascript

Your sortedArr isn't sorted, so the results are erratic. In JavaScript, sort() modifies the array directly, so you only need to add

sortedArr.sort();

and your code works.

var sortedArr = [["Paul",     "1355"],
  ["Jennifer", "1910"],
  ["John",      "835"],
  ["John",      "830"],
  ["Paul",     "1315"],
  ["John",     "1615"],
  ["John",     "1640"],
  ["Paul",     "1405"],
  ["John",      "855"],
  ["John",      "930"],
  ["John",      "915"],
  ["John",      "730"],
  ["John",      "940"],
  ["Jennifer", "1335"],
  ["Jennifer",  "730"],
  ["John",     "1630"],
  ["Jennifer",    "5"]
];

 count = 1;
 var test;

sortedArr.sort();

for (var i = 0; i < sortedArr.length; i = i + count) {
  count = 1;
  test = [];
  test.push(sortedArr[i][1]);
 
  for (var j = i + 1; j < sortedArr.length; j++) {    
    if (sortedArr[i][0] === sortedArr[j][0]) {
      count++; 
      test.push(sortedArr[j][1]);     
      }
  }
  document.write(sortedArr[i][0]  +test +" = " + count + "<br>");
}

Respecting and understanding the way you are trying to solve the problem, your logic is correct except that it needs a sorted list because your implementation skips consecutive entries with similar names with count it has to be sorted for that. So sorting the array before you check the values will give you the proper results:

sortedArr.sort((a, b) => b.toString().localeCompare(a.toString()));

Note I have sorted the array in descending order to match your output. If you just call sortedArr.sort() it should also give the correct results but in reverse output order.

You can first organize the data and then print it to the document.

1. First you can iterate over the array using Array.prototype.reduce and convert it into object where each field will be <perosn_name> : <array_of_values>.

2. Then again iterate to print in the form of <name> = <comma separated values> = <count> of the values (using Object.entries and Array.prototype.forEach)

Try like below

var sortedArr = [
  ["Paul", "1355"],
  ["Jennifer", "1910"],
  ["John", "835"],
  ["John", "830"],
  ["Paul", "1315"],
  ["John", "1615"],
  ["John", "1640"],
  ["Paul", "1405"],
  ["John", "855"],
  ["John", "930"],
  ["John", "915"],
  ["John", "730"],
  ["John", "940"],
  ["Jennifer", "1335"],
  ["Jennifer", "730"],
  ["John", "1630"],
  ["Jennifer", "5"],
];

// convert the data into the form described
const output = sortedArr.reduce((prevValue, [name, value]) => {
  prevValue[name] ? prevValue[name].push(value) : (prevValue[name] = [value]);
  return prevValue;
}, {});

// write to the document
Object.entries(output).forEach(([name, arr]) => {
  document.write(`${name} = ${arr.join(",")} = ${arr.length}<br>`);
})

NOTE: Always try to use the built-in Array prototype functions. Most of the time you can use them and easy to read your code.

Put all of them in a object, and you can get what you want.

const result = sortedArr.reduce((acc, curr) => {
  const [name, number] = curr
  if (acc[name]) {
    acc[name].push(number)
  } else {
    acc[name] = [number]
  }
  return acc
},{})

// you can use result["Paul"] to get the count of Paul
// don't need to add count variable

You can use Map for this use-case

let map = new Map();

sortedArr.forEach((item)=>{
  let [key, value] = item;
  if(!map.has(key)) {
    map.set(key, [])
  }
  map.get(key).push(value)
})


for(let [key, value] of map.entries()) {
  console.log(`${key} ${value} = ${value.length}`);
}

Output is

Paul 1355,1315,1405 = 3
Jennifer 1910,1335,730,5 = 4
John 835,830,1615,1640,855,930,915,730,940,1630 = 10