My array includes commas, which is interfering with array.push()

Question

I'm going through freeCodeCamp and am having trouble with their "Return Largest Numbers in Arrays" problem. The issue seems to be with my code for finding every fourth element in the second "for" loop. It looks like it's including the commas from the array "decArray". Any ideas on how to fix this or reorient my thinking process? I appreciate it!

The Instructions:

Return an array consisting of the largest number from each provided sub-array. For simplicity, the provided array will contain exactly 4 sub-arrays.
Remember, you can iterate through an array with a simple for loop, and access each member with array syntax arr[i].
largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]) should return an array.
largestOfFour([[13, 27, 18, 26], [4, 5, 1, 3], [32, 35, 37, 39], [1000, 1001, 857, 1]]) should return [27,5,39,1001].
largestOfFour([[4, 9, 1, 3], [13, 35, 18, 26], [32, 35, 97, 39], [1000000, 1001, 857, 1]]) should return [9, 35, 97, 1000000].

Here's My Code:

function largestOfFour(arr) {
  var decArray = [];    // initialize variable to sort each subarray in descending order
  var finalArray = [];  // initialize variable for final array
  
  // sort array values in descending numerical order instead of by alphabetical order
  function sortNumber(a,b) {
    return a - b;
  }
  
  // loop through initial array to sort each subarray in descending order
  for (var i = 0; i < arr.length; i++) {
    decArray += arr[i].sort(sortNumber).reverse() + ",";
  }
  
  // loop through decArray to find every fourth element
  for (var j = 0; j < decArray.length; j += 4) {
    finalArray.push(decArray[j]);
  }
  
  // return the final array
  return finalArray;
}

// test array
largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);

function largestOfFour (arr) { return arr.map(a => Math.max(...a)); } — Patrick Roberts
– Patrick Roberts, Commented Mar 15, 2018 at 20:14

null · Accepted Answer · 2018-03-15 20:17:28Z

3

decArray is an array so you are supposed to push items there instead of append string to it.

replace below line

decArray += arr[i].sort(sortNumber).reverse() + ",";

with this

decArray.push(...arr[i].sort(sortNumber).reverse());

Let me know if this works for you.

edited Mar 15, 2018 at 20:17

answered Mar 15, 2018 at 20:16

null

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3 Comments

Patrick Roberts Over a year ago

Actually, decArray.push(...arr[i].sort(sortNumber).reverse()); otherwise decArray won't be flat. Good explanation. This is the correct answer.

Luke Orth Over a year ago

@null Your answer worked! Thanks for the help; I didn't even think about the fact that I was appending a string by adding that comma. That makes sense though. I appreciate it!

null Over a year ago

@LukeOrth I am glad this helped.

yajiv · Accepted Answer · 2018-03-15 20:32:55Z

1

Actually the problem with your code is that when you are doing this decArray += arr[i].sort(sortNumber).reverse() + ","; you are converting array to string and at the end decArray will become string with info 5,4,3,1,...., so when you doing decArrayj it will return 3 as it is the fifth element in string, so you getting wrong answer. To solve this either do this finalArray.push(arr[i].sort(sortNumber).reverse()[0]) and remove thrid for loop. or try below code

function largestOfFour(arr){
  var finalArray = [];
	for(i = 0, i2 = arr.length; i<i2; i++) {
      finalArray.push(Math.max.apply(null, arr[i]));
  }
  return finalArray;
}

console.log(largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]));

edited Mar 15, 2018 at 20:32

answered Mar 15, 2018 at 20:21

yajiv

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1 Comment

Patrick Roberts Over a year ago

I didn't downvote this, but I will point out while this is correct information, this does not answer the question about the originally attempted implementation.

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