How to get max value of each index from multi dimentional array - javascript

Question

This is my first time facing multidimensional array.

I have an array of year like this:

yearArr = [
  [2019, 2018, ''],
  [2019, 2018, 2017],
  ['', 2018, 2017]
]

I need to make a fix year array like:

newYearArr = [ 2019, 2018, 2017 ]

The value at index 0 is the highest value at index 0 of any of the arrays, the value at index 1 is the highest at index 1, etc.

This is what I have done:

var highestValue = []

for(var i = 0; i < yearArr[0].length; i++){
           highestValue.splice(i,0,0)
           for(var j = 0; j < yearArr.length; j++){
             if(yearArr[i][j] > highestValue[i]){
               highestValue[i] = yearArr[i][j]
             }
           }
       }

but it always returns

newYearArr = [2019, 2019, 2019]

sorry but i mean highest value of each index i mean like index 0 is 2019, index 1 is 2018, and index 2 is 2017. — yudistira nugraha
– yudistira nugraha, Commented May 12, 2020 at 8:29
Great, thanks for clarifying! BTW, since this is your 1st exposure to "multidimensional" arrays in JavaScript, just a quick note on that: JavaScript doesn't have multidimensional arrays. What it has instead is arrays that can contain arrays (like yours). In a true multidimensional array, the inside dimensions would be consistent, but because JS has arrays of arrays, each of the arrays inside the outer one can be a different size: [ [1, 2, 3], [1], [1, 2, 3, 4, 5, 6] ]. In fact, there could even be non-arrays in there. I mention it because it helps to know this when trying to work with them. — T.J. Crowder
– T.J. Crowder, Commented May 12, 2020 at 8:38

CertainPerformance · Accepted Answer · 2020-05-12 08:12:34Z

1

The array items at an index are either empty or all the same, so you can iterate over them and assign to the combined array at that index of an item at the index doesn't exist yet:

const yearArr = [
  [2019, 2018, ''],
  [2019, 2018, 2017],
  ['', 2018, 2017]
];
const newYearArr = [];
yearArr.forEach((years) => {
  years.forEach((year, i) => {
    if (!newYearArr[i]) {
      newYearArr[i] = year;
    }
  });
});
console.log(newYearArr);

answered May 12, 2020 at 8:12

CertainPerformance

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Nina Scholz · Accepted Answer · 2020-05-12 08:17:05Z

1

You could take -Infinity for not numbers and get the maximum for each index position.

const
    getN = v => typeof v === 'number' ? v : -Infinity,
    yearArr = [[2019, 2018, ''], [2019, 2018, 2017], ['', 2018, 2017]],
    result = yearArr.reduce((r, a) =>
        a.map((v, i) => Math.max(getN(v), getN(r[i]))), []);

console.log(result);

answered May 12, 2020 at 8:17

Nina Scholz

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