How to simplify an array of objects with dynamic key names and a nested array into a simpler format?

I am trying to transform an array of objecst with keys: name and winRatio to another array of objects with a key of each unique name and value of an item in the winRatio array.

The purpose of this problem is to transform incomming data and reformat it into a chart realizing solution (Recharts, if you’re interested)

Input

const data = [
  {
    name: 'Tyler',
    winRatio: [1, 0.5, 0.6666666666666666],
  },
  {
    name: 'Lizzie',
    winRatio: [0, 0.5, 0.3333333333333333],
  },
];

Output

const formatted = [
  {
    index: 0,
    Tyler: 1,
    Lizzie: 0,
  },
  {
    index: 1,
    Tyler: 0.5,
    Lizzie: 0.5,
  },
 {
    index: 2,
    Tyler: 0.6666,
    Lizzie: .333,
  },
];

I thought about using map and reduce array functions, but I can’t quite seem to wrap my mind around that.

Note Additionally, each object in the output should have an index value associated with the object that increments by one.

Note The length of the outputed array should be equal to the longest length of any winRatio array. For example, if the winRatio for ‘Tyler’ has 20 items, the output array should have 20 objects.

Answer

Here’s one way you could use a reducer to do it. It loops through the data array, taking each players object and combining it into the final array in the format you requested.

const reducer = (previousValue, currentValue,index) => {
    let current = {}

    currentValue.winRatio.forEach( (x, index) => {
        current = previousValue[index] ?? { index };
        current[currentValue.name] = x
        previousValue[index] = current
    })

    return previousValue
}

data.reduce(reducer, [])

As to your two notes, the output is an array so it should know its index, but you could add a line to the forEach block in this example adding an index key/value pair if one doesn’t exist yet as you loop through. For your second note, I’m not sure how to figure that out without just sorting the array (or going through it and noting the longest winRatio length) first, so I guess you could just do that.