Aggregate and average values inside an object Javascript-CodePudding

I have an object in the form of:

{
"Dates": ["January", "January", "March", "March", "March", "November", "November"],
"Values": [45.6, 0.5, 59.3, 46.56, 2.21, 48.59, 5.5]
}

What I need is to aggregate the values in "Values" (average) by month

The object I am seeking:

{
"Dates":["January", "March", "November"],
"Values":[23.05, 36.02, 27]
}

I know there have been several posts about it here. But I am not sure how to apply it to an object with arrays. Would appreciate very much any ideas. Thanks

CodePudding user response：

Something like this should work.

// First reduce the data to an object with the dates as keys
const grouped = data.Dates.reduce((acc, date, i) => {
  if (acc[date]) {
    acc[date].push(data.Values[i])
  } else {
    acc[date] = [data.Values[i]]
  }
  return acc
}, {});

// Then reduce the object to the desired format
const result = Object.keys(grouped).reduce((acc, date) => {
  acc.Dates.push(date)
  acc.Values.push(grouped[date].reduce((a, b) => a   b) / grouped[date].length)
  return acc
}, {Dates: [], Values: []});

CodePudding user response：

You could try something like this.

const obj = {
  "Dates": ["January", "January", "March", "March", "March", "November", "November"],
  "Values": [45.6, 0.5, 59.3, 46.56, 2.21, 48.59, 5.5]
}

// new Set() will remove all duplicated items
const months = [...new Set(obj.Dates)];

const result = {
  "Dates": months,
  "Values": months.map(month => {
    // find values for given month
    const values = obj.Values.filter((_, i) => obj.Dates[i] === month);
    
    // sum the values and divide by the amount
    return values.reduce((a, b) => a   b) / values.length;
  })
}

console.log(result);

CodePudding user response：

You could split the tasks into smaller parts and use functions for

grouping,
getting an average of an array
getting the complete result by taking an object of groups.

const
    getAverage = array => array.reduce((a, b) => a   b) / array.length,
    groupBy = (keys, values) => {
        const groups = {};

        for (let i = 0; i < keys.length; i  )
            (groups[keys[i]] ??= []).push(values[i]);

        return groups;
    },
    getAverages = groups => Object.entries(groups).reduce((r, [month, values]) => {
        r.Dates.push(month);
        r.Values.push(getAverage(values));
        return r;
    }, { Dates: [], Values: [] }),
    data = { Dates: ["January", "January", "March", "March", "March", "November", "November"], Values: [45.6, 0.5, 59.3, 46.56, 2.21, 48.59, 5.5] },
    result = getAverages(groupBy(data.Dates, data.Values));

console.log(result);

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