Transforming javascript object list

Question

I need to transform this data:

var data = [
 {a : "fin", year: 1996, value: 1},
 {a : "fin", year: 1997, value: 2},
 {a : "fin", year: 1998, value: 3},
 {a : "fin", year: 1999, value: 4},
 {a : "swe", year: 1996, value: 5},
 {a : "swe", year: 1997, value: 6},
 {a : "swe", year: 1998, value: 7},
 {a : "swe", year: 1999, value: 8}
]

into this:

var data = [
 {a : "fin", years: [1996,1997,1998,1999], values: [1,2,3,4]},
 {a : "swe", years: [1996,1997,1998,1999], values: [5,6,7,8]}
]

Thank you for your help!

Benni Russell · Accepted Answer · 2018-11-18 15:05:40Z

2

Using .filter() method we first check to see if the country in question already has an object in the 'result' array, if it doesn't we push an object formatted, if it already exists we find the object using .find() method and push the year and value to the years and values arrays within the object.

let result = [];

data.forEach(element => {
    if (result.filter(obj => obj.a === element.a).length < 1) {
        result.push({a : element.a, years: [element.year], values: [element.value]})
    } else {
        result.find(country => country.a === element.a).years.push(element.year)
        result.find(country => country.a === element.a).values.push(element.value)
    }
})

console.log(result);

edited Nov 18, 2018 at 15:05

answered Nov 18, 2018 at 14:13

Benni Russell

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2 Comments

vinkki Over a year ago

I have multiple countries in the real problem.

Benni Russell Over a year ago

@vinkki I have updated the solution to work with any number of countries dynamically adding the objects to the result array.

fmontes · Accepted Answer · 2018-11-18 14:28:33Z

Is not that pretty but you'll get the idea:

var data = [
 {a : "fin", year: 1996, value: 1},
 {a : "fin", year: 1997, value: 2},
 {a : "fin", year: 1998, value: 3},
 {a : "fin", year: 1999, value: 4},
 {a : "swe", year: 1996, value: 5},
 {a : "swe", year: 1997, value: 6},
 {a : "swe", year: 1998, value: 7},
 {a : "swe", year: 1999, value: 8}
]

var results = [];
data.forEach((item, i) => {
  let exitingIndex = getPosition(item.a);

  if (exitingIndex !== undefined) {
    results[exitingIndex].year.push(item.year)
    results[exitingIndex].value.push(item.value)
  } else {
    results.push({
      a: item.a,
      year: [item.year],
      value: [item.value]
    });
  }
})

function getPosition(value) {
  let res;
  results.forEach((item, index) => {
      if (item.a === value) {
        res = index;
        return;
      }
  })

  return res;
}

console.log(results);

This works, thanks a lot for your help. If you find a better solution let me know. :)
With lodash it should be one line, but I don’t know if in your case it worth to add a library just for that.

Bala · Accepted Answer · 2018-11-18 14:51:21Z

Check whether this works.

    let data = [
    { a: "fin", year: 1996, value: 1 },
    { a: "fin", year: 1997, value: 2 },
    { a: "fin", year: 1998, value: 3 },
    { a: "fin", year: 1999, value: 4 },
    { a: "swe", year: 1996, value: 5 },
    { a: "swe", year: 1997, value: 6 },
    { a: "swe", year: 1998, value: 7 },
    { a: "swe", year: 1999, value: 8 }
]
let groupByCountries = {};
data.forEach(country => {
    if (!groupByCountries.hasOwnProperty(country.a)) {
        groupByCountries[country.a] = {
            years: [country.year],
            values: [country.value]
        }
    }
    else {
        groupByCountries[country.a].years.push(country.year);
        groupByCountries[country.a].values.push(country.value);
    }
})

let combinedValues = []
Object.keys(groupByCountries).forEach(country => {
    combinedValues.push({
        a: country,
        years: groupByCountries[country].years,
        values: groupByCountries[country].values
    })
})

//just for printing
combinedValues.forEach((country) => {
    console.log(country)
})



let data = [
    { a: "fin", year: 1996, value: 1 },
    { a: "fin", year: 1997, value: 2 },
    { a: "fin", year: 1998, value: 3 },
    { a: "fin", year: 1999, value: 4 },
    { a: "swe", year: 1996, value: 5 },
    { a: "swe", year: 1997, value: 6 },
    { a: "swe", year: 1998, value: 7 },
    { a: "swe", year: 1999, value: 8 }
]
let groupByCountries = {};
data.forEach(country => {
    if (!groupByCountries.hasOwnProperty(country.a)) {
        groupByCountries[country.a] = {
            years: [country.year],
            values: [country.value]
        }
    }
    else {
        groupByCountries[country.a].years.push(country.year);
        groupByCountries[country.a].values.push(country.value);
    }
})

let combinedValues = []
Object.keys(groupByCountries).forEach(country => {
    combinedValues.push({
        a: country,
        years: groupByCountries[country].years,
        values: groupByCountries[country].values
    })
})

//just for printing
combinedValues.forEach((country) => {
    console.log(country)
})

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