How to reduce two array to get a custom object

Question

I've got two object arrays with float value and string for shorthanded category.

const summer = [
  { _id: 'cat1', Datasets: 496, Average: 27.586688911290324 },
  { _id: 'catB', Datasets: 237, Average: 27.6677358649789 },
  { _id: 'cat3', Datasets: 15, Average: 25.567020000000001 },
  { _id: 'catD', Datasets: 51, Average: 24.998184313725492 }
]

const winter = [
  { _id: 'cat1', Datasets: 496, Average: 17.586688911290324 },
  { _id: 'catB', Datasets: 237, Average: 17.6677358649789 },
  { _id: 'cat3', Datasets: 15, Average: 15.567020000000001 },
  { _id: 'catD', Datasets: 51, Average: 14.998184313725492 }
]

The shorthanded category strings should be 'translated' to the correct category label and the float values should be pushed to the season field.

const target = {
  cat1: { label: 'Cars', index: 0 },
  catB: { label: 'Planes', index: 1 },
  cat3: { label: 'People', index: 2 },
  catD: { label: 'Vegetables', index: 3 }
}

So the result for the example data should be:

{
  labels: [
    'Cars',
    'Planes',
    'People',
    'Vegetables'
  ],
  season: {
    summer: [
      27.586688911290324,
      24.998184313725492,
      27.6677358649789,
      25.567020000000001
    ]
    winter: [
      17.586688911290324,
      14.998184313725492,
      17.6677358649789,
      15.567020000000001
    ]
  },
  title: 'Just a title string'
}

My attempt looks like this, but it handles only one data array:

const result = data.reduce((r, { _id, Average }) => {
    r.labels[target[_id].index] = target[_id].label
    r.season.winter[target[_id].index] = Average
    return r
  }, { labels: [], season: { winter: [] }, title: 'Just a title string' })

the expected output is alittle vague, based on your inputs; may you explain it further — Mechanic
– Mechanic, Commented Mar 1, 2020 at 18:46
@Mhmdrz_A Labels field should get the category label which is stored in target. Average values of each array should get to winter/summer and the title is just any string. — user3142695
– user3142695, Commented Mar 1, 2020 at 18:48
Reduce provides an index if you want to use it (developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… ) — tevemadar
– tevemadar, Commented Mar 1, 2020 at 18:48

Nina Scholz · Accepted Answer · 2020-03-01 19:06:36Z

2

You could take an object with winter and summer as short hand properties and iterate the entries from it.

This approach takes the labels first to prevent for every object a new setting.

const
    getLabels = target => Object.values(target).reduce((r, { label, index }) => {
        r[index] = label;
        return r;
    }, []),
    summer = [{ _id: 'cat1', Datasets: 496, Average: 27.586688911290324 }, { _id: 'catB', Datasets: 237, Average: 27.6677358649789 }, { _id: 'cat3', Datasets: 15, Average: 25.567020000000001 }, { _id: 'catD', Datasets: 51, Average:  4.998184313725492 }],
    winter = [{ _id: 'cat1', Datasets: 496, Average: 17.586688911290324 }, { _id: 'catB', Datasets: 237, Average: 17.6677358649789 }, { _id: 'cat3', Datasets: 15, Average: 15.567020000000001 }, { _id: 'catD', Datasets: 51, Average: 14.998184313725492 }],
    target = { cat1: { label: 'Cars', index: 0 }, catB: { label: 'Planes', index: 1 }, cat3: { label: 'People', index: 2 }, catD: { label: 'Vegetables', index: 3 } },
    result = Object
        .entries({ summer, winter })
        .reduce((r, [key, data]) => {
            r.season[key] = [];
            data.forEach(({ _id, Average }) => r.season[key][target[_id].index] = Average);
            return r;
        }, { labels: getLabels(target), season: { }, title: 'Just a title string' });

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Mar 1, 2020 at 19:06

answered Mar 1, 2020 at 18:49

Nina Scholz

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2 Comments

user3142695 Over a year ago

Why is in the last line season: { winter: [] } without summer? I do not understand this part.

Nina Scholz Over a year ago

no need for this. it is set for any key of the object here: r.season[key] = [];

Sushmit Sagar · Accepted Answer · 2020-03-01 19:23:38Z

const summer = [
  { _id: 'cat1', Datasets: 496, Average: 27.586688911290324 },
  { _id: 'catB', Datasets: 237, Average: 27.6677358649789 },
  { _id: 'cat3', Datasets: 15, Average: 25.567020000000001 },
  { _id: 'catD', Datasets: 51, Average: 24.998184313725492 }
]

const winter = [
  { _id: 'cat1', Datasets: 496, Average: 17.586688911290324 },
  { _id: 'catB', Datasets: 237, Average: 17.6677358649789 },
  { _id: 'cat3', Datasets: 15, Average: 15.567020000000001 },
  { _id: 'catD', Datasets: 51, Average: 14.998184313725492 }
]

const target = {
  cat1: { label: 'Cars', index: 0 },
  catB: { label: 'Planes', index: 1 },
  cat3: { label: 'People', index: 2 },
  catD: { label: 'Vegetables', index: 3 }
}



let desiredObj = {
  labels: [],
  season: {
    summer: [],
    winter: []
  },
  title: 'Just a title string'
}


Object.keys(target).forEach(targetKey => {

  const targetLabel = target[targetKey].label
  const targetIndex = target[targetKey].index

  const summerObjFoundByTargetKey = summer.find(obj => obj['_id'] === targetKey)

  const winterObjFoundByTargetKey = winter.find(obj => obj['_id'] === targetKey)

  desiredObj.labels.push(targetLabel)

  if(summerObjFoundByTargetKey) {
    desiredObj.season.summer[targetIndex] = summerObjFoundByTargetKey.Average
  }

  if(winterObjFoundByTargetKey) {
    desiredObj.season.winter[targetIndex] = winterObjFoundByTargetKey.Average
  }

})


console.log('desiredObj', desiredObj)

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