Fill up array with missing data points with ES6

Question

I have got a data sample:

{
  data: [
    { day: 0, amount: 0 },
    { day: 3, amount: 5 },
    { day: 7, amount: 8 },
    { day: 8, amount: 14 }
  ]
}

For doing some math and calculating local regressions I need to fill up each missing day, while I know the total amount of days.

Lets say there are 10 days with the example above, this should be my outcome:

{
  data: [
    { day: 0, amount: 0 },
    { day: 1, amount: 0 },
    { day: 2, amount: 0 },
    { day: 3, amount: 5 },
    { day: 4, amount: 5 },
    { day: 5, amount: 5 },
    { day: 6, amount: 5 },
    { day: 7, amount: 8 },
    { day: 8, amount: 14 }
    { day: 9, amount: 14 }
  ]
}

How can I achieve this in style? (optional with ES6 syntax)

My own guess seems to be quite complicated:

First I could create an array with each day:

const amountOfTotalDays = 10;
const daysByAmount = [
  { day: 0, amount: 0 },
  { day: 3, amount: 5 },
  { day: 7, amount: 8 },
  { day: 8, amount: 14 }
];
const daysHelper = [...Array(amountOfTotalDays).keys()];

Then I could loop over each entry and check for the correct amount. Maybe like this:


    const daysByAmountUpfilled = [];
    daysHelper.map(d => {
      const existingDay = daysByAmount.findIndex(entry => entry.day === d);
      if(existingDay >= 0) {
        daysByAmountUpfilled.push(
          daysByAmount[existingDay]
        );
      } else {
        // find previous entry closest to this day
        // but I do not know how
      }
    });

You could consider trying a for loop and matching on the array index. — CoderLee
– CoderLee, Commented Nov 19, 2019 at 16:13

Nina Scholz · Accepted Answer · 2019-11-19 16:16:01Z

4

You could mutate the array and insert the missing parts.

function fill(array, size) {
    var i;
    for (i = 0; i < size; i++) {
        if (array[i] && array[i].day === i) continue;
        array.splice(i, 0, Object.assign({}, array[i - 1], { day: i }));
    }
}

var data = { data: [{ day: 0, amount: 0 }, { day: 3, amount: 5 }, { day: 7, amount: 8 }, { day: 8, amount: 14 } ]};

fill(data.data, 10);
console.log(data);

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

answered Nov 19, 2019 at 16:16

Nina Scholz

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Comments

Tyler Roper · Accepted Answer · 2019-11-19 16:28:34Z

1

One option is to create a new array of your desired length, and use .map() to fill it.

const days = 10;
const data = { data: [ { day: 0, amount: 0 }, { day: 3, amount: 5 }, { day: 7, amount: 8 }, { day: 8, amount: 14 } ] };

const result = (() => {
  let previousAmount = 0;
  return Array.from(Array(days)).map((item,idx) => {
    const existingDay = data.data.find(day => day.day === idx);
    previousAmount = (existingDay || {amount:previousAmount}).amount;
    return existingDay || { day: idx, amount: previousAmount }; 
})})();

console.log(result);

edited Nov 19, 2019 at 16:28

answered Nov 19, 2019 at 16:17

Tyler Roper

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Comments

marc_s · Accepted Answer · 2021-08-24 20:03:44Z

1

You can create a new array and fill in the missing days when appropriate:

const expectedDays = 10;
const result = {
  data: [
    { day: 0, amount: 0 },
    { day: 3, amount: 5 },
    { day: 7, amount: 8 },
    { day: 8, amount: 14 }
  ]
};
const fixedResult = {};

fixedResult.data = result.data.reduce((acc, v, i) => {
  const next = result.data[i + 1];
  const missing = next ? next.day : expectedDays;
  const fill = [];
  
  for (let i = v.day; i < missing; i++) {
    fill.push({ day: i, amount: v.amount });
  }
  
  return [...acc, ...fill];
}, []);


console.log(fixedResult);

edited Aug 24, 2021 at 20:03

marc_s

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answered Nov 19, 2019 at 16:16

Tom Faltesek

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