Locate the closest array index to ensure precise calculations

Question

Locate the closest array index to ensure precise calculations

While working on a Javascript project, I encountered an issue where I needed to calculate the "Price/Earnings Ratio" from a finance API. However, the API did not have a direct method to retrieve the required value.

The formula for computing the Price/Earnings Ratio for a specific year is as follows:

Last Stock Price of Mentioned Date / Date Earnings Per Share

The problem arose when I had the following data:

let as-of-date = "2019-12-31";
    let as-of-date-eps = 2.00;
    let ratio-as-of-date = as-of-date-eps/?

Unfortunately, the array containing the nearest stock prices for the mentioned date did not include the specific date "2019-12-31". To accurately compute the Price/Earnings Ratio, I needed to find the index of the nearest stock price entry before that date. In this case, it was the second index or stock-price-history[1].last, resulting in an expected Price/Earnings Ratio of 4.095.

My question now is how can I write the code to ensure that I obtain the correct result?

javascript arrays

Answer 1

Answer №1

Simplifying things:

Find the difference between each item's date and the chosen date
Store these indexes and differences in an array
Sort this array by the differences
Select the first index from the sorted array as the minIndex
Use this minIndex to retrieve the relevant item from your stockPriceHistory array

Please note: the minimum offset can be calculated as "2020-01-02" - "2019-12-31" = 2 days, whereas "2020-12-27" - "2019-12-31" = -4 days. Is the logic to exclude any dates that are ahead of the chosen date?

const chosenDate = new Date("2019-12-31");
const stockPriceHistory = [
        {
            "date": "2019-12-26",
            "open": 8.3,
            "high": 8.48,
            "low": 8.2,
            "last": 8.21,
            "volume": 162800
        },
        {
            "date": "2019-12-27",
            "open": 8.48,
            "high": 8.48,
            "low": 8,
            "last": 8.19,
            "volume": 113000
        },
        {
            "date": "2020-01-02",
            "open": 8.45,
            "high": 8.48,
            "low": 8.2,
            "last": 8.4,
            "volume": 100000
        },
];

const dateOffsetsByIndex = stockPriceHistory.map((item, index) => {
  const currDate = new Date(item.date);
  const offset = (currDate - chosenDate) / (1000 * 60 * 60 * 24); //days
  return [index, offset];
})
  .sort((a,b) => {
    if (a[1] > 0 && b[1] < 0){
      return 1;
    }
    if (a[1] < 0 && b[1] > 0){
      return -1;
    }
    return Math.abs(a[1]) - Math.abs(b[1])
  });

const minIndex = dateOffsetsByIndex[0][0];

console.log(stockPriceHistory[minIndex]);

A cleaner version using reduce could be:

const chosenDate = new Date("2019-12-31");
const stockPriceHistory = [
        {
            "date": "2019-12-26",
            "open": 8.3,
            "high": 8.48,
            "low": 8.2,
            "last": 8.21,
            "volume": 162800
        },
        {
            "date": "2019-12-27",
            "open": 8.48,
            "high": 8.48,
            "low": 8,
            "last": 8.19,
            "volume": 113000
        },
        {
            "date": "2020-01-02",
            "open": 8.45,
            "high": 8.48,
            "low": 8.2,
            "last": 8.4,
            "volume": 100000
        },
];

const minOffset = stockPriceHistory.reduce((agg, item) => {
  const currDate = new Date(item.date);
  const offset = (currDate - chosenDate) / (1000 * 60 * 60 * 24); //days
  if (!agg.offset) return  {...item, offset};
  if (agg.offset > 0 && offset < agg.offset) return {...item, offset}; 
  if (agg.offset < 0 && (offset > agg.offset && offset <=0)) return {...item, offset};
  return agg;
}, {});

console.log(minOffset);

Answer 2

Simplifying things:

Find the difference between each item's date and the chosen date
Store these indexes and differences in an array
Sort this array by the differences
Select the first index from the sorted array as the minIndex
Use this minIndex to retrieve the relevant item from your stockPriceHistory array

Please note: the minimum offset can be calculated as "2020-01-02" - "2019-12-31" = 2 days, whereas "2020-12-27" - "2019-12-31" = -4 days. Is the logic to exclude any dates that are ahead of the chosen date?

const chosenDate = new Date("2019-12-31");
const stockPriceHistory = [
        {
            "date": "2019-12-26",
            "open": 8.3,
            "high": 8.48,
            "low": 8.2,
            "last": 8.21,
            "volume": 162800
        },
        {
            "date": "2019-12-27",
            "open": 8.48,
            "high": 8.48,
            "low": 8,
            "last": 8.19,
            "volume": 113000
        },
        {
            "date": "2020-01-02",
            "open": 8.45,
            "high": 8.48,
            "low": 8.2,
            "last": 8.4,
            "volume": 100000
        },
];

const dateOffsetsByIndex = stockPriceHistory.map((item, index) => {
  const currDate = new Date(item.date);
  const offset = (currDate - chosenDate) / (1000 * 60 * 60 * 24); //days
  return [index, offset];
})
  .sort((a,b) => {
    if (a[1] > 0 && b[1] < 0){
      return 1;
    }
    if (a[1] < 0 && b[1] > 0){
      return -1;
    }
    return Math.abs(a[1]) - Math.abs(b[1])
  });

const minIndex = dateOffsetsByIndex[0][0];

console.log(stockPriceHistory[minIndex]);

A cleaner version using reduce could be:

const chosenDate = new Date("2019-12-31");
const stockPriceHistory = [
        {
            "date": "2019-12-26",
            "open": 8.3,
            "high": 8.48,
            "low": 8.2,
            "last": 8.21,
            "volume": 162800
        },
        {
            "date": "2019-12-27",
            "open": 8.48,
            "high": 8.48,
            "low": 8,
            "last": 8.19,
            "volume": 113000
        },
        {
            "date": "2020-01-02",
            "open": 8.45,
            "high": 8.48,
            "low": 8.2,
            "last": 8.4,
            "volume": 100000
        },
];

const minOffset = stockPriceHistory.reduce((agg, item) => {
  const currDate = new Date(item.date);
  const offset = (currDate - chosenDate) / (1000 * 60 * 60 * 24); //days
  if (!agg.offset) return  {...item, offset};
  if (agg.offset > 0 && offset < agg.offset) return {...item, offset}; 
  if (agg.offset < 0 && (offset > agg.offset && offset <=0)) return {...item, offset};
  return agg;
}, {});

console.log(minOffset);

Locate the closest array index to ensure precise calculations

Answer №1

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