3-stocks.js

/*
    THESE EXERCISES ARE QUITE HARD. JUST DO YOUR BEST, AND COME WITH QUESTIONS IF YOU GET STUCK :)

    Imagine we a working for a finance company. Below we have:
        - an array of stock tickers
        - an array of arrays containing the closing price for each stock in each of the last 5 days.
            For example, CLOSING_PRICES_LAST_5_DAYS_FOR_ALL_STOCKS[2] contains the prices for the last 5 days for STOCKS[2] (which is amzn)
*/

/* ======= Stock data - DO NOT MODIFY ===== */
const STOCKS = ["aapl", "msft", "amzn", "googl", "tsla"];

const CLOSING_PRICES_LAST_5_DAYS_FOR_ALL_STOCKS = [
    [179.19, 180.33, 176.28, 175.64, 172.99], // AAPL
    [340.69, 342.45, 334.69, 333.20, 327.29], // MSFT
    [3384.44, 3393.39, 3421.37, 3420.74, 3408.34], // AMZN
    [2951.88, 2958.13, 2938.33, 2928.30, 2869.45], // GOOGL
    [1101.30, 1093.94, 1067.00, 1008.87, 938.53] // TSLA
];

/*
    We want to understand what the average price over the last 5 days for each stock is.
    Implement the below function, which
        - Takes this CLOSING_PRICES_LAST_5_DAYS_FOR_ALL_STOCKS array as input (remember, it's an array of arrays)
        - Returns an array containing the average price over the last 5 days for each stock. 
            For example, the first element of the resulting array should contain Apple’s (aapl) average stock price for the last 5 days.
            The second element should be Microsoft's (msft) average price, and so on.
    The average value should be rounded to 2 decimal places, and should be a number (not a string)

    Hint 1: To calculate the average of a set of values, you can add them together and divide by the number of values.
        So the average of 5, 10 and 20 is (5 + 10 + 20) / 3 = 11.67
    Hint 2: If the problem seems complex, try breaking it down into smaller problems.
        Solve the smaller problems, and then build those solutions back up to solve the larger problem.
        Functions can help with this!
*/

/*
    SOLUTION EXPLANATION: This is quite a complex problem and there are several ways to solve it.
          I decided to divide the big problem into several smaller ones.
              1. In the exercise we are asked to find the average price of EACH stock.
                  So maybe we can just work out how to get the average price for a single stock.
                  To do this, I created a separate function called getAveragePricesForStock.
              2. We also need to work out how to round a number to 2 decimal places.
                  There is also a separate function for this called roundTo2Decimals.
              3. We can put these smaller solutions together to solve a bigger problem.
                  The top-level price function getAveragePrices can loop through an array,
                  and pass each subarray to the getAveragePricesForStock function.
*/                 
function getAveragePrices(closingPricesForAllStocks) {
   let averages = [];

   for (let pricesForStock of closingPricesForAllStocks) {
        averages.push(getAveragePricesForStock(pricesForStock));
   }

   return averages;
}

function getAveragePricesForStock(pricesForStock) {
    let total = 0;

    for(let price of pricesForStock) {
        total += price;
    }

    return roundTo2Decimals(total / pricesForStock.length);
}

function roundTo2Decimals(num) {
    return Math.round(num * 100) / 100;
}

/*
    We also want to see what the change in price is from the first day to the last day for each stock.
    Implement the below function, which
        - Takes this CLOSING_PRICES_LAST_5_DAYS_FOR_ALL_STOCKS array as input (remember, it's an array of arrays)
        - Returns an array containing the price change over the last 5 days for each stock.
            For example, the first element of the resulting array should contain Apple’s (aapl) price change for the last 5 days.
            In this example it would be:
                (Apple's price on the 5th day) - (Apple's price on the 1st day) = 172.99 - 179.19 = -6.2
    The price change value should be rounded to 2 decimal places, and should be a number (not a string)
*/

/*
    SOLUTION EXPLANATION: Again, as in the previous solution, we can divide a large problem into several smaller ones.
              1. I created a new function that simply calculates the price change of ONE stock - getPriceChangeForStock.
              2. This new function can also use the roundTo2Decimals function we used before.
                  One of the biggest benefits of using this feature is the ability to reuse code!
*/  

function getPriceChanges(closingPricesForAllStocks) {
    let changes = [];
    
    for(let pricesForStock of closingPricesForAllStocks) {
        changes.push(getPriceChangeForStock(pricesForStock))
    }

    return changes;
}

function getPriceChangeForStock(pricesForStock) {
    let priceChange = pricesForStock[pricesForStock.length - 1] - pricesForStock[0]
    return roundTo2Decimals(priceChange);
}

/*
    As part of a financial report, we want to see what the highest price was for each stock in the last 5 days.
    Implement the below function, which
        - Takes 2 parameters:
            - the CLOSING_PRICES_LAST_5_DAYS_FOR_ALL_STOCKS array as input (remember, it's an array of arrays)
            - the STOCKS array
        - Returns an array of strings describing what the highest price was for each stock.
            For example, the first element of the array should be: "The highest price of AAPL in the last 5 days was 180.33"
            The test will check for this exact string.
    The stock ticker should be capitalised.
    The price should be shown with exactly 2 decimal places.
*/

/*
    EXPLANATION : We can also break this problem down into smaller problems.
                1. I created a new function that simply calculates the highest price for a single stock - getHighestPrice.
                2. This new function can also use the roundTo2Decimals function
               Here I have included an alternative solution that uses JavaScript's Math.max() function
                The Math.max() function accepts zero or more numbers as input parameters.
                We can convert our array into individual numbers, which can then be passed to this function using the propagation syntax: ...
*/ 

function highestPriceDescriptions(closingPricesForAllStocks, stocks) {
   let descriptions = [];

   for(let i = 0; i < closingPricesForAllStocks.length; i++) {
       let highestPrice = getHighestPrice(closingPricesForAllStocks[i]);
       descriptions.push(`The highest price of ${stocks[i].toUpperCase()} in the last 5 days was ${highestPrice.toFixed(2)}`);
   }

   return descriptions;

   }

function getHighestPrice(pricesForStock) {
    //initialising to 0, as we are expecting this value to be overriden by the first price in the array
    let highestPriceSoFar = 0;

    for(let price of pricesForStock) {
        //if this price is higher than the highestprice we are seen so far, it becomes the new highest price
        if(price > highestPriceSoFar) {
            highestPriceSoFar = price;
        }
    }

    return highestPriceSoFar;
}

function highestPriceDescriptionsAllternate(closingPricesForAllStocks, stocks) {
    let descriptions = [];

    for(let i = 0; i < closingPricesForAllStocks.length; i++) {
        let highestPrice = Math.max(...closingPricesForAllStocks[i]);
        descriptions.push(`The highest price of ${stocks[i].toUpperCase()} in the last 5 days was ${highestPrice.toFixed(2)}`);
    }

    return descriptions;

}



/* ======= TESTS - DO NOT MODIFY ===== */
test("should return the average price for each stock", () => {
    expect(getAveragePrices(CLOSING_PRICES_LAST_5_DAYS_FOR_ALL_STOCKS)).toEqual(
        [176.89, 335.66, 3405.66, 2929.22, 1041.93]
    );
});

test("should return the price change for each stock", () => {
    expect(getPriceChanges(CLOSING_PRICES_LAST_5_DAYS_FOR_ALL_STOCKS)).toEqual(
        [-6.2, -13.4, 23.9, -82.43, -162.77]
    );
});

test("should return a description of the highest price for each stock", () => {
    expect(highestPriceDescriptions(CLOSING_PRICES_LAST_5_DAYS_FOR_ALL_STOCKS, STOCKS)).toEqual(
        [
            "The highest price of AAPL in the last 5 days was 180.33",
            "The highest price of MSFT in the last 5 days was 342.45",
            "The highest price of AMZN in the last 5 days was 3421.37",
            "The highest price of GOOGL in the last 5 days was 2958.13",
            "The highest price of TSLA in the last 5 days was 1101.30"
        ]
    );
});