JavaScript: Calculating average spending for customers from an array of purchase records

Other Questions JavaScript
1

I require assistance in determining the average spending for each customer based on an array of purchase records. Below is my data structure:

const purchases = [
  { customer: "Emma", amount: 180 },
  { customer: "Jake", amount: 320 },
  { customer: "Emma", amount: 220 },
  { customer: "Mike", amount: 450 },
  { customer: "Jake", amount: 160 },
  { customer: "Sarah", amount: 90 },
  { customer: "Mike", amount: 250 }
];

I created the following function, but I’m facing issues with it:

function calculateAverageSpending(data) {
  const totals = {};
  data.forEach(transaction => {
    const customer = transaction.customer;
    totals[customer] = (totals[customer] || 0) + transaction.amount;
  });

  const averages = {};
  for (const amount in totals) {
    if (totals.hasOwnProperty(amount) && typeof amount === 'number') {
      averages[amount] = totals[amount] / 2; // Incorrect divisor being used
    }
  }

  return averages;
}

console.log(calculateAverageSpending(purchases));

Currently, this code only returns the total spending for each customer, but I am unsure how to divide this by the correct number of purchases. My goal is to create an output like this:

{
  Emma: 200,
  Jake: 240,
  Mike: 350,
  Sarah: 90
}

How can I effectively track both the total spending and the number of purchases for each customer to calculate the accurate average?

2

quick fix - you don’t need two separate objects. just store both values in one object like {total: 0, count: 0} then divide at the end. also, that typeof amount === 'number' won’t work since object keys are always strings in js.

3

Your loop’s broken because you’re iterating over amount instead of customer names, and that typeof amount === 'number' check will never work since object keys are always strings. You also need to track how many purchases each customer made. Here’s the fix:

function calculateAverageSpending(data) {
  const totals = {};
  const counts = {};
  
  data.forEach(transaction => {
    const customer = transaction.customer;
    totals[customer] = (totals[customer] || 0) + transaction.amount;
    counts[customer] = (counts[customer] || 0) + 1;
  });

  const averages = {};
  for (const customer in totals) {
    averages[customer] = totals[customer] / counts[customer];
  }

  return averages;
}

I added a separate counts object to track purchases per customer and fixed the iteration to loop over customer names instead of amounts. That’ll get you the right averages.

4

Your second loop’s the problem - you’re iterating over amount instead of customer names. Plus hardcoding the divisor as 2 won’t work when customers have different purchase counts. I’ve hit similar data aggregation issues before and reduce() makes this way cleaner:

function calculateAverageSpending(data) {
  const customerStats = data.reduce((acc, transaction) => {
    const customer = transaction.customer;
    if (!acc[customer]) {
      acc[customer] = { total: 0, count: 0 };
    }
    acc[customer].total += transaction.amount;
    acc[customer].count += 1;
    return acc;
  }, {});

  const averages = {};
  for (const customer in customerStats) {
    averages[customer] = customerStats[customer].total / customerStats[customer].count;
  }
  return averages;
}

This does the data collection in one pass and fixes the variable naming mess from your original code.