# Aggregate Functions

We are going to see how to calculate the sum, average, min and max for an array of prices.

I am going to show two ways:

1. the procedural (old) way
2. the aggregate functions (new) way

In general in real world projects, you write procedural code only in edge cases when it's necessary.

# Exercise

We are going to use an array of prices for our example. The type of the array is inferred as double because we have numbers with decimal points.

var prices = new[] { 12, 43.5, 32, 9, 3.0 };

# Sum

Let's see how to calculate the sum procedurally:

var sum = 0d; // d for double
for (int i = 0; i < prices.Length; i++)
{
    sum += prices[i];
}
Console.WriteLine(sum);

But the array provides us with the Sum method which we can call directly:

var sum = prices.Sum();
Console.WriteLine(sum);

# Average

Let's write the procedural code to find out the average. To do this, we need to calculate the sum and then divide it by the total number of items in the array.

var sum = 0d;
for (int i = 0; i < prices.Length; i++)
{
    sum += prices[i];
}
var average = sum / prices.Length;
Console.WriteLine(average);

But, again, the array exposes the Average method which comes in handy:

var average = prices.Average();
Console.WriteLine(average);

# Min

Let's see what is the minimum value in the array:

var min = prices[0];
for (int i = 1; i < prices.Length; i++)
{
    if (prices[i] < min)
    {
        min = prices[i];
    }
}
Console.WriteLine(min);

But again, C# provides us with a Min method for arrays:

var min = prices.Min();
Console.WriteLine(min);

# Max

Let's see what is the maximum value in the array:

var max = prices[0];
for (int i = 1; i < prices.Length; i++)
{
    if (prices[i] > max)
    {
        max = prices[i];
    }
}
Console.WriteLine(max);

And we have the same thing for Max:

var max = prices.Max();
Console.WriteLine(max);