How to use C# Linq to find average value of a double list.

Question

Hello:

I have the following data:

List<double[]> asks = new();

var ask1 = new[] { 4.0, 4.0 };

var ask2 = new[] { 5.0, 5.0 };

asks.Add(ask1);

asks.Add(ask2);

List<double[]> bids = new();

var bid1 = new[] { 3.0, 3.0 };

var bid2 = new[] { 2.0, 2.0 };

bids.Add(bid1);

bids.Add(bid2);

(List<double[]>, List<double[]>) price_data = new(asks, bids);

I want to use Linq to get the average of price.

This is how to calculate the average price:

The sum of the product of first item and the second item, divided by the sum of the second item for either asks or bids.

For example: the average price of asks = (4.0 * 4.0) + (5.0 * 5.0) / (4.0 + 5.0) = 41.0 / 9.0 = 4.55555…

the average price of bids = (3.0 * 3.0) + (2.0 * 2.0) / (3.0 + 2.0) = 2.6

So, I want to write a function, the input is the price_data, the output is (double, double) tuple with the first item being the average price of asks, and the second item for bids. The output is: (4.5, 2.6).

I know how to do this by some loops, but that seems ugly, I want to write some Linq code to make it look nice.

By the way, the double number always comes with endless number, like: 4.555555555555…

How can I limit the digit to maximum length to 10 when showing the number in screen?

Thanks,

Answer 1

@john zyd, Welcome to Microsoft Q&A, based on my test, you could use the following code to use linq to find average value of a double list.

 var result1 = from d1 in price_data.Item1
                          from d2 in price_data.Item2
                          select new
                          {
                              id1 = d1.Aggregate((x, y) => (x * y)) / d1.Count(),
                              id2 = d2.Aggregate((x, y) => (x * y)) / d1.Count(),
                              id3 = d1.Sum() / (d1.Count()*2),
                              id4 = d2.Sum() / (d2.Count()*2)
                          };
            var result2 = new Tuple<double, double>(result1.Sum(i => i.id1) / result1.Sum(i => i.id3), result1.Sum(i => i.id2) / result1.Sum(i => i.id4));

Result:

Hope my code could help you.

Best Regards,

Jack

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Answer 2

Hi,

I tried other data, the code seems not working.

But I figure out another one, it works.

But thanks for your help.

Best Regards,