How to extract a specific value from the linq query?

Question

I am building a NET 5 API and am unable to extract and calculate something. I have a table StockTransaction which among other has property Quantity (I skipped some properties for brevity):

public class StockTransaction : BaseEntity
{      
    public int Id { get; set; }
    public decimal Price { get; set; }
    public int Quantity { get; set; }
    public bool Purchase { get; set; }
    public int Resolved { get; set; }       
}

Suppose I have 7 transactions, all of which are purchase:

List<StockTransaction> list = new List<StockTransaction>
{
new StockTransaction {Id = 1, Purchase = true, Quantity = 10, Resolved = 5, Price = 50},
new StockTransaction {Id = 2, Purchase = true, Quantity = 5, Resolved = 5, Price = 70},
new StockTransaction {Id = 3, Purchase = true, Quantity = 8, Resolved = 8, Price = 25},
new StockTransaction {Id = 4, Purchase = true, Quantity = 7, Resolved = 5, Price = 77},
new StockTransaction {Id = 5, Purchase = true, Quantity = 1, Resolved = 1, Price = 23},
new StockTransaction {Id = 6, Purchase = true, Quantity = 3, Resolved = 0, Price = 14},
new StockTransaction {Id = 7, Purchase = true, Quantity = 2, Resolved = 0, Price = 17},           
};

And I would like to get the value of the last 7 quantities, which in this case gives 176 ((2 x 17) + (3 x 14) + (1 x 23) + (1 x 77)). (How) can this be done? Every help and hint is more then appreciated...

This should get you started: list .Select(s => s.Quantity * s.Price).Sum(); — Zohar Peled
– Zohar Peled, Commented Jul 15, 2021 at 8:19
I assume you know the Select() statement. It's not really clear what keeps you from getting the results you want. — Gert Arnold
– Gert Arnold, Commented Jul 15, 2021 at 8:20
Thanks, I know that part, the problem is in extracting the value of only some quantities... — Petar Sardelic
– Petar Sardelic, Commented Jul 15, 2021 at 8:21
` (3 x 14) + (1 + 23)` why is the third parenthis an addition? — Mong Zhu
– Mong Zhu, Commented Jul 15, 2021 at 8:21

Harkirat singh · Accepted Answer · 2021-07-15 09:52:44Z

1

You can use

var last3=list.OrderByDescending(x=>x.CreatedDate).Take(3).Select(x=>x.Quantity * x.Price).Sum();

var requiredSum=last3+list.Where(x=>x.id==4).Select(x=>x.Price).FirstOrDefault();

edited Jul 15, 2021 at 9:52

answered Jul 15, 2021 at 8:31

Harkirat singh

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13 Comments

Petar Sardelic Over a year ago

This is great start, but how to fetch the value of the fourth transaction and take only one quantity with the value of 77?

Harkirat singh Over a year ago

Ok modifying my answer

Harkirat singh Over a year ago

So you want values from 4th to 7 transaction only?

Petar Sardelic Over a year ago

yes, but only one quantity from the fourth transaction, and the whole 5, 6, 7 transaction

MikeT Over a year ago

you can use Skip and Take to acquire sub range of data and ElementAt to get specific records

|

SomeBody · Accepted Answer · 2021-07-15 09:13:36Z

0

Although you have tagged your question with LINQ, do it with a normal loop:

private static decimal SumOfLastTransaction(IEnumerable<StockTransaction> stockTransactions, int max)
    {
        decimal result = 0;
        int sum = 0;
        foreach(var stockTransaction in stockTransactions.OrderByDescending(x => x.Id))
        {
            
            if(sum + stockTransaction.Quantity <= max)
            {
                result += stockTransaction.Quantity * stockTransaction.Price;
                sum += stockTransaction.Quantity;
            }
            else
            {
                result += (max - sum) * stockTransaction.Price;
                return result;
            }
        }
        return result;
    }

You loop over the last items in your list. You sum the amount of transactions and check whether it is smaller than your maximum. As long as they are smaller, you can add the amount of transactions. If not, you check how much is missing until your maximum is reached and substract this from your quantity.

Online demo: https://dotnetfiddle.net/9oM4pj

edited Jul 15, 2021 at 9:13

answered Jul 15, 2021 at 8:54

SomeBody

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1 Comment

Petar Sardelic Over a year ago

this is the best answer!

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