在 LINQ 中的列表中获取列表中的最大值

Question

Here's my code:

public class Calculation
{
    public int Id;
    public string ErrorCode;
    public ICollection<CalculationDetails> CalculationDetails;
}

public class CalculationDetails
{
    public int Id;
    public decimal? Amount;
    public decimal? Rate;
    public string Category;
}

public static Category
{
    public const string CategoryA = "A";
    public const string CategoryB = "B";
}

I am having a list of calculations in the object List<Calculation> calculations .

I want to fetch the maximum of Amounts of Category B from Calculations object.

Answer 1

List<Calculation> calculations = ...

Decimal max = calculations
    .Where( c => c != null )
    .SelectMany( c => c.CalculationDetails )
    .Where( cd => cd != null )
    .Where( cd => cd.Category == Category.CategoryB )
    .Select( cd => cd.Amount ?? 0 )
    .DefaultIfEmpty( 0 )
    .Max();

Feel free to elide the .Where( x => x != null ) if you're confident there are no nulls.

Answer 2

Try this:

var calculations = new List<Calculation>(); //pretend it's filled

var maxAmountCategoryB = calculations
    .SelectMany(c => c.CalculationDetails)
    .Where(d => d.Category == Category.CategoryB)
    .Max(d => d.Amount.GetValueOrDefault());

Answer 3

You could use

var result = listOfCalculation.Max(x=>x.CalculationDetails
                                  .Where(c=>c.Category.Equals(Category.CategoryB))
                                  .Max(c=>c.Amount));

Demo Code