CODEWITHSUNDEEP
c#linq
casillas
casillas

Reputation: 16813

Find items from the list based on given date

I have the following List item in order to display clearly. I could visualize the small list follows, that could be hundreds rows.

CourseId    ClassName    StartDate
--------    --------      --------  
12321       Math         08-25-2017 
14321       Math         08-25-2017   
32342       Physics      08-25-2017  
34345       Chemistry    08-25-2017 
25325       Math         01-25-2018
45329       Math         01-25-2018     
33325       Math         01-25-2018          
44345       Chemistry    01-25-2018

I have ClassName and Date to pass to retrieve the corresponding objects. I am having difficulty how to implement Date parameter into the LINQ. The following implementation sorts and returns only one item.

public List<Course> GetClassesByNameAndDate(string className, DateTime date, List<Courses> allCourses)
{
    List<Course> courses  = allCourses.Where( x=> x.ClassName == className && x.StartDate <= date ).OrderByDescending(x=> x.StartDate ).ToList();

}

If I pass today date and also course name as Math, then it should return me 25325,45329,33325 courseIDs objects from the list.

In other example, if I give a date 01-01-2018, then it should return 12321, 14321 objects. Because 01-01-2018 is earlier than the 25325,45329,33325 startdate which is 01-25-2018.

Upvotes: 0

Views: 68

Answers (1)

Tim Schmelter
Tim Schmelter

Reputation: 460380

I guess finally i have understood the requirement. You don't want only one item. You also don't want the list with all items where the startDate is <= date. But you want the whole group of items with the closest start-date(if all of them have the same startDate). You can GroupBy the date:

List<Course> courses  = allCourses
    .Where( x=> x.ClassName == className && x.StartDate <= date )
    .OrderByDescending(x=> x.StartDate)
    .GroupBy(x => x.StartDate)
    .FirstOrDefault()?.ToList() ?? new List<Course>();

Upvotes: 2

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