Solved

c# Linq, List, GroupBy or Distinct and max(date)

Posted on 2014-01-26
2
5,599 Views
Last Modified: 2016-02-10
With this example of a List (weatherforecast )- Week Day, Local, Weather, Temp, Forecast Date)

"Tuesday", "Lisbon", "good", "19", "24-Jan-14 "  -----> ok
"Friday", "Lisbon", "cloudy", "20", "24-Jan-14 "  -----> ok
"Sunday", "Troia", "good", "20", "24-Jan-14 "   -----> ok
"Tuesday", "Lisbon", "good", "18", "22-Jan-14"
"Friday",  "Praia Verde, "excellent", "20", "22-Jan-14" -----> ok
"Sunday", "Troia", "good", "20", "22-Jan-14"

I want the latest forecasts (4 rows here) so I need to use  max(date) somewhere.  The max(date) may not be all equal.

For Lisbon and Troia I will have only 24 Jan, but for "Praia Verde" I will have the 22 Jan.

I want to put in a grid all results that are wit ----> ok

Struggling with this! Tks for any help
0
Comment
Question by:novreisb
2 Comments
 
LVL 23

Accepted Solution

by:
Ioannis Paraskevopoulos earned 500 total points
ID: 39811612
Hi,

Check my example:

void Main()
{
        // Initialization of the list
	List<WeatherForeCast> WeatherForeCastList = new List<WeatherForeCast>()
	{
		new WeatherForeCast(){WeekDay = "Tuesday",Local = "Lisbon", Weather = "good", Temp = 19, ForeCastDate = DateTime.Parse("24-01-2014")},
		new WeatherForeCast(){WeekDay = "Friday",Local = "Lisbon", Weather = "cloudy", Temp = 20, ForeCastDate = DateTime.Parse("24-01-2014")},
		new WeatherForeCast(){WeekDay = "Sunday",Local = "Troia", Weather = "good", Temp = 20, ForeCastDate = DateTime.Parse("24-01-2014")},
		new WeatherForeCast(){WeekDay = "Tuesday",Local = "Lisbon", Weather = "good", Temp = 18, ForeCastDate = DateTime.Parse("22-01-2014")},
		new WeatherForeCast(){WeekDay = "Friday",Local = "Praia Verde", Weather = "excellent", Temp = 20, ForeCastDate = DateTime.Parse("20-01-2014")},
		new WeatherForeCast(){WeekDay = "Sunday",Local = "Troia", Weather = "good", Temp = 20, ForeCastDate = DateTime.Parse("22-01-2014")},
	};
	

        //This will get the required results
	WeatherForeCastList
        //First group by region (Local)
	.GroupBy
	(
		x=>x.Local
	)
        //From the group, only select those rows, that have a ForecastDate equal to the max ForecastDate of each group. This will create a list of lists of WeatherForeCast class (check the following screenshot to see how they look in LinqPad.
	.Select
	(
		x=>
		x
		.Where
		(
			z=>
			z.ForeCastDate == x.Max (d => d.ForeCastDate)
		)
		.Select 
		(
			z => new WeatherForeCast
				{
					WeekDay=z.WeekDay,
					Local = z.Local,
					Weather = z.Weather,
					Temp = z.Temp,
					ForeCastDate = z.ForeCastDate
				}
		)
	)
        //The following is necessary in order to get only one flat list of WeatherForeCast objects
	.SelectMany 
	(
		x => x
	);
}

public class WeatherForeCast
{
    public string WeekDay {get;set;}
    public string Local{get;set;}
    public string Weather {get;set;}
    public int Temp{get;set;}
    public DateTime ForeCastDate{get;set;}
}

Open in new window


GroupBySelectSelectMany
0
 

Author Closing Comment

by:novreisb
ID: 39812994
Hi jyparask,

My instinct pointed to a GroupBy  with two variables (Local, Weekday) but the results shows what I want. Thank you very much!

Luis
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
bank transaction downloader ? 1 67
c#, linq to sql 4 69
Filter data object using LINQ? 5 71
Dialogbox API leak? 18 81
The way I use Experts Exchange to assist me in analyzing and diagnosing a problem is I first enter a Verbose Question at Experts Exchange like: Office 2007 will hang when opening and saving files I then launch WordPad (any text editor will do) an…
After several hours of googling I could not gather any information on this topic. There are several ways of controlling the USB port connected to any storage device. The best example of that is by changing the registry value of "HKEY_LOCAL_MACHINE\S…
Windows 8 comes with a dramatically different user interface known as Metro. Notably missing from the new interface is a Start button and Start Menu. Many users do not like it, much preferring the interface of earlier versions — Windows 7, Windows X…
In this video, we discuss why the need for additional vertical screen space has become more important in recent years, namely, due to the transition in the marketplace of 4x3 computer screens to 16x9 and 16x10 screens (so-called widescreen format). …

920 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

16 Experts available now in Live!

Get 1:1 Help Now