LINQ using lambda syntax

Question

public class ConvertedReading
{
    public int DatePointID { get; set; }
    public string DatapointName { get; set; }
    public DateTime ReadingDate { get; set; }
    public double Value { get; set; }
}

Given a collection below:

    IEnumerable<ConvertedReading> readingData;

using c# , write a LINQ statment using lambda syntax to output a collection of the following:

public class DataPointTotal
{
    public string DatapointName{get; set;}
    public double Total{get; set;}
}

one item should be returned per datepointID

Total should reprenst the sum of convertedReading.valye relevent to each datePointID

I have tried with the following, nit quite shre if it works, i cant seems to get the sum of value right.

var subtotals = from x in ConvertedReading group x by x.DatapointName into g select new { Type = x.DatapointName , SubTotal = g.Sum(x => x.Total) };

Is the syntax correct?

Thanks guys,

var subtotals = from x in ConvertedReading group x by x.DatapointName into g select new { Type = x.DatapointName , SubTotal = g.Sum(x => x.Total) }; — Alborz
– Alborz, Commented Mar 21, 2013 at 21:44
@Alborz: Edit that into the question, and explain what's wrong with it... — Jon Skeet
– Jon Skeet, Commented Mar 21, 2013 at 21:45

Oliver · Accepted Answer · 2013-03-21 21:50:05Z

2

The answer is:

var result = readingData.GroupBy(r => r.DataPointID)
                        .Select(g => new DataPointTotal
                                {
                                    DataPointName = g.First().DataPointName,
                                    Total = g.Sum(r => r.Value)
                                });

But I guess that's cheating considering I wrote the question! ;)

answered Mar 21, 2013 at 21:50

Oliver

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3 Comments

Paul Fleming Over a year ago

Why did you ask for the answer in "lambda syntax" (actually called method syntax)? It doesn't seem fair to restrict a candidate as such...

Oliver Over a year ago

I didn't know it was called method syntax!! The questions do not all have to be completed, they are to gauge people's current knowledge base. Also, we only use "method" syntax at work as it reads better (subjective). Good on @Alborz anyway, when I don't know how to do something I also turn to the internet!

Paul Fleming Over a year ago

Yep, definately called Method Syntax. See here. There's a cool product called Technically Compatible for recruitment tests, analysis, benchmarking, and reporting. It has tens of thousands of questions like this. Plug over! :)

roman m · Accepted Answer · 2013-03-21 21:52:12Z

0

var result = db.ConvertedReading.GroupBy(i=>i.DatapointName).Select(g => new DataPointTotal(){DatapointName = g.DatapointName, Total = g.Sum(i=>i.Total)});

answered Mar 21, 2013 at 21:52

roman m

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2 Comments

Paul Fleming Over a year ago

Wrong. You can't assume that DatapointName and DataPointID are related one-to-one.

roman m Over a year ago

@flem, the code is based on the info in the question, I simply converted his code into lambda expressions w/o assuming anything :)

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