Linq计算集合中列表的差异数

Question

I want to count the number of differences (or similarities) in lists within a collection.The following code is a for loop which produces the right results, comparing every other record with the first record. Is there a way to do it better? With Linq, perhaps?

public void Main(){
        _records = new ObservableCollection<Record>();
        _records.Add(new Record { Name = "Correct", Results = new List<string> { "A", "B","C" } , Score="100%"} );
        _records.Add(new Record { Name = "John", Results = new List<string> { "A", "B" ,"C" } } ); //Expect score to be 3/3  (100%)
        _records.Add(new Record { Name = "Joseph", Results = new List<string> { "A", "C","B" } }); //Expect score to be 2/3 (67%)
        _records.Add(new Record { Name = "James", Results = new List<string> { "C", "C", "C" } }); //Expect score to be 1/3 (33%)

        for(int i = 1; i < _records.Count(); i++) // Each Results in the _records except "Correct"
        {
            float score = _records[0].Results.Count();
            _records[i].Score = string.Format("{0:p1}", (score - CountDifferences(_records[i].Results, _records[0].Results) )  / score );
        }


}

private int CountDifferences(List<string> x, List<string> y)
{
    return (x.Zip(y, (a, b) => a.Equals(b) ? 0 : 1).Sum());
}

Answer 1

I would go about doing it like this:

var results =
    from r0 in _records.Take(1)
    from r in _records
    let score = (double)r0.Results.Count()
    let differences = CountDifferences(r.Results, r0.Results)
    select new { record = r, score = ((score - differences) / score).ToString("p1") };

foreach (var result in results)
{
    result.record.Score = result.score;
}

I would, hovever suggest that you do not have .Score as a property of Record as a score is only valid when you can compare one record against another. That would mean that if you have three separate results the score could be different if you compare against either of the other two.

So I would suggest this:

public class Record
{
    public string Name;
    public List<string> Results;
    public double GetScore(Record benchmark)
    {
        var max = benchmark.Results.Count;
        var differences = benchmark.Results
            .Zip(this.Results, (a, b) => a == b)
            .Where(r => r == false)
            .Count();
        return ((double)max - differences) / max;
    }
}

Then just do this query to get the results:

var results =
    from r0 in _records.Take(1)
    from r in _records
    select new
    {
        record = r,
        score = r.GetScore(r0).ToString("p1")
    };

That gives me:

Answer 2

I made the LINQ (with lambda expressions) statement work off a dictionary that uses the students' name as the key and custom class Record as the value. Then compare that against a separate List the grades are expected to be.

List<string> expected = new List<string>(){"A", "B","C" };
Dictionary<string, Record> _records = new Dictionary<string, Record>();
_records["John"] = new Record { Name = "John", Results = new List<string> { "A", "B" ,"C" } } ;
_records["Joseph"]= new Record { Name = "Joseph", Results = new List<string> { "A", "C","B" } } ;
_records["James"] = new Record { Name = "James", Results = new List<string> { "C", "C", "C" } } ;

foreach(var v in _records){
    decimal count = v.Value.Results.Where((x,index) => expected[index]==x).Count()/(decimal)expected.Count();
    v.Value.Score = String.Format("{0:P0}",count);
}

foreach(var v in _records)
    Console.WriteLine("{0} {1}",v.Value.Name,v.Value.Score);