Compare a property of an object in 2 lists

Question

I have the following (simplified) class:

public class CareRate {

  [Key]
  public int Id { get; set; }
  public string Description { get; set; }
  public decimal DayRate { get; set; }
}

I would like to compare two lists of CareRate only by their DayRate; one with CareRates containing the current DayRates and one with CareRates containing the DayRates to update. Other properties which might have changed like Description, should not be taken into account.

// Just a test method
public List<CareRate> FilterChangedCareRates(){
    var currentCareRates = new List<CareRate>{
        new CareRate { Id = 1, DayRate = 3,33, Description = "Some descr" }, 
        new CareRate { Id = 2, DayRate = 4,44, Description = "Some other descr" } 
    };

    var updatedCareRates = new List<CareRate>{
        new CareRate { Id = 1, DayRate = 2,22 }, 
        new CareRate {Id = 2, DayRate = 4,44 } // Unchanged
   };

    var actualUpdatedCareRates = new List<CareRate>();

    foreach(var updatedCareRate in updatedCareRates) {
        var currentCareRate = currentCareRates.Single(x => x.Id == updatedCareRate.Id); 
        if (updatedCareRate.DayRate != currentCareRate.DayRate) {
            actualUpdatedCareRates.Add(updatedCareRate); 
        }
    }
    return actualUpdatedCareRates;
}

The manner to filter the changed CareRate objects by Dayrate, feels a bit devious. I think I am overlooking something. What other and better options are there for acquiring the above?

Im not entirely sure what you want to do with the lists you speak of.. are you just after a list of items where the rate changed, or an updated list of all the original items wth new rates? — BugFinder, Nov 07 '17 at 13:44
Seems like a review. Should probably go to CodeReview.StachExchange.com — MakePeaceGreatAgain, Nov 07 '17 at 13:45
@BugFinder would like to have a new list of CareRate that only have a changed DayRate (compared to the current DayRate). — Melissa, Nov 07 '17 at 13:46
You can do this in one line: `return updatedCareRates.Where(updated => currentCareRates.Any(current => current.DayRate != updated.DayRate))`. — dbraillon, Nov 07 '17 at 13:47
@HimBromBeere Codereview.stackexchange.com, yes. The non-simplified version would be preferred over there, please refer to the [help center](https://codereview.stackexchange.com/help/on-topic). — Mast, Nov 07 '17 at 13:55
@S.Akbari I have posted an answer. I created a comparer to use in the `Except` extension method. — Melissa, Nov 08 '17 at 12:01

Salah Akbari · Accepted Answer · 2017-11-07T15:41:41.077

1

Simply use Zip method in LINQ:

var actualUpdatedCareRates = currentCareRates.Zip(updatedCareRates, 
                             (f, s) => f.DayRate != s.DayRate ? s : null)
                             .Where(c => c != null).ToList();

edited Nov 07 '17 at 15:41

answered Nov 07 '17 at 14:05

Salah Akbari

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score 0 · Answer 2 · edited Nov 07 '17 at 20:35

I think, you can use something like this:

updatedCareRates.ForEach(x =>
{
    if (currentCareRates.FirstOrDefault(y => y.Id == x.Id && y.DayRate != x.DayRate) != null)
        actualUpdatedCareRates.Add(x);
});

Or in one line:

updatedCareRates.Where(x => currentCareRates.FirstOrDefault(y => y.Id == x.Id &&
                            y.DayRate != x.DayRate) != null).ToList()
                           .ForEach(x => actualUpdatedCareRates.Add(x));

PinBack · Answer 3 · 2017-11-07T14:53:15.950

0

You can use this:

return (from up in updatedCareRates
            join cur in currentCareRates
            on up.Id equals cur.Id
            where up.DayRate != cur.DayRate
            select up).ToList();

Here is one of the rare cases where I think Query syntax is better than Method syntax.

edited Nov 07 '17 at 14:53

answered Nov 07 '17 at 14:23

PinBack

2,499
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score 0 · Answer 4 · edited Nov 08 '17 at 20:37

Instead of using an Where(x => x...), I looked for a solution with using the Except method as posted here.

I created a class DayRateComparer as showed below.

public class DayRateComparer : IEqualityComparer<CareRate>
{
    public bool Equals(CareRate x, CareRate y) {
        if (x = null) throw new ArgumentNullException(nameof(x));
        if (y = null) throw new ArgumentNullException(nameof(y));

        return x.Id == y.Id && x.DayRate == y.DayRate;
    }

    public int GetHashCode(CareRate obj) {
        retun obj.Id.GetHashCode() + obj.DayRate.GetHashCode(); 
    }
}

And I used the DayRateComparer like this:

// Just a test method
public List<CareRate> FilterChangedCareRates(){
    var currentCareRates = new List<CareRate>{
        new CareRate { Id = 1, DayRate = 3,33, Description = "Some descr" }, 
        new CareRate { Id = 2, DayRate = 4,44, Description = "Some other descr" } 
    };

    var updatedCareRates = new List<CareRate>{
        new CareRate { Id = 1, DayRate = 2,22 }, 
        new CareRate {Id = 2, DayRate = 4,44 } // Unchanged
   };

    return updatedCareRates.Except(currentCareRates, new DayRateComparer()).ToList();
}

I don't like the use of a temporary list (like actualUpdatedCareRates) and this is not necessary anymore when using a comparer. The Zip method as mentioned by @S.Akbari is also a clean and short way but looks a bit complex for me at first sight. Thanks all for your posts.

No `Zip` is not complex as you think. Just go and read how does it works in the link that I've mentioned in my answer. It makes your works a lot easier than writing a comparer for this purpose while you can easily use `Zip` method IMO. — Salah Akbari, Nov 08 '17 at 12:04
@S.Akbari, you are right. It isn't that complex and it does what it should do. I marked your answer as the solution. — Melissa, Nov 10 '17 at 11:51

Compare a property of an object in 2 lists

4 Answers4