I need to remove duplicates from a List<>

Question

I have a List<CreditCard>, a property of the credit card is CreditCardNumber, which is a string. Unfortunatly, it can be 1234 1234 1234 1234, or 1234123412341234, which are both the same number.

I need to go through and remove these duplicated items. Could someone assist?

Answer 1

using System.Linq;

public List<string> GetUniqueCardNumbers(List<string> cardNumbers)
{
    // First replace the spaces with empty strings
    return cardNumbers.Select(cc => cc.Replace(" ", ""))
                      .Distinct()
                      .ToList();
}

Answer 2

The best option would be to remove the spaces from the card number on input so you only have to perform the cleaning operation once:

    public class CreditCard: IComparable<CreditCard>
    {
        string creditCardNumberClean;
        string creditCardNumberOriginal;
        public string CreditCardNumber
        {
            get 
            { 
                return this.creditCardNumberOriginal; 
            }
            set
            {
                this.creditCardNumberOriginal = value;
                this.creditCardNumberClean = value.Replace(" ", "");
            }
        }
        public CreditCard(string creditCardNumber)
        {
            this.CreditCardNumber = creditCardNumber;
        }

        public int CompareTo(CreditCard other)
        {
            return this.creditCardNumberClean.CompareTo(other.creditCardNumberClean);
        }
    }

But if that's not possible you basically want to perform a string comparison on the card number just mutating the number to remove all spaces before the comparison:

    class Program
    {
        public static void Main(string[] args) 
        {
            List<string> list = new List<string>(new string[]{"1234 1234 1234 1234", "1234123412341234","9999 9999 9999 9999"});
            SortedSet<string> set = new SortedSet<string>(list, new CreditCardNoComparer());
            foreach (string s in set)
            {
                Console.WriteLine(s);
            }
            Console.ReadKey();
        }
    }
    public class CreditCardNoComparer : IComparer<string>
    {
        public int Compare(string x, string y)
        {
            return x.Replace(" ", "").CompareTo(y.Replace(" ", ""));
        }

    }

EDIT

//version using overridden GetHashCode and Equals methods as per @lazyberezovsky's comments 
public class CreditCard
{
    long creditCardNumberClean; //given the card number is numeric this is the most efficient way of storing it
    string creditCardNumberOriginal;
    public string CreditCardNumber
    {
        get
        {
            return this.creditCardNumberOriginal;
        }
        set
        {
            this.creditCardNumberOriginal = value;
            this.creditCardNumberClean = long.Parse(value.Replace(" ", "")); 
        }
    }
    public CreditCard(string creditCardNumber)
    {
        this.CreditCardNumber = creditCardNumber;
    }
    public override bool Equals(object obj)
    {
        CreditCard other = obj as CreditCard;
        return 
            other == null 
            ? false 
            : this.creditCardNumberClean.Equals(other.creditCardNumberClean);
    }
    public override int GetHashCode()
    {
        return this.creditCardNumberClean.GetHashCode();
    }
}

Answer 3

1. Remove white space from every one
2. Use Distinct();

Answer 4

You can create your own EqualityComparer for CreditCard which removes whitespace and use Enumerable.Distinct to remove the duplicates:

public class CardComparer : IEqualityComparer<CreditCard>
{
    private readonly Regex re = new Regex(@"\s+");

    public bool Equals(CreditCard x, CreditCard y)
    {
        return re.Replace(x.Number, "") == re.Replace(y.Number, "");
    }

    public int GetHashCode(CreditCard obj)
    {
        return re.Replace(obj.Number, "").GetHashCode();
    }
}

Then:

IEnumerable<CreditCard> unique = sourceList.Distinct(new CardComparer());

Answer 5

First you have to determine what constitutes "equal". If it's as simple as removing embedded spaces, then you can use one of the previous solutions that removes the white space and calls Distinct. Otherwise you'll have to create an equality comparer and pass it to the Distinct overload.

Answer 6

IEnumerable<CreditCard> distinctCards = cards
  .Select(card => new {
     card, 
     ccn = card.CreditCardNumber.Replace(" ", string.Empty)
  })
  .GroupBy(x => x.ccn)
  .Select(g => g.First().card) //group has at least 1 member, so First() is safe
  //.ToList()   ???

Answer 7

You can extract only the numbers from any string, in your case you can only make a replace of the space character for a empty character, for a more complex string format you can use the next code for get only numbers. You can check this answer: get only digits

string justNumbers = new String("asd123 f3 4.34-3 ".Where(Char.IsDigit).ToArray());

Then you will have only the digits of your CreditCardNumber and you can search for duplicated values.