How to compare arrays in a list

Question

I have a List contains arrays in various sizes. For example:

enter image description here

0 and 7. arrrays have same data {1,2,3,4,5,6}
2, 4 and 5. arrays have same data {1,2,3}
Attention! 3 and 6 doesn't have same data [3] = {1,2} , [6] = {1,3}

I want to get which indexes have same data and add this indexes to another List. For example

anotherList[ 0 ] = {0,7}

anotherList[ 1 ] = {2,4,5}

How can I do this?

Thanks in advance.

I imagine you would loop through your list, with a nested loop through the other elements in the list, comparing each element and adding indexes to another list each time the comparison found a match. The comparison itself would be a method which accepts two arrays and determines if they're "equal" by the logic you've defined. Have you made any attempt at this? — David, Dec 27 '13 at 14:35
http://stackoverflow.com/questions/713341/comparing-arrays-in-c-sharp — vborutenko, Dec 27 '13 at 14:35
You want to make a new `List` that `contains` the values requested; e.g. `anotherList[0] = {0,7}` will return a new `List` that tells you which `List` `contains` both `0` and `7`??? — KSdev, Dec 27 '13 at 14:35
To simplify the code i would suggest to have a look at the ISet Implementations like HashSet with method to compare items for example Intersect wich returns the items contained in both lists http://msdn.microsoft.com/de-de/library/vstudio/bb918911%28v=vs.90%29.aspx — Boas Enkler, Dec 27 '13 at 14:41

score 1 · Accepted Answer · answered Dec 27 '13 at 14:47

You can use this code (Linq i.e. SequenceEqual is very helpful here):

    private static IList<IList<int>> EqualArrays(List<int[]> list) {
      IList<IList<int>> result = new List<IList<int>>();

      HashSet<int> proceeded = new HashSet<int>();

      for (int i = 0; i < list.Count; ++i) {
        if (proceeded.Contains(i))
          continue;

        int[] item = list[i];
        List<int> equals = new List<int>() { i };

        result.Add(equals);

        for (int j = i + 1; j < list.Count; ++j)
          if (item.SequenceEqual(list[j])) {
            equals.Add(j);
            proceeded.Add(j);
          }
      }

      return result;
    }


   ...

   // Your test case:
   List<int[]> list = new List<int[]>() {
     new int[] {1, 2, 3, 4, 5, 5, 7},
     new int[] {1},
     new int[] {1, 2, 3},
     new int[] {1, 2},
     new int[] {1, 2, 3},
     new int[] {1, 2, 3},
     new int[] {1, 3},
     new int[] {1, 2, 3, 4, 5, 5, 7}
   };

   // anotherList == {{0, 7}, {1}, {2, 4, 5}, {3}, {6}}
   IList<IList<int>> anotherList = EqualArrays(list);

score 0 · Answer 2 · answered Dec 27 '13 at 14:38

0

Try this

List<byte[]> anotherList = new List<byte[]>();
foreach (byte[] array in list2)
    if (!list1.Any(a => a.SequenceEqual(array)))
        anotherList.Add(array);

answered Dec 27 '13 at 14:38

Vignesh Kumar A

27,863
13
63
115

score 0 · Answer 3 · edited May 23 '17 at 12:11

int[][] original =
{
    new [] {1,2,3,4,5,6},
    new [] {1},
    new [] {1,2,3},
    new [] {1,2},
    new [] {1,2,3},
    new [] {1,2,3},
    new [] {1,3},
    new [] {1,2,3,4,5,6},
};

int[][] anotherList =
    original.Select((values, index) => new { values, index })
            .GroupBy(x => x.values, SequenceComparer<int>.Default)
            .Where(grouping => grouping.Count() > 1)   // optional
            .Select(grouping => grouping.Select(x => x.index).ToArray())
            .ToArray();

I've adapted the definition for SequenceComparer<T> from here (and here):

public class SequenceComparer<T> : IEqualityComparer<IEnumerable<T>>
{
    public static readonly SequenceComparer<T> Default = new SequenceComparer<T>();

    public bool Equals(IEnumerable<T> x, IEnumerable<T> y)
    {
        if (Object.ReferenceEquals(x, y))
            return true;

        return x != null && y != null && x.SequenceEqual(y);
    }

    public int GetHashCode(IEnumerable<T> seq)
    {
        if (seq == null)
            return 0;

        unchecked
        {
            const int p = 16777619;
            const int hash = (int)2166136261;

            return seq.Select(e => e.GetHashCode())
                      .Aggregate(hash, (a, b) => (a ^ b) * p));
        }
    }
}

In what assembly or namespace is the `SequenceComparer` stored? — Ondrej Janacek, Dec 27 '13 at 14:55
@OndrejJanacek: Edited answer to include definition and source. — Douglas, Dec 27 '13 at 15:00
I thought you made that up. I'm not aware of such a thing within .NET. — Ondrej Janacek, Dec 27 '13 at 15:02

How to compare arrays in a list

3 Answers3