Find Value in Multidimensional Array and return all items c#

Question

here is the issue, I have an array defined like below:

int[,] Users = new int[1000,3];

Its data will be something like:

• 0,1,2
• 1,2,1
• 2,3,2
• 3,3,4
• 4,2,3 ...

the array is used as needed by my script. but I need to be able to filter the array based on one of its dimensions, and return all available matches.

For example, filtering on dimension [1], wanting all that match '3' will return an array containing:

• 2,3,2
• 3,3,4

Could anyone give me a hand with this?

Many thanks.

Answer 1

If you can change your array from int[,] to int[][] then you can easily achieve this using LINQ.

  int[][] users = new int[][]
  {
    new int[]{0,1,2},
    new int[]{1,2,1},
    new int[]{2,3,2},
    new int[]{3,3,4},
    new int[]{4,2,3}
  };


  var result = from u in users 
               where u[1] == 3 
               select u;

If changing your array is not an option then you could write a Filter function as follows.

public static IEnumerable<T[]> Filter<T>(T[,] source, Func<T[], bool> predicate)
{
  for (int i = 0; i < source.GetLength(0); ++i)
  {
    T[] values = new T[source.GetLength(1)];
    for (int j = 0; j < values.Length; ++j)
    {
      values[j] = source[i, j];
    }
    if (predicate(values))
    {
      yield return values;
    }
  }      
}

The above could then be called as follows

var result = Filter(users, u => u[1] == 3);

You could take this a step further and implement your own custom Linq extension for the Where function which would allow you to filter the T[,] arrays. Here is a naive example that could get you started.

public static class LinqExtensions
{
  public static IEnumerable<T[]> Where<T>(this T[,] source, Func<T[], bool> predicate)
  {
    if (source == null) throw new ArgumentNullException("source");
    if (predicate == null) throw new ArgumentNullException("predicate");
    return WhereImpl(source, predicate);
  }

  private static IEnumerable<T[]> WhereImpl<T>(this T[,] source, Func<T[], bool> predicate)
  {      
    for (int i = 0; i < source.GetLength(0); ++i)
    {
      T[] values = new T[source.GetLength(1)];
      for (int j = 0; j < values.Length; ++j)
      {
        values[j] = source[i, j];
      }
      if (predicate(values))
      {
        yield return values;
      } 
    }
  }    
}

With this you can again use Linq as in the first example to filter the array

  var result = from u in users 
               where u[1] == 3 
               select u;