Determine if Dictionary Contains All of a Set of Keys

Question

I'm trying to figure out the best way to determine if a Dictionary<string, string> object contains all of a set of string objects as keys.

I'm probably not making any sense so here's some example code using a definite set of strings:

public static bool ContainsKeys(this Dictionary<string, string> dictionary)
{
  return dictionary.ContainsKey("fname") && dictionary.ContainsKey("lname") && dictionary.ContainsKey("address1") &&
         dictionary.ContainsKey("city") && dictionary.ContainsKey("state") && dictionary.ContainsKey("zip");
}

The idea here is to accept an arbitrary set of strings as keys and check if the keys of the Dictionary<string, string> object contain all of the strings in keys.

I was trying to go down the LINQ road with this:

public static bool ContainsKeys(this Dictionary<string, string> dictionary, string[] keys)
{
  var query = from entry in dictionary
              where keys.Contains(entry.Key)
              select entry;

  return query.Any();
}

I have no idea if I'm on the right path though - I think this might work if I wanted to know if dictionary contained any of those strings as keys.

Answer 1

Something like this should meet your requirement. Apply proper validations around your arguments, of course.

return keys.Any() 
    && keys.All(key => dictionary.ContainsKey(key));

Note: I include Any because All will return true if the source sequence (keys) is actually empty. If you don't mind this, then eliminate the use of Any.

Answer 2

This can be done pretty simply using the All extension method.

return keys.All(k => dictionary.ContainsKey(k));

This will check that the given predicate (dictionary.ContainsKey(k)) is true for all keys in the given array.

Answer 3

LINQ is indeed good for this sort of thing:

public static bool ContainsKeys(this Dictionary<string, string> dictionary, string[] keys)
{
  return keys.All(dictionary.ContainsKey);
}