Implementing [ ] operator

Question

I have implemented the "[ ]" operator in a class that I have created to return values associated with a key (the same concept of a dictionary, except that it's possible to have the same key more than one time). However, looking at my code I don't think it is as efficient as it could be.

public class MyClass
{
    public object[][] Values;

    public MyClass()
    {
        Values = new object[4][];
    }

    public IEnumerable<object> this[string key]
    {
        get
        {
            var results = new List<object>();

            foreach (var value in this.Values)
            {
                if (value[0].ToString() == key)
                {
                     results.Add(value[1]);
                }
             }

            return results;
        }
    }
}

Values can contain a bunch of 2 values arrays.

A small example:

MyClass class = new MyClass();

class.Values[0] = new object[] { "key1", 25 };
class.Values[1] = new object[] { "key2", 3 };
class.Values[2] = new object[] { "key2", 789 };
class.Values[3] = new object[] { "key4", 12 };

and when I do class["key2"], it returns a collection containing 3 and 789.

What do you think of the way I implemented the this[string key] method? Do you think there is a way to do this without iterating on all the objects in the Values array?

Read about Generics (msdn.microsoft.com/en-US/library/ms379564.aspx) and favor them over storing items of type object. — Jesse C. Slicer
– Jesse C. Slicer, Commented Jul 10, 2012 at 13:25

svick · Accepted Answer · 2012-07-10 14:59:13Z

10

If you look for performance, you'd better rely on the framework dictionary. You can use the Dictionary<string, List<object>> to do what you need. When you add a new key and value, look if the key already exists. If so, add the value to the array and don't add the key.

edited Jul 10, 2012 at 14:59

svick

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answered Jul 10, 2012 at 13:14

Amiram Korach

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1

\$\begingroup\$ I think you mean Dictionary<string, List<object>>. \$\endgroup\$

svick
– svick

2012-07-10 14:14:17 +00:00
Commented Jul 10, 2012 at 14:14
\$\begingroup\$ Yes you're right. Thanks. How do I accept your edit? \$\endgroup\$

Amiram Korach
– Amiram Korach

2012-07-10 14:16:41 +00:00
Commented Jul 10, 2012 at 14:16
\$\begingroup\$ I didn't propose that edit, you could have just edited your answer by yourself. (I have enough reputation on this site, so that my edits are accepted automatically. If I didn't and I made that edit, you would see a number beside the “edit” button, signifying how many people already accepted the edit.) \$\endgroup\$

svick
– svick

2012-07-10 15:01:24 +00:00
Commented Jul 10, 2012 at 15:01

Add a comment |

Bill Barry · Accepted Answer · 2012-07-10 22:01:46Z

This is intended as a comment to the answer from @AmiramKorach; here is a reasonable way to get from the list you have to the dictionary you want (without concerning yourself about managing the dictionary details):

Dictionary<string, List<int>> result =
    new[]
        {
            new {Name = "key1", Value = 25},
            new {Name = "key2", Value = 3},
            new {Name = "key2", Value = 789},
            new {Name = "key3", Value = 12}
        }
        .GroupBy(p => p.Name)
        .ToDictionary(
            group => group.Key,
            values => values.Select(g => g.Value).ToList()
        );

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