How to get the array of values out of an indexer?

Question

I'm using a class that has an indexer defined and would like to get the data out of it and into a simple array. Is there a better way than looping through the indexer?

The indexer:

public class MyIndexer
{
    public int Foo { get; }
    public int GetSize{ get; }  //size of data vector
    public float this[int idx] { get; set; }
}

Something like this would be nice:

float[] data = indexer.GetData();

Note that I can't change MyIndexer.

Does the class have anything else provided, like IEnumerable, a float[] getData method, anything? I'm assuming no since you're trying this, but that would be the simplest manner. If it doesn't, are there any other methods that could help? — ssube
– ssube, Commented Aug 17, 2012 at 18:26
As @peachykeen implied, there's really not enough info here to give a good answer. If the public properties/methods/interfaces for the class are really as nondescript as your example, there's no way to know how to get every value, or if such a thing is even logically possible (e.g. maybe the indexer is defined such that it just returns i++, where i is a private int field). — Tim S.
– Tim S., Commented Aug 17, 2012 at 18:30
There isn't anything in the class apart from that. But I know that the data is data acquired from a sound card - I think it#s just an array of floats stuffed into an indexer to bundle that data with the meta data like the size of the array. All I want is to parse that indexer to an array to be able to stuff that data into the DB. — mort
– mort, Commented Aug 17, 2012 at 18:33

Lee · Accepted Answer · 2012-08-17 18:42:18Z

1

Since you can get the number of elements, you can create an extension method:

public static float[] GetData(this MyIndexer indexer)
{
    return Enumerable.Range(0, indexer.GetSize).Select(i => indexer[i]).ToArray();
}

You could also just use a for loop:

public float[] GetData(this MyIndexer indexer)
{
    float[] data = new float[indexer.GetSize];
    for(int i = 0; i < data.Length; i++)
    {
        data[i] = indexer[i];
    }
}

edited Aug 17, 2012 at 18:42

answered Aug 17, 2012 at 18:36

Lee

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2 Comments

mort Over a year ago

That works, but is it actually performing better (or considered a better practice than) just iterating over the indexer and storing the values to an array? This is fancy technology-wise, but not easy to read.

Lee Over a year ago

@mort - The LINQ solution will be slightly slower than manually creating the array and populating the data with a for loop, so I added that as well.

Guffa · Accepted Answer · 2012-08-17 18:47:39Z

1

No, there is no other way than to loop through the indexes. There are many ways to do the looping, but no way around it.

Also, looping through the indexes only works if the indexer actually can return values for the indexes that you expect it to. Just because the class has an indexer doesn't mean that it has to be implemented to handle any specific indexes.

answered Aug 17, 2012 at 18:47

Guffa

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Comments

Jon Hanna · Accepted Answer · 2012-08-17 19:08:37Z

0

From what you have there, looping would be the only way.

I'd be pretty annoyed at the developer of the class though. There are conventions in .NET that are backed up by well known interfaces; ICollection, ICollection<T>, IList, IList<T> being particularly apt.

While arrays and string's use of Length is a near-exception, the only reason I can think of for calling GetSize, "GetSize" (or indeed, for calling a property anything in the form "GetXXX") is if I knew the person who would be using the class, and I really disliked them. Not implementing ICollection<float> is a bit more likely to be justifiable, but it still is something to justify with a good reason, rather than just not bothering.

Since most classes of this nature would implement ICollection<float>, in most cases where this comes up you'd be able to do:

float[] arr = new float[indexer.Count];
indexer.CopyTo(arr, 0);

But most bizarre still is the fact that it doesn't even implement IEnumerable<float>. That's really, really weird. It's such a core part of .NET ways of doing things, that unless there's a really good reason, it's bordering on being a bug-of-omission. If it had, then you could have just done index.ToArray().

If I had to work with this object much, I'd probably write a wrapper class or at least a set of extension methods to fill in the gaps.

answered Aug 17, 2012 at 19:08

Jon Hanna

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2 Comments

mort Over a year ago

I think the main reason for the developer not following .NET conventions is that he is a C++ guy and the indexer actually wraps a C++ object...

Jon Hanna Over a year ago

Well, you could at least tell him about how to C++ .NET properties become get_ and set_ and he might desist from get_GetXXX!

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