How can I find an Index in an array using a value that exists in another array and THAT array?

Question

I have a c# class that looks like this:

   public class MemberData
{
    public int meme_ck;
    public string meme_name;
    public bool meme_active;

    public MemberData(int ck2, string name2, bool active2)
    {
        meme_ck = ck2;
        meme_name = name2;
        meme_active = active2;
    }
}

I have made two arrays out of that class:

    private MemberData[] memarray1 = new MemberData[10000];
    private MemberData[] memarray2 = new Memberdata[10000];

Over the course of my application I do a bunch of stuff with these two arrays and values change, etc. Member's name or active status may change which results in the ararys becoming different.

Eventually I need to compare them in order to do things to the other one based on what results are kicked out in the first one.

For example, member is de-activated in the first array based on something application does, I need to update array 2 to de-activate that same member.

I am trying to use some database design philosphy with the int CK (contrived-key) to be able to rapidly look up the entry in the other array based on the CK.

Since I can't figure it out I've had to resort to using nested for loops like this, which sucks:

        foreach (Memberdata md in memarray1)
    {
        foreach (Memberdatamd2 in memarray2)
        {
            if (md.ck = md2.ck)
            {
                //de-activate member
            }
        }
    }

Is there a better way to do this? I just want to find the index in the second array based on CK when I have the CK value from the first array.

Any other tips or advice you have about structure would be appreciated as well. Should I be using something other than arrays? How would I accomplish this same thing with Lists?

Thanks!

You could also use: KeyedCollection<MemberData> learn.microsoft.com/en-us/dotnet/api/… — Poul Bak
– Poul Bak, Commented Aug 21, 2018 at 2:34

Eric Lippert · Accepted Answer · 2018-08-21 02:07:15Z

7

Should I be using something other than arrays?

Yes. Don't use arrays; they are seldom the right data structure to use.

How would I accomplish this same thing with Lists?

Lists are only marginally better. They don't support an efficient lookup-by-key operation which is what you need.

It sounds like what you want is instead of two arrays, two Dictionary<int, MemberData> where the key is the ck.

answered Aug 21, 2018 at 2:07

Eric Lippert

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2 Comments

john williams Over a year ago

Hey, thanks! Just out of curiosity is there a way to do the lookup within an array structure as well? I just want to learn. Thanks!

Brian Over a year ago

@johnwilliams: Array.IndexOf

Gaurang Dave · Accepted Answer · 2018-08-21 02:15:54Z

1

I totally agree with Eric Lippert's answer above. It is better you do not use Array. Same thing can be achieved using List<MemberData>. You can use LINQ as well to query your DataStructure.

Following is one of the way just to achieve your result using array

class Program
{
    static MemberData[] memarray1 = new MemberData[10000];
    static MemberData[] memarray2 = new MemberData[10000];
    static void Main(string[] args)
    {
        for (int i = 0; i < memarray1.Length; i++)
        {
            memarray1[i] = new MemberData(i + 1, "MemName" + i + 1, true);
            memarray2[i] = new MemberData(i + 1, "MemName" + i + 1, true);
        }

        // SIMULATING YOUR APP OPERATION OF CHANGING A RANDOM ARRAY VALUE IN memarray1

        int tempIndex = new Random().Next(0, 9999);

        memarray1[tempIndex].meme_name = "ChangedName";
        memarray1[tempIndex].meme_active = false;

        //FOR YOUR UDERSTADNING TAKING meme_ck IN AN INTEGER VARIABLE

        int ck_in_mem1 = memarray1[tempIndex].meme_ck;

        //FINDING ITEM IN ARRAY2

        MemberData tempData = memarray2.Where(val => val.meme_ck == ck_in_mem1).FirstOrDefault();

        // THIS IS YOUR ITEM.

        Console.ReadLine();
    }
}

answered Aug 21, 2018 at 2:15

Gaurang Dave

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1 Comment

john williams Over a year ago

Thanks! I asked Eric above as well, but is there a way to do this within the array also? Just for learning purposes. Can I use Linq in Arrays using that same code? Also I know how to find an index within an array if it matches exactly (int index = Array.IndexOf(memarray1, memarray2[i]);). Is it possible to use that somehow to look for specific fields that match instead of the entire entry having to match? Thanks again

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