Array of objects with custom index

Question

I have these two classes:

public class Message
{
    string Message;
    string Code;
}

public class MessageInitializer
{
    DataSet ds;
    DataRow dr;
    message[] ms;
}

I want to create a constructor in MessageInitializer like this:

MessageInitializer()
{
    this.ms = new Message[ds.Tables[0].Rows.Count];
    for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
    {
        dr = ds.Tables[0].Rows[i];
        ms[(string)dr.ItemArray[0]] = (string)dr.ItemArray[1];
    }
}

But array's index must be int type. I have no idea how to work this out:

ms[(string)dr.ItemArray[0]] = (string)dr.ItemArray[1];

Update:

Code format is a string like this: [001-001-001], so I can't convert it to integer.

What string do you have in dr.ItemArray[0]? {001-001-001]? — Nikolai Samteladze
– Nikolai Samteladze, Commented Jul 26, 2015 at 4:43
Is there a reason you want to use Array<Message> and not Dictionary<string, Message>? — Nikolai Samteladze
– Nikolai Samteladze, Commented Jul 26, 2015 at 4:46

Mohammad Chamanpara · Accepted Answer · 2015-07-26 05:48:54Z

5

you don't need Message class any more. Using a dictionary as follows solves the problem :

public class MessageInitializer
{
    DataSet ds;
    DataRow dr;
    Dictionary<string, string> ms;
    public MessageInitializer()
    {
        this.ms = new Dictionary<string,string>(ds.Tables[0].Rows.Count);
        for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
        {
            dr = ds.Tables[0].Rows[i];
            ms[(string)dr.ItemArray[0]] = (string)dr.ItemArray[1];
        }
    }
}

I hope this would be helpful.

answered Jul 26, 2015 at 5:48

Mohammad Chamanpara

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3 Comments

Nikolai Samteladze Over a year ago

Would be easier this way. Unless he wants to extend Message later by adding new properties.

Mohammad Chamanpara Over a year ago

That's right my friend. In this case using a list is the solution.

Mohammad Chamanpara Over a year ago

But as you said above the performance of the dictionaries are much better.

Nikolai Samteladze · Accepted Answer · 2015-07-26 05:51:05Z

3

If you just want to get a list of all the messages from the database, then you can use the code below. Note, List instead of Array. Easier to use and faster.

public class Message
{
    string Message;
    string Code;
}

public class MessageInitializer
{
    DataSet ds;
    DataRow dr;
    List<Message> ms;

    MessageInitializer()
    {
        this.ms = new List<Message>();
        for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
        {
            dr = ds.Tables[0].Rows[i];
            ms.Add(new Message
            {
                 Code = dr.ItemArray[0].ToString(),
                 Message = dr.ItemArray[1].ToString(),
            });
        }
    }
}

You mentioned that you have couple million records. List will perform fine in case you want to access items sequestially. If you want to access items in a non-sequential manner, I suggest you use Dictionary instead (to improve search perfromance):

public class MessageInitializer
{
    DataSet ds;
    DataRow dr;
    Dictionary<string, Message> ms;

    MessageInitializer()
    {
        this.ms = new Dictionary<string, Message>();
        for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
        {
            dr = ds.Tables[0].Rows[i];
            ms.Add(dr.ItemArray[0].ToString(), new Message
            {
                 Code = dr.ItemArray[0].ToString(),
                 Message = dr.ItemArray[1].ToString(),
            });
        }
    }
}

You can access message as follows:

var message = ms["001-001-001"];

It will be orders or magnitude faster than accessing a random List item:

var message - ms.First(x => x.Code == "001-001-001");

edited Jul 26, 2015 at 5:51

answered Jul 26, 2015 at 4:52

Nikolai Samteladze

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5 Comments

Mohammad Over a year ago

thank you so much. now how can access the single message with code? i have to use a loop. am i right?

Mohammad Over a year ago

are you sure? when I tried ms["001-001-001"] this error showed up: Error 2 Argument 1: cannot convert from 'string' to 'int'.

Nikolai Samteladze Over a year ago

My bad. I was thinking about a Dictionary. With List you can do ms.First(x => x.Code == "001-001-001").

Mohammad Over a year ago

thank you so much. i red about dictionary. seems its just what i want. please edit your post and mention dictionary in it so i can marked as answer.

Nikolai Samteladze Over a year ago

Yeah, added a sample that uses Dictionary.

A G · Accepted Answer · 2015-07-26 05:08:40Z

3

I think you just want build an array of messages from ds.Tables[0]

Code -
ms[i].Code = (string)dr.ItemArray[0];

Message -
ms[i].Message = (string)dr.ItemArray[1];

MessageInitializer()
{
    this.ms = new Message[ds.Tables[0].Rows.Count];
    for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
    {
        dr = ds.Tables[0].Rows[i];
        ms[i].Code= (string)dr.ItemArray[0];
        ms[i].Message = (string)dr.ItemArray[1];
    }
}

For better performance make use of Parallel.ForEach -

Parallel.ForEach(ds.Tables[0].AsEnumerable(), row => {
        ms[i].Code= (string)row.ItemArray[0];
        ms[i].Message = (string)row.ItemArray[1];
});

edited Jul 26, 2015 at 5:08

answered Jul 26, 2015 at 4:47

A G

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5 Comments

Mohammad Over a year ago

currently my class work exactly like this. in order to access the message in class i have a foreach and because of millions of messages in it, it works really slow. so i decided to change the class.

Nikolai Samteladze Over a year ago

@Dan do you really have to load millions of messages from you database in memory?

Mohammad Over a year ago

@AseemGautam. yes. currently it takes about 800 milliseconds to find the message and i hope i can make it faster.

Mohammad Over a year ago

@NikolaiSamteladze. unfortunately yes. i have to do it.

Nikolai Samteladze Over a year ago

@Dan do you process them somehow afterwards? If so, you might want to do it in batches (say 10000 each) not to keep such large structures in memory.

Yoan Pumar · Accepted Answer · 2015-07-26 05:29:59Z

1

I think what you want to perform is the following:

public class Message
{
    public string message { get; set; }
    public string code { get; set; }

}

public class MessageInitializer
{
    DataSet ds;
    DataRow dr;
    Message[] ms;

    MessageInitializer()
    {
        this.ms = new Message[ds.Tables[0].Rows.Count];
        for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
        {
            dr = ds.Tables[0].Rows[i];
            ms[i] = new Message
            {
                code = (string)dr.ItemArray[0],
                message = (string)dr.ItemArray[1]
            };
        }
    }
}

answered Jul 26, 2015 at 5:29

Yoan Pumar

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1 Comment

Yoan Pumar Over a year ago

Dan, to find a single message by code, you ca use: var myMessage = ms.SingleOrDefault(item => item.code == someCode);

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