c# how to retrive objects as values from array

Question

I am trying to create a simple 'inventory' system that stores items with the key being an items name, and with the remaining information being stored as a value. However, I am having difficulty figuring out how to then read the information. For example, if I have say a list of 10 items, and I want to select the items 'type' information from the key 'television' outlined below, how could I do this?

television {large, 5, 3, false, dynamic, 0.8, 20}

Hashtable myItems = new Hashtable();    

protected virtual bool OnAttempt_AddItem(object args) {
            object[] arr = (object[])args;
            string ItemType = (string)arr[0];
            string ItemName = (string)arr[1];
            int ItemAmount = (arr.Length == 2) ? (int)arr[2] : 1;
            int ItemACanHave = (arr.Length == 3) ? (int)arr[3] : 1;
            bool ItemClear = (bool)arr[4];
            string ItemEffect = (string)arr[5];
            float ItemModifier = (float)arr[6];
            int ItemWeight = (int)arr[7];

            // enforce ability to have atleast 1 item of each type
            ItemACanHave = Mathf.Max(1, ItemACanHave);

            myItems[ItemName] = new object[] {ItemType, ItemAmount, ItemACanHave, ItemClear, ItemEffect, ItemModifier, ItemWeight };    

            return true;    
        }

Is there any reason you're still using the non-generic Hashtable collection instead of Dictionary<,>? (It sounds like you should be creating an Item class to encapsulate all of these values btw.) — Jon Skeet
– Jon Skeet, Commented May 13, 2013 at 8:25
Haven't used HashTable, however is there any concern using a self-defined entity class? — Fendy
– Fendy, Commented May 13, 2013 at 8:26
I'm fairly new to C# and its array types. If there's a better method I'd greatly appreciate it if someone could introduce me to it. — Keiran Lovett
– Keiran Lovett, Commented May 13, 2013 at 8:28
Are you familiar with OOP? Define class for your item and use generic Dictionary<string,yourclasstype> to created well-structured and fast enough data entity. — Tommi
– Tommi, Commented May 13, 2013 at 8:30

Alex Filipovici · Accepted Answer · 2013-05-13 09:10:52Z

1

Create an item class to encapsulate the properties:

public class InventoryItem
{
    public string Name;
    public string Type;
    public int Amount;
    public int CanHave; // you should consider renaming this - it's very unclear what this could mean
    public bool Clear;
    public string Effect;
    public float Modifier;
    public int Weight;
}

Then you can use a Dictionary to store items:

Dictionary<string, InventoryItem> inventory = new Dictionary<string, InventoryItem>();

inventory["television"] = new InventoryItem 
                                { 
                                     Name = "television", Type = "large", Amount = 5,
                                     CanHave = 3, Clear = false, Effect = "dynamic",
                                     Modifier = 0.8, Weight = 20
                                });

And you can look it up like this:

Console.WriteLine("Type of television is: ", inventory["television"].Type);

edited May 13, 2013 at 9:10

Alex Filipovici

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answered May 13, 2013 at 8:35

ChrisWue

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5 Comments

JleruOHeP Over a year ago

you forgot about key in your inventory.Add

Tommi Over a year ago

Just curious - is there any advantages to use field against auto-property in your class?

ChrisWue Over a year ago

@Tommi: It depends what it is being used for. You can always refactor it later.

Keiran Lovett Over a year ago

Trying this method I get an error - error CS1525: Unexpected symbol [', expecting identifier'

Tommi Over a year ago

This is because of typo I mentioned above. Indexer should not be separated with comma, replace inventory.["television"] with inventory["television"]

Alex Filipovici · Accepted Answer · 2013-05-13 09:26:40Z

I would suggest you to consider the possibility of more than one item of a certain type in a inventory list, i.e. two or more television sets instead of only one.

Use a base class and derived classes:

public class InventoryItem
{
    public string ItemType { get; set; }
    public string ItemName { get; set; }
    public int ItemAmount { get; set; }
    public int ItemACanHave { get; set; }
    public bool ItemClear { get; set; }
    public string ItemEffect { get; set; }
    public float ItemModifier { get; set; }
    public int ItemWeight { get; set; }
}

public class Radio : InventoryItem
{
}

public class Television : InventoryItem
{
}

// TODO: add your derived classes

Use a List<InventoryItem> to store the collection:

List<InventoryItem> InventoryItems = new List<InventoryItem>();

Modify your method (don't forget to add exception handling, as sometimes you might get different input than the one you expected in the args object):

protected virtual bool OnAttempt_AddItem(object args)
{
    // TODO: handle unboxing exceptions, size of the array etc
    //
    try
    {
        object[] arr = (object[])args;
        switch (arr[0].ToString().ToLower())
        {
            // TODO: add other types (Radio etc)
            case "television":
                var tv = new Television();
                tv.ItemType = (string)arr[0];
                tv.ItemName = (string)arr[1];
                tv.ItemAmount = (arr.Length == 2) ? (int)arr[2] : 1;
                tv.ItemACanHave = (arr.Length == 3) ? (int)arr[3] : 1;
                tv.ItemClear = (bool)arr[4];
                tv.ItemEffect = (string)arr[5];
                tv.ItemModifier = (float)arr[6];
                tv.ItemWeight = (int)arr[7];

                // enforce ability to have atleast 1 item of each type
                tv.ItemACanHave = Math.Max(1, tv.ItemACanHave);
                InventoryItems.Add(tv);
                break;
            default:
                var genericItem = new InventoryItem();
                genericItem.ItemType = (string)arr[0];
                genericItem.ItemName = (string)arr[1];
                genericItem.ItemAmount = (arr.Length == 2) ? (int)arr[2] : 1;
                genericItem.ItemACanHave = (arr.Length == 3) ? (int)arr[3] : 1;
                genericItem.ItemClear = (bool)arr[4];
                genericItem.ItemEffect = (string)arr[5];
                genericItem.ItemModifier = (float)arr[6];
                genericItem.ItemWeight = (int)arr[7];

                // enforce ability to have atleast 1 item of each type
                genericItem.ItemACanHave = Math.Max(1, genericItem.ItemACanHave);
                InventoryItems.Add(genericItem);
                break;
            //handle other cases
        }
        return true;
    }
    catch (Exception ex)
    {
        // log the error
        return false;
    }
}

Retrieve the filtered items like this:

var largeTvType = inventory.InventoryItems.OfType<Television>()
    // filter by type (or other criteria)
    .Where(tv => tv.ItemType == "large")
    // select only the property your interested in (in the case below
    // it will be always "television" because that's part of the 
    // logic inside the OnAttempt_AddItem method's switch statement)
    .Select(tv => tv.ItemType);

Still, as ChrisWue suggested in his answer, if you know that your inventory lists will be very large, I'd recommend you to use a Dictionary<string, InventoryItem>, the string key being a unique inventory item identifier. It will be faster.

Could I get an explanation of the differences between this method and @ChrisWue ?
The main difference is using List instead of Dictionary. I don't think it's a good idea if you want to get items by key. Dictionary lookup complexity is O(1) while LINQ query will be O(n) in common case. Also, you still can use LINQ on .Values member of Dictionary, if you'll need to.
There are two perspectives over what you want to achieve. I believe that both of us gave you some examples based on some of our own assumptions. We both used a class in order to have a strongly typed object to work with. He uses a dictionary collection, I'm using a list.

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