How can I get the the value of an element of a list?

Question

2.00/5 (3 votes)

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C#

//How to get the price of a certain product from the list? Example the Ipad. How can I get the price and return the value in a label.


//My Class

public class ProductInfo

    {
       string _name;
       string _location;
       double _price;

    public ProductInfo(string name, string location, double price)
    {
       _name = name;
       _location = location;
       _price = price;
    }


 public string Name{ get; set}

 public string Location{ get; set}

 public double Price{ get; set}

}
}
//This is my List
    List<ProductInfo> Product = new List< ProductInfo >();

            Product.Add(new ProductInfo ("Ipad", "USA", 585.56));
            Product.Add(new ProductInfo ("Laptop", "USA", 1227.75));
            Product.Add(new ProductInfo ("MemoryCard", "USA", 32.77));
            Product.Add(new ProductInfo ("Mouse", "USA", 56.19));
            Product.Add(new ProductInfo ("HardDisk", "USA", 165.50));
            Product.Add(new ProductInfo ("Monitor", "USA", 286.90,));

Posted 24-Mar-12 13:58pm

Member 8714846

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Comments

Clifford Nelson 25-Mar-12 20:30pm

I voted 4 since this gave an opportunity to have many people respond.

5 solutions

Solution 4

Here is a cleaner solution:

C#

var price = Products.FirstOrDefault(i => i.Name = productName).Select(i => i.price);

In good design, there should not be a case where you get a null back, and if you do, it should probably be an exception. This is probably an exception because there is a bug somewhere in the code. An exception can be caught with the above code with a try catch block. But if you want a default then use Linq properly:

C#

var price = Products.FirstOrDefault(i => i.Name = productName).Select(i => i i == null ? 0 : i.price);

Posted 24-Mar-12 17:26pm

Clifford Nelson

Updated 25-Mar-12 14:24pm

v3

Comments

ProEnggSoft 25-Mar-12 0:56am

It's good. +5 for the idea.
I have some comments please my see solution (5)

ProEnggSoft 25-Mar-12 20:26pm

I have seen the modification done in my answer. But, please indicate what you have modified, if you have edited others answer.
Further, I have up voted your answer. Whereas it seems you have down voted my answers. Thank you.

Clifford Nelson 25-Mar-12 20:29pm

I have an issue with you response as stated above. I would hope that the design would not lookup a price when there is no such produce. This is an exception.

ProEnggSoft 25-Mar-12 20:41pm

Please see my comment to your response above. Thank you.

Clifford Nelson 25-Mar-12 21:12pm

As noted in my response to your responce.

Solution 2

The solution 1 given by Shahin Khorshidnia is correct, only thing is he has used the method syntax of LINQ. The Query syntax of LINQ is easy to read, as given below

C#

List<ProductInfo> Products = new List< ProductInfo >() {
            new ProductInfo ("Ipad", "USA", 585.56),
            new ProductInfo ("Laptop", "USA", 1227.75),
            new ProductInfo ("MemoryCard", "USA", 32.77),
            new ProductInfo ("Mouse", "USA", 56.19),
            new ProductInfo ("HardDisk", "USA", 165.50),
            new ProductInfo ("Monitor", "USA", 286.90)};

//I have used StringComparison.InvariantCultureIgnoreCase to safeguard against the comparison of characters 
//English characters when other culture is current culture. 
//However other options can be used as per your requirement
var selectedProductPrices = from product in Products
                        where product.Name.Equals("Ipad", StringComparison.InvariantCultureIgnoreCase)
                        select product.Price;
double selectedProductPrice =  selectedProductPrices.Count() > 0 ? selectedProductPrices.First() : 0;

As he pointed out when Auto Implemented properties are used there is no need of back end store.
Further, I suggest to use plural for List objects i.e. instead of Product say Products, this gives more clarity while working with the code.

Posted 24-Mar-12 16:20pm

ProEnggSoft

Updated 24-Mar-12 16:27pm

v2

Comments

Shahin Khorshidnia 25-Mar-12 5:32am

Thanks. My +5

ProEnggSoft 25-Mar-12 5:37am

Thank you.

Solution 3

At the simplest, you can run a loop and retrieve the item you are looking for.
For r.g.

C#

foreach (ProductInfo o in Product)
{
    if (o.Name == "Ipad")
    {
       MessageBox.Show(o.Price.ToString());
    }
}

Posted 24-Mar-12 16:21pm

Abhinav S

Comments

Shahin Khorshidnia 25-Mar-12 5:43am

foreach has a better performance than LINQ, I tested it;) but Linq is more clear, shorter and if it be used correctly and timly, somethimes it is able to have a better performance.

My +4 to your solution
Of course in this way, it needs a break too.
foreach (ProductInfo o in Product)
{
if (o.Name == "Ipad")
{
MessageBox.Show(o.Price.ToString());
break;
}
}

Abhinav S 25-Mar-12 22:14pm

Fair point about the break statement. Thanks.

Shahin Khorshidnia 25-Mar-12 22:22pm

You're welcome ;)

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ProEnggSoft · Accepted Answer · 2012-03-24T19:10:00

Solution 5

The FirstOrDefault extension method of IEnumerable interface returns the first occurance or the default value of the collection member.

C#

var price = Products.FirstOrDefault(i => i.Name = productName).Select(i => i.price);

In this case it returns the ProductInfo object.
The ProductInfo class does not have Select method Hence, the .Select will throw error in the above statement.
So, instead of .Select(i => i.price) we have to use .Price.
ProductName is a string, = in i.Name = productName is to be == for comparison

But, when the List is empty the FirstOrDefault returns null as the default value for a reference type is null and if the required product is not found say we passed Ipad2, the method returns null. In either case if we directly access Price property on the object returned by the FindOrDefault method, there is a chance of error. Hence, I think the better option would be

C#

ProductInfo selectedProductInfo = Products.FirstOrDefault(p => p.Name == productName);
double price = selectedProductInfo == null ? 0 : selectedProductInfo.Price;

[EDIT]The following text inserted by Clifford Nelson[EDIT]
May not have an issue with null, and can cover with an exception. During debug can put an Debug.Asser. Can also do the following

var price = (Products.FirstOrDefault(i => i.Name = productName) ?? new Preduct()).Select(i => i.price);

Posted 24-Mar-12 19:10pm

ProEnggSoft

Updated 25-Mar-12 14:22pm

v4

Comments

Shahin Khorshidnia 25-Mar-12 5:52am

Good answer

ProEnggSoft 25-Mar-12 6:25am

Thank you

Member 8714846 25-Mar-12 11:46am

Awesome..

ProEnggSoft 25-Mar-12 12:00pm

Thank you.

Clifford Nelson 25-Mar-12 20:27pm

Why not just include the second line in the LINQ statement??? Plus, if you do not find the value, that might be an exception. When should be get far enough to be looking up a price when you have the name. Sound like a serious design problem and an exception should be raised anyway. Plus you can continue in LINQ, why not continue in LINQ! Otherwise why even bother with LINQ in the first place. I have further improved the answer after some thought.

ProEnggSoft 25-Mar-12 20:39pm

What you have given is another alternative. In programming several possibilities are there. If we write a statement in a short way does not mean that the other way is wrong and justify for a down vote. Regarding, the product not found, the designer can raise an exception. It is also a preferred approach, when we surely know that what is the output of a statement, we can deal with it without throwing an exception, as throwing an exception is an overhead in program. I have read that the TryParse method of Int, Double etc. was introduced to deal with failure of conversion without using try catch block. Thank you

Clifford Nelson 25-Mar-12 20:53pm

As stated the lambda will throw an exception, but I look at it and ask when should you ever get that far in the solution, and have a bad name. And if you have a bad name, should you return 0, or throw and exception. I say there is a serious desing problem if you get this far, and saying that a value of 0 should be returned is an assumption. Yes that might be the right answer sometimes, but ussually it should be an exception. If you had discussed this, I would have commended you, but you. You ignored the design issue and assumed that 0 was the right answer. No that is an assumption. I would think that you would want to know that there was nother found. If you return a value in an exception condition, you are putting in bugs that are going to be really hard to find. Give the exception, and have the designer fix the real issue, and don't put the application in the situation where a subtle problem will occur that may never be found, and can cause some really serious liability issues.

ProEnggSoft 25-Mar-12 21:01pm

Thank you for your reply.
I have clearly stated in my answer when the null will be returned. So the designer already kept informed that there is a possibility of null. Further the second statement in my answer is only for completeness and does not require the user to only return 0. He can choose any other option, since it is already clearly stated that null will be returned.
If we go by your version, then the user should not look up in an empty list as it is a design problem, then Find method is more appropriate, but you have given FirstOrDefault method.

Clifford Nelson 25-Mar-12 21:11pm

Returning a null means that that means have to deal with the null further up the line, which adds complexity, and that increases the maintenance. This is a perfect case of where you want to use and exception. Yes exceptions have a performance cost, but when you are truely in an exception case (should not be passing in a bad name), this should not be normal condition, so it really has no cost. Want to find these bugs, which it is, and squash them.

ProEnggSoft 25-Mar-12 21:15pm

I think this discussion is going too far. Let us close. Thank you very much for the debate.

Shahin Khorshidnia · Accepted Answer · 2012-03-24T14:45:00

Hello

First thing.

Your class must defined like this:

C#

public class ProductInfo
{
    //string _name;
    //string _location;
    //double _price;

    public ProductInfo(string name, string location, double price)
    {
        Name = name;
        Location = location;
        Price = price;
    }


    public string Name { get; set; }

    public string Location { get; set; }

    public double Price { get; set; }
}

If you realy want full properties, then:

C#

public class ProductInfo
{
    public ProductInfo(string name, string location, double price)
    {
        Name = name;
        Location = location;
        Price = price;
    }

    private string _name;
    public string Name
    {
        get { return _name; }
        set { _name = value; }
    }

    private string _location;
    public string Location
    {
        get { return _location; }
        set { _location = value; }
    }

    private double _price;
    public double Price
    {
        get { return _price; }
        set { _price = value; }
    }
}

Then for getting the price:

C#

var prices = Product.Where(p => p.Name == "Mouse").Select(p => p.Price);
double price;
if (prices.Count() > 0)
    price = prices.First();

How can I get the the value of an element of a list?

5 solutions

Solution 4

Solution 5

Solution 1

Solution 2

Solution 3

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