Create list in C#

Question

I am trying to create a class like this:

public class person
{
    public string name { get; set;}
    public int age  { get; set;}
}

and create a class which is basically a list of the class above:

public class PersonList : List<person>
{
    public PersonList()
    { 
    }

    public int getAge(string name)
    { 
        foreach( string s n this)
        {
            if ( s == name)
                return age;
        }
    }

My goal is to have simple function named GetAge() so I get the the age by name of any person object in my list. I know it is possible to just create a list, but I want a modular code.

And what problem do you have ? The code seems ok, should work — Titian Cernicova-Dragomir, Sep 13 '17 at 15:49
Your loop in the getAge can't be iterated as string. The type in the list isn't a string, its person. — Jay, Sep 13 '17 at 15:52
There are easier/more elegant ways to get the property of a list item using linq — Ňɏssa Pøngjǣrdenlarp, Sep 13 '17 at 15:52
What you're apparently trying to do is `return this.FirstOrDefault(a=> a.name == name)?.age ?? 0;` — Felype, Sep 13 '17 at 15:53
@Felype 0 is not an ideal return type in case of null as a baby will have age 0. A negative number is better. — Yair Halberstadt, Sep 13 '17 at 15:59
Yes, indeed. I did not consider. Alternatively the return value could be a nullable int, or that function could throw an exception when name is not found. — Felype, Sep 13 '17 at 16:01
[Don't inherit from `List`!](https://stackoverflow.com/questions/21692193/why-not-inherit-from-listt) — Scott, Sep 13 '17 at 16:07
@Scott. Your link doesn't say never inherit from list, it says only inherit from list if the inherited object actually is a list, which it is in this case. — Yair Halberstadt, Sep 13 '17 at 16:14

Yair Halberstadt · Answer 1 · 2017-09-13T15:58:12.443

2

public int getAge(string name)
{ 
     return this.First(x=>x.name==name).age;       
}

This will throw an error if person not found.

To return -1 when person is not found:

public int getAge(string name)
{ 
     return this.FirstOrDefault(x=>x.name==name)?.age??-1;       
}

edited Sep 13 '17 at 15:58

answered Sep 13 '17 at 15:53

Yair Halberstadt

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score 0 · Answer 2 · answered Sep 13 '17 at 16:26

I think you must consider that a name can be repeated in a list so you arbitrarily would be getting the first one, in the sample below you have two options.

public class person
    {
        public string name { get; set; }
        public int age { get; set; }
    }
    public class PersonList : List<person>
    {
        public int getAge(string name)
        {
            return this.FirstOrDefault(x => x.name == name)?.age ?? -1;
        }
        public int[] getAge2(string name)
        {
            return this.Where(x => x.name == name).Select(x=>x.age).ToArray();
        }
    }

And you will get a list of ages in case the name is repeated, console code below

static void Main(string[] args)
        {
            PersonList listOfPerson = new PersonList();
            listOfPerson.Add(new person() { age = 25, name = "jhon" });
            listOfPerson.Add(new person() { age = 26, name = "jhon" });
            listOfPerson.Add(new person() { age = 21, name = "homer" });
            listOfPerson.Add(new person() { age = 22, name = "bill" });
            listOfPerson.Add(new person() { age = 27, name = "jhon" });
            listOfPerson.Add(new person() { age = 22, name = "andrew" });

            foreach (var item in listOfPerson.getAge2("jhond"))
            {
                Console.WriteLine(item);
            }
            Console.ReadLine();
        }

Create list in C#

2 Answers2