Foreach IEnumerable reference by string

Question

I am trying to access the contents of an IEnumerable by string rather than int.

METHOD

public List<Foo> GetFoo(IEnumerable<Bar> bar)
{
    List<Foo> foo = new List<Foo>();

    var query = from x in bar       
                select new Foo()
                {
                    foo = x.foo,
                    bar = x.bar
                };
    foo = query.ToList();
    return foo;
}

VIEW

<td>@foo["bar"].foo<td>

I know the above doesn't exist, but that's what i'm looking to do. If i do foo[0].foo it --obviously-- works.

EDIT

I went with the Dictionary<string,Foo> approach as @D Stanley and @juharr recommended, but i still have to iterate through these results via a foreach loop in order to access the KeyValuePair. I'm trying to bypass a foreach and access the results just via the Key. Is this possible?

public Dictionary<string,Foo> GetFoo(IEnumerable<Bar> bar)
{
    var query = from x in bar               
                select new Foo()
                {
                    foo = x.foo,
                    bar = x.bar
                };
    return query.ToDictionary(f=>f.foo,f=>f);            
}

How are you expecting this to work? Which element of the sequence should `foo["bar"]` return? — Lee, Jun 14 '16 at 18:30
i'm currently running a foreach within a foreach and saying `if item.foo==item2.foo then ....`. I was trying to bypass this logic by just running 1 foreach and accessing the other IEnumerable by the item.foo. that make sense? — jellz77, Jun 14 '16 at 18:31
@Rahul can i store multiple values in a dictionary or just Key->Value? I come from a PHP background so i'm really looking for a multi-dimensional array — jellz77, Jun 14 '16 at 18:35
@jellz77 you can store multiple Key-Value pairs, but the key has to be unique and not null. — juharr, Jun 14 '16 at 18:36
@jellz77 How would `foo["bar"].foo` work if there were multiple objects mapped to `"bar"`? It would be a lot more clear if you wouldn't reuse the type names for variables and properties. — D Stanley, Jun 14 '16 at 18:40

D Stanley · Accepted Answer · 2016-06-14T19:13:18.927

1

There's nothing that compact with the List structure. It only has an indexer that accepts integers (the index of the item you want). A few options:

Subtype List<Foo> to add an indexer that accepts a string

Use a dictionary instead of a List<Foo>:

public Dictionary<string,Foo> GetFoo(IEnumerable<Bar> bar)
{
    var query = from x in bar       
                select new Foo()
                {
                    x.foo,
                    x.bar
                };

    return query.ToDictionary(f => f.bar, f => f));
}

then foo["bar"] will give the the Foo object indexed by "bar". You do not need to iterate the entire collection to find the object with the matching key.

edited Jun 14 '16 at 19:13

answered Jun 14 '16 at 18:38

D Stanley

149,601
11
178
240

this did it! thanks! – jellz77 Jun 14 '16 at 18:42
the results are still being stored as ints, then the KeyValuePair? – jellz77 Jun 14 '16 at 18:53
in your example, i'd still have to iterate through the results in a foreach then access the key once in the foreach – jellz77 Jun 14 '16 at 18:54
I'm not sure what you man by either comment - a dictionary is designed for fast access by key - yes you still need to loop through if you want to iterate the keys. Your example indicated that you wanted _a specific key_, though. – D Stanley Jun 14 '16 at 18:57
correct so ideally i want to access foo["randomString1"].someValue without the implementation of a foreach. The reason i don't want to run a foreach is because i already have multiple foreach statements in my view and am looking for fast access to a KeyValue. – jellz77 Jun 14 '16 at 19:01
What I gave you gives you fast access by key value. I don't see where you're using `foreach` so I don't know what the problem is. But if you think you need to iterate the entire collection to find the matching key then see my update. – D Stanley Jun 14 '16 at 19:11

score 0 · Answer 2 · edited May 23 '17 at 12:00

With a little more digging, i was able to find the answer through C# List of objects, how do I get the sum of a property

Using my example above, i implemented the following logic using linq:

METHOD

public List<Foo> GetFoo(IEnumerable<Bar> bar)
{
    List<Foo> foo = new List<Foo>();

    var query = from x in bar       
                select new Foo()
                {
                    name= x.name,
                    amount = x.amount
                };
    foo = query.ToList();
    return foo;
}

VIEW

@double total = foo.Where(item => item.name == "jon").Sum(item => item.amount);    
<td>@total<td>

within my view, i'd replace "jon" with a variable to alleviate a foreach within a foreach. sorry for the confusion all, but appreciate everyone's help!!

Foreach IEnumerable reference by string

2 Answers2