Creating Collection dynamically in C#

Question

I have an application that will continuously taking user's input and store the input in a List of class ItemsValue

How am I going to make it so that once the collection reaches 1000 counts, it will "stop" and a new collection will be created and so on.

For example:

List<ItemsValue> collection1 = new List<ItemsValue>();
//User input will be stored in `collection1`
if (collection1.count >= 1000)
    //Create a new List<ItemsVales> collection2, 
    //and the user input will be stored in collection2 now.
    //And then if collection2.count reaches 1000, it will create collection3. 
    //collection3.count reaches 1000, create collection4 and so on.

You can make list of collections. But what's the original purpose? — Ulugbek Umirov, Apr 24 '14 at 15:54
[XY problem?](http://meta.stackexchange.com/questions/66377/what-is-the-xy-problem) — Liam, Apr 24 '14 at 15:55
@Liam definitely. This completely sounds like I have a solution to a problem, help me with my solution, not the problem. — Erik Philips, Apr 24 '14 at 15:56
possible duplicate of [How to loop through IEnumerable in batches](http://stackoverflow.com/questions/15414347/how-to-loop-through-ienumerable-in-batches) — Liam, Apr 24 '14 at 15:56
No, we need to temporary store the data in the list then transfer the data into the next application. — C.J., Apr 24 '14 at 15:57
If someone were to look at the question or at any of the answer without reading everything on this page first and use their intuition they would simply state: _Hey ! There's no way that the if statement will ever be true_ or .. _The index access operation [collections.Count - 1] will also throw an exception_. So please: don't be hasty, split the various pieces of code into their rightful places, explain the "event oriented" nature of the operations that are executed against the collection/collections. @Liam: this most surely is an XY problem (+1) — Eduard Dumitru, Apr 24 '14 at 16:04
@Liam It is not my intention to make this an XY problem. I have a job with a specific requirement, it is not up to me to question my clients about their decisions, even if their request sometimes make no sense, but I'm stuck with the Y. — C.J., Apr 24 '14 at 16:19

score 4 · Answer 1 · answered Apr 24 '14 at 15:56

4

I don't know why, but you want a "list of lists": List<List<ItemsValue>>.

List<List<ItemsValue>> collections = new List<List<ItemsValue>>();
collections.Add(new List<ItemsValue>());

collections.Last().Add(/*user input*/);

if (collections.Last().Count >= 1000) collections.Add(new List<ItemsValue>());

answered Apr 24 '14 at 15:56

Bobson

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1

Looks like we all answered at the same time! Yours seems most concise, so you get my vote. – Nick Udell Apr 24 '14 at 16:00
1

Yeah, but your code and @Selman22's code are the only ones which don't throw an exception. +1s – Eduard Dumitru Apr 24 '14 at 16:14

Selman Genç · Answer 2 · 2014-04-24T16:01:03.600

I think you need List<List<ItemsValue>>

List<List<ItemsValue>> mainCollection = new List<List<ItemsValue>>();
int counter = 0;
if (counter == 0) mainCollection.Add(new List<ItemsValue>());

if(mainCollection[counter].Count < 1000) mainCollection[counter].Add(item);

else 
{
    mainCollection.Add(new List<ItemsValue>());
    counter++;
    mainCollection[counter].Add(item);
}

I don't know how is the rest of your code look like,but I would make that counter static.

score 3 · Answer 3 · edited Jun 12 '14 at 08:42

3

Use a list of collections. If you have fixed size you can use a array instead of a list.

List<List<ItemsValue>> collections = new List<List<ItemsValue>>({new List<ItemsValue>()});
if(collections[collections.Count- 1].Count >= 1000)
{
   var newCollection = new List<ItemsValue>();
   // do what you want with newCollection
   collections.Add(newCollection);
}

edited Jun 12 '14 at 08:42

Nick Udell

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answered Apr 24 '14 at 15:57

Amir Popovich

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You can condense your if statement's body to collections.Add(new List()) without losing any real readability. – Nick Udell Apr 24 '14 at 15:59
It's not for readability, it's more for doing things with the new List. – Amir Popovich Apr 24 '14 at 16:00
Ah I see. Although you could easily get that new list by simply going collections.Last() later. – Nick Udell Apr 24 '14 at 16:01
1

Yup..nothing wrong with both approaches.. Cheers :) – Amir Popovich Apr 24 '14 at 16:02
1

Kudos for the compiler error in `collections[collections.Count - 1] >= 1000`, for the irrefutable `IndexOutOfBoundsException` should the code actually compile and for the upvoters' enthusiasm. This is nothing personal: The same goes for the question and the other N-1 answers. – Eduard Dumitru Apr 24 '14 at 16:10

Nick Udell · Answer 4 · 2014-04-27T15:07:55.963

2

Try this:

List<List<ItemsValue>> collections = new List<List<ItemsValue>>({new List<ItemsValue>()});

if(collections[collections.Count-1].Count >= 1000)
{
    collections.Add(new List<ItemsValue>());
}

Use the above if statement when you're adding an item to collections. To add an item to collections, use the following:

collections[collections.Count-1].Add(yourItem);

edited Apr 27 '14 at 15:07

answered Apr 24 '14 at 15:56

Nick Udell

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Creating Collection dynamically in C#

4 Answers4