Organize products into arrays

Where does that list comes from?

In what format is the data?

Are you in Visual Basic or C#?

they are all inside a ConcurrentDictionary in vb.net

What is the data structure of the products that are in the dictionary?

the key ex: 598659659 then the name like "Shirt Blue Short Sleeves"

So your ConcurrentDictionary object is defined with a key of type integer and a value of type string something like this, ConcurrentDictionary<int, string>, is that correct?

Now the value having a type string with a value like this, "Shirt Blue Short Sleeves", so is the product type ALWAYS the first word in the string?

that's correct..
but if it makes things more simple I can make it Concurrent.ConcurrentDictionary(Of String, String())
and key=123456, value1=shirt, value2=brand and model

No need I just wanted to make sure where the product type was located in the Value string. Seeming that a List of objects is a type safe object would that be better for the collection of products? Seeming that you will be creating the collections at run time as per your statement, "put each product into an array. for example all shirts into one array and all shoes into an array", How will you be identifying each collection? Will you have predefined Array's/List to be filled? Or will you check the first entry and determine what type of list it is or something else.

i am okay with what makes things faster..