How can I traverse this list in this manner?

Question

I have a list of objects that looks like this :

ID:2000
Title:"Title 1"
Description:"My name is Marco"

ID:2000
Title:"Title 2"
Description:"My name is Luca"

ID:3000
Title:"Title 3"
Description:"My name is Paul"

ID:4000
Title:"Title 4"
Description:"My name is Anthony"

ID:4000
Title:"Title 5"
Description:"My name is Carl"

ID:4000
Title:"Title 6"
Description:"My name is Jadett"

now, I'd like to browse (traverse) it with a for each. But I want to traverse it starting from the same ID. So, first a foreach for the single/unique ID (2000, 3000, 4000, so 3 steps). Than, for each "ID" step, each Title/Description: so 2 steps for the ID 2000, 1 for the ID 3000 and 3 for the ID 4000. List is ordered by ID.

How can I do it? Group by? Uhm...

Answer 1

Yes, with a group by:

foreach (var group in items.GroupBy(i => i.ID))
{
    foreach (var item in group)
    {
    } 
}

Answer 2

Yes, you can use GroupBy.

first the groups itself:

var idGroups = items.GroupBy(i => i.ID).ToList(); // omit ToList() if scalability is more important than performance since it creates a new list but doesn't enables to enumerate the result multiple times without querying again
foreach(var idGroup in idGroups)
{
    // ...
}

then all items of each group:

foreach (var idGroup in idGroups)
{
    foreach (var item in idGroup)
    {
        // ...
    } 
}