如何迭代IGrouping <T>接口？

Question

Ive got ths really annoying issue I have grouped a set of data and I cant get to the data within the group. I can get to the key bit not the data..

I have a load of data that is in the form

Data.Period = x
Data.Adjustment = y

I perform a GroupBy

var groupedData = Data.GroupBy(x => x.Period new {x.Period});

This brings back (according to linq) my hierarchical data which is starting to look how I want it. Id like to iterate through the contents but cant...How do I do this? and how do I...

Work how to get to the Data.Adjustment without using a projection. And I dont want to project yet because I have to perform another grouping....help! :-)

Answer 1

The IGrouping<TKey, TElement> interface inherits IEnumerable<TElement> :

foreach (var group in groupedData)
{
    var groupKey = group.Key;
    foreach (var groupedItem in group)
        DoSomethingWith(groupKey, groupedItem);
}

I note that you will be better off using this for your query, however:

var groupedData = Data.GroupBy(x => x.Period); 

rather than this:

var groupedData = Data.GroupBy(x => new {x.Period}); 

If, for example, you wanted to average the adjustments, you could do this:

foreach (var group in groupedData)
    Console.WriteLine("Period: {0}; average adjustment: {1}", group.Key, group.Average(i => i.Adjustment));

Answer 2

Each element of a sequence of IGrouping<TKey, TElement> is an IEnumerable<TElement> that you can iterate over to get the data that has a common TKey :

var groups = Data.GroupBy(x => x.Period);
foreach(var group in groups) {
    Console.WriteLine("Period: {0}", group.Key);
    foreach(var item in group) {
        Console.WriteLine("Adjustment: {0}", item.Adjustment);
    }
}

So in the above, groups is an IEnumerable<IGrouping<TPeriod, TAdjustment>> where TPeriod is the type of Period (you didn't tell us) and TAdjustment is the type of Adjustment . Then, group is an object that implements IEnumerable<TAdjustment> (but it also has a Key property so that you can get the key. Finally, item is a TAdjustment , and for each group , all the item that come from iterating over that group have the same key.

Answer 3

Though maybe obvious for others one can also use:

var groups = Data.GroupBy(x => x.Period);

foreach(var group in groups)
{
   List<Data> dataListByPeriod = group.ToList();
   //use this list
}

Answer 4

Just use foreach :

foreach(var group in groupedData)
{
   Console.WriteLine("Period: {0}", group.Key);
   foreach(var item in group)
      Console.WriteLine("   Adjustment: {0}", item.Adjustment);
}

Answer 5

You can use following code as well.

var groupedData = Data.GroupBy(x => x.Period);

foreach (var group in groupedData) {
    var gr = group.FirstOrDefault();
    Console.WriteLine("Period: {0}", gr.Period);
    Console.WriteLine("Adjustment: {0}", gr.Adjustment);
}