处理linq组的方法

Question

I have a simple list of integers (some values repeated) and process with:

var groups = from n in numbers
    group n by n into numGroup
    where numGroup.Count()>1
    select numGroup;

I can iterate over the groups with nested loops directly after the linq, but I am having trouble writing a separate method to loop through them. Here is what I have tried.

private void PrintGroups(IEnumerable groups, string title)
{
    int i = 0;
    foreach (var group in groups)
    {
        txt1.Text += "Group " + ++i + "\r\n"; ;
        foreach (var x in group)
               txt1.Text += "    " + x.ToString() + "\r\n"; ;
     }
}

The compiler doesn't like the inner foreach:

"foreach statement cannot operate on variables of type 'object' because 'object' does not contain a public definition for 'GetEnumerator'"

But the same code works inline with the linq. Any suggestions?

Answer 1

It looks to me like you just need to change the type of your parameter:

private void PrintGroups(IEnumerable<IGrouping<int, int>> groups, string title)

However, aren't you really just interested in the key and the count? After all, all the values in the group will be the same...

private void PrintGroups(IEnumerable<IGrouping<int, int>> groups)
{
    StringBuilder builder = new StringBuilder();
    foreach (var group in groups)
    {
        builder.AppendFormat("Group {0}: {1}\r\n", group.Key, group.Count());
    }
    txt1.Text = builder.ToString();
}

Answer 2

In Linq one thinks in projections, here is an example where I project the group of numbers into a string which can be displayed to the user.

 var nums = new List<int>() { 1, 1, 5, 6, 1, 5, 2 };

 nums.GroupBy (n => n)
     .Select (n => string.Format("Number {0} is found {1} times ({2})", n.Key, n.Count (), string.Join(",", n)))
     .ToList()
     .ForEach(strN => Console.WriteLine (strN));

/* Output

Number 1 is found 3 times (1,1,1)
Number 5 is found 2 times (5,5)
Number 6 is found 1 times (6)
Number 2 is found 1 times (2)

*/