Get grouped comma separated values with linq

问题:

I would like a third column "items" with the values that are grouped.

var dic = new Dictionary<string, int>();
dic.Add("a", 1);
dic.Add("b", 1);
dic.Add("c", 2);
dic.Add("d", 3);

var dCounts =
    (from i in dic
    group i by i.Value into g
    select new { g.Key, count = g.Count()});

    var a = dCounts.Where(c => c.count>1 );

dCounts.Dump();
a.Dump();

This code results in:

Key Count
1   2
2   1
3   1

I would like these results:

Key Count Items
1   2     a, b
2   1     c
3   1     d

回答1:

    var dCounts =
        (from i in dic
            group i by i.Value into g
            select new { g.Key, count = g.Count(), Items = string.Join(",", g.Select(kvp => kvp.Key)) });

Use string.Join(",", {array}), passing in your array of keys.

回答2:

You can use:

var dCounts = 
    from i in dic 
    group i by i.Value into g 
    select new { g.Key, Count = g.Count(), Values = g }; 

The result created by grouping (value g) has a property Key that gives you the key, but it also implements IEnumerable<T> that allows you to access individual values in the group. If you return just g then you can iterate over all values using foreach or process them using LINQ.

Here is a simple dump function to demonstrate this:

foreach(var el in dCounts) {
  Console.Write(" - {0}, count: {1}, values:", el.Key, el.Count);
  foreach(var item in el.Values) Console.Write("{0}, ", item);
|

回答3:

from i in dic 
group i.Key by i.Value into g 
select new
{
  g.Key,
  count = g.Count(),
  items = string.Join(",", g.ToArray())
});