Styjun

I want to group a list of key value pairs by key, then to group all the keys which have the same list of value.

Here is an exemple

| Key | Value |
|:----|------:|
| 1 | A |
| 1 | B |
| 1 | C |
| 2 | A |
| 2 | B |
| 3 | A |

Here is the result I would like to have

| Keys | Values |
|:-----|-------:|
| 1,2 | A,B |
| 1 | C |
| 3 | A |

I started with a classic GroupBy, but I am stuck in the second step to group the keys

var pairs = new List<KeyValuePair<string, string>>

 new KeyValuePair<string, string>("1", "A"),
 new KeyValuePair<string, string>("1", "B"),
 new KeyValuePair<string, string>("1", "C"),
 new KeyValuePair<string, string>("2", "A"),
 new KeyValuePair<string, string>("2", "B"),
 new KeyValuePair<string, string>("3", "A")
;
var groupingFirstStep = pairs.GroupBy(p => p.Key);

| Key | Values |
|:-----|-------:|
| 1 | A,B,C |
| 2 | A,B |
| 3 | A |

Other examples: on the left the input, on the right the expected result

| Key | Value | | Keys | Values |
|:----|------:| |:-----|-------:|
| 1 | A | | 1,2 | A,B |
| 1 | B |
| 2 | A |
| 2 | B |

| Key | Value | | Keys | Values |
|:----|------:| |:-----|-------:|
| 1 | A | | 1,2 | A,B |
| 1 | B | | 1 | C |
| 1 | C |
| 2 | A |
| 2 | B |

| Key | Value | | Keys | Values |
|:----|------:| |:-----|-------:|
| 1 | A | | 1,2 | A,B |
| 1 | B | | 1,3 | C |
| 1 | C | | 3 | A |
| 2 | A |
| 2 | B | Other possibility
| 3 | A | | 1,3 | A,C |
| 3 | C | | 1,2 | B |
 | 2 | A |

I think this is what you need. I omitted KeyValuePair with C, because I assumed that you would like to know how to group keys when the value (in this case A,B) is the same:

var pairs = new List<KeyValuePair<string, string>>

 new KeyValuePair<string, string>("1", "A"),
 new KeyValuePair<string, string>("1", "B"),
 new KeyValuePair<string, string>("2", "A"),
 new KeyValuePair<string, string>("2", "B"),
 new KeyValuePair<string, string>("3", "A")
;
var grouping = pairs.GroupBy(p => p.Key)
 .GroupBy(g => string.Join(",", g.Select(kvp => kvp.Value)));

You can use this overload of .GroupBy to project the values out of it.

Something like this:

static void Main(string[] args)

 var pairs = new List<KeyValuePair<string, string>>
 
 new KeyValuePair<string, string>("1", "A"),
 new KeyValuePair<string, string>("1", "B"),
 new KeyValuePair<string, string>("1", "C"),
 new KeyValuePair<string, string>("2", "A"),
 new KeyValuePair<string, string>("2", "B"),
 new KeyValuePair<string, string>("3", "A")
 ;

 IEnumerable<string> groupings = pairs.GroupBy(x => x.Key, x => x.Value, (x, y) => $"xt 

Outputting:

1 | A,B,C
2 | A,B
3 | A