Intersection for Two List problem

Sin Yee

Hi...i am trying doing the intersection between two List. but, i tried many times still cannot get it. Hope someone can help me...

Here is the coding.
List> L = new List>(sItem.ToList());
L.Reverse();
L.Sort(delegate(KeyValuePair lhs, KeyValuePair rhs)
{ return rhs.Value.CompareTo(lhs.Value); });

foreach (KeyValuePair val in L)
{
show3 += val.Key+"\r\n";
}
MessageBox.Show(show3.ToString());

List> P = new List>(itemS.ToList());
foreach (KeyValuePair pair in P)
{
show4 += pair.Key+"\r\n";
}
MessageBox.Show(show4.ToString());

12 Replies

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Vulpes15y ago
Accepted answer
Well, I'm even more confused now than I was before!

To put things in a Dictionary (or a Hashtable) you have to have a key and a value and I still don't know which is which as I don't see any strings here :(

Anyway, let's suppose that you (somehow) have two Dictionaries and you're trying to produce a third Dictionary which contains those key/value pairs which are common to the other two Dictionaries. Then you could go about it like this (untested code):

var dict1 = new Dictionary();
// code to fill dict1

var dict2 = new Dictionary();
// code to fill dict2

var dict3 = new Dictionary();

foreach(string key in dict1.Keys)
{
   if(dict2.ContainsKey(key) && dict1[key] == dict2[key])
   {
   dict3.Add(key, dict1[key]);
   }
}
Sin Yee15y ago
Now i put first group of number in dictionary and the second group of number in dictionary
Sin Yee15y ago
My key is string and value is int. the first group of number (single value) is in dictionary and the second group of number(many lines of number) is in hashtable..
Vulpes15y ago
Before I (or anyone else) can produce some code for this, we need to know what is the key (a string) and what is the value (an int) in your two lists.

Also, is it acceptable to produce an intersection of digits as I've illustrated above?
Sin Yee15y ago
So, if i want to use these two group of number to do intersection, what should i do...?
Vulpes15y ago
Well, I don't know what that's supposed to be but it's certainly not an intersection of the digits used in corresponding elements of the two lists.

The intersection would be:

2
(empty)
(empty)
4

The union would be:

2 1 2
1 2 3 4
3 2 5
4 3 4

and the union without duplicates would be:

2 1
1 2 3 4
3 2 5
4 3

Also I still don't see any sign of KeyValuePairs here??
Sin Yee15y ago
i want use the list one to intersect list two to get the data like this
eg.
2 1
2 3 4
2 5
3 4
like this....
Vulpes15y ago
No, the two lists are mutually exclusive.

The elements of the first list are all single digits.

The elements of the second list are either two or three digits.

Also I don't see any evidence of KeyValuePairs?

What output are you expecting to get?
Sin Yee15y ago
i got try my two LISTs. One list output is like this
2
1
3
4
5
the List 2 output is like this
1 2
2 3 4
2 5
3 4 .... so, are these two List can intersect together..???
Vulpes15y ago
Well, the code does work because I tested it before posting.

If there's no output, then the two lists can't have any KeyValuePairs in common.

Check what happens if you use the Union rather than the Intersect method.
Sin Yee15y ago
i had tried ur code..but no output appear in messagebox.....
Vulpes15y ago
You can use this code to get the intersection between your two lists, L and P, using LINQ. Only key/value pairs which match exactly will, of course, be included in the intersection:

   List> I = (L.Intersect(P)).ToList();
   string show5 = "";

   foreach (KeyValuePair pair in I)
   {
   show5 += pair.Key+"\r\n";
   }
   MessageBox.Show(show5.ToString());