Combination of two elements in array

Question

I had similar questions in the past - I have array with n elements in it, how can I get all combinations of two elements from it, without repeating?

Ie. if array is like this:

var arr1 = new[] { "A", "B", "C", "D", "E"};

... result should be

AB
AC
AD
AE
BC
BD
BE
CD
CE
CD

Can you help me please achieve this?

dup of http://stackoverflow.com/questions/1272828/getting-all-the-combinations-in-an-array — G-Man, Nov 22 '13 at 15:27
Possible answer here: http://stackoverflow.com/questions/4319049/generating-permutations-using-linq — sakura-bloom, Nov 22 '13 at 15:29

gpmurthy · Answer 1 · 2013-11-22T15:49:35.403

2

Consider the following Code...

var arr1 = new[] { "A", "B", "C", "D", "E" };
var combinations = new List<string>();
for(int i = 0; i < arr1.Length; i++)
{
    for (int j = i + 1; j < arr1.Length; j++)
    {
        combinations.Add(string.Format("{0}{1}", arr1[i], arr1[j]));
    }
}

Good Luck!

Added screenshot for reference...

enter image description here

edited Nov 22 '13 at 15:49

answered Nov 22 '13 at 15:35

gpmurthy

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This one's also goof although I think the answer from @jim tollan looks nicer because he doesn't need an extra if statement. :) – Abbas Nov 22 '13 at 15:50

sjkm · Answer 2 · 2013-11-22T15:46:14.967

1

var arr1 = new[] { "A", "B", "C", "D", "E" };
var combinations = new List<string>();
foreach (var i in arr1) {
    foreach (var j in arr1) {
         if((int)i.ToCharArray()[0] < (int)j.ToCharArray()[0]) {
             combinations.Add(i + j);
         }
    }
}

now the combinations list contains all combinations!

edited Nov 22 '13 at 15:46

answered Nov 22 '13 at 15:26

sjkm

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I upvoted it but later understood that it is incorrect. It will produce both AB and BA which is not wanted. – Andrey Nov 22 '13 at 15:35
@sjkm: But it's still the wrong result (20 instead of 10). – Tim Schmelter Nov 22 '13 at 15:43
You allow `AB` to be in the result as well as `BA`, while only `AB` is expected! – Abbas Nov 22 '13 at 15:46
Ah I see, but now it should be right – sjkm Nov 22 '13 at 15:46

score 1 · Answer 3 · answered Nov 22 '13 at 15:36

1

ok, my feeble attempt:

var myArray = new[] { "A", "B", "C", "D", "E" };
var myCombos = new List<string>();
for (int i = 0; i < myArray.Length; i++)
{
    for (int j = (i + 1); j < myArray.Length; j++)
    {
        myCombos.Add(myArray[i] + myArray[j]);
    }
}

now we have:

AB AC AD AE BC BD BE CD CE DE

answered Nov 22 '13 at 15:36

jim tollan

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Seems the only correct attempt so far.. :) – Abbas Nov 22 '13 at 15:46
1

yeah, and i certainly aint no genius - lol. had to think back to the old basic posers from way back. nice brain teaser tho – jim tollan Nov 22 '13 at 15:48
No, you haven't got downvotes. I can see up/down votes apart per answer and it only says 1up/0down => +1. – Abbas Nov 22 '13 at 15:57
paranoid -who's paranoid :-)?!?. must be my friday madness going on. btw, enjoyed your curating of the answers, makes it feel quite *live*. nice one - have a grt weekend Abbas – jim tollan Nov 22 '13 at 16:01

Tilak · Answer 4 · 2013-11-22T15:48:47.263

0

Try following (cross join in LINQ)

  var arr1 = new[] { "A", "B", "C", "D", "E"};
  var result = (from i1 in arr1
             from i2 in arr1.Where( i=> i[0]>i1[0])
            select i1+i2).ToArray();

Snippet result on ideone here

AB
AC
AD
AE
BC
BD
BE
CD
CE
DE

edited Nov 22 '13 at 15:48

answered Nov 22 '13 at 15:26

Tilak

30,108
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2

You should filter same el pairs, like "AA" – Andrey Nov 22 '13 at 15:26
too fast and too inexact :) – King King Nov 22 '13 at 15:27
And filter out BA etc. – Jon Skeet Nov 22 '13 at 15:28

Tim Schmelter · Answer 5 · 2013-11-22T15:46:37.073

0

Maybe this little LINQ query:

var allCombinations = from str1 in arr1
                      from str2 in arr1
                      where str1.CompareTo(str2) < 0
                      select str1 + str2;
Console.Write(string.Join(",", allCombinations));

My last is different, i assume that was a typo in your result: AB,AC,AD,AE,BC,BD,BE,CD,CE,DE

edited Nov 22 '13 at 15:46

answered Nov 22 '13 at 15:34

Tim Schmelter

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Why don't you run it first? It clearly produces different result than the one asked in the question. – Andrey Nov 22 '13 at 15:36

Combination of two elements in array

5 Answers5