I need to be able to make a list that contains all possible combinations of an inputted list.
For example the list `[1,2,3]` should return `[1 [1,2] [1,3] 2 [2,3] 3 [1,2,3]]`
The list doesn&#39;t have to be in any particular order. On this site I&#39;ve found lots of functions using the `itertools` but those are returning objects when I need just a `list`.


Making all possible combinations of a list

I have a list of integers `List&lt;int&gt;` in my C# program. However, I know the number of items I have in my list only at runtime.

Let us say, for the sake of simplicity, my list is `{1, 2, 3}`
Now I need to generate *all possible combinations* as follows.

    {1, 2, 3}
    {1, 2}
    {1, 3}
    {2, 3}
    {1}
    {2}
    {3}

Can somebody please help with this?

All Possible Combinations of a list of Values

I&#39;im trying to find all combinations of items in several arrays.
The number of arrays is random (this can be 2, 3, 4, 5...).
The number of elements in each array is random too...

For exemple, I have the 3 arrays :

    $arrayA = array(&#39;A1&#39;,&#39;A2&#39;,&#39;A3&#39;);
    $arrayB = array(&#39;B1&#39;,&#39;B2&#39;,&#39;B3&#39;);
    $arrayC = array(&#39;C1&#39;,&#39;C2&#39;);

I would like to generate an array with 3 x 3 x 2 = 18 combinations :

- A1, B1, C1
- A1, B1, C2
- A1, B2, C1
- A1, B2, C2
- A1, B3, C1
- A1, B3, C2
- A2, B1, C1
- A2, B1, C2
...

The problem is to create a function with a variable number of source arrays...



How to generate in PHP all combinations of items in multiple arrays

This question pops up quite often in one form or another (see for example [here][1] or [here][2]). So I thought I&#39;d present it in a general form, and provide an answer which might serve for future reference.

&gt; Given an arbitrary number `n` of vectors of possibly different sizes, generate an `n`-column matrix whose rows describe all combinations of elements taken from those vectors (Cartesian product) .

For example,

    vectors = { [1 2], [3 6 9], [10 20] }

should give

    combs = [ 1     3    10
              1     3    20
              1     6    10
              1     6    20
              1     9    10
              1     9    20
              2     3    10
              2     3    20
              2     6    10
              2     6    20
              2     9    10
              2     9    20 ]


  [1]: https://stackoverflow.com/q/21804025/2586922
  [2]: https://stackoverflow.com/q/21867681/2586922

Generate a matrix containing all combinations of elements taken from n vectors

I&#39;ve seen several similar questions about how to generate all possible combinations of elements in an array. But I&#39;m having a very hard time figuring out how to write an algorithm that will only output combination **pairs**. Any suggestions would be super appreciated!

Starting with the following array (with N elements): 

    var array = [&quot;apple&quot;, &quot;banana&quot;, &quot;lemon&quot;, &quot;mango&quot;];

And getting the following result:

    var result = [
       &quot;apple banana&quot;
       &quot;apple lemon&quot;
       &quot;apple mango&quot;
       &quot;banana lemon&quot;
       &quot;banana mango&quot;
       &quot;lemon mango&quot;
    ];


I was trying out the following approach but this results in all possible combinations, instead only combination pairs.

    var letters = splSentences;
    var combi = [];
    var temp= &quot;&quot;;
    var letLen = Math.pow(2, letters.length);
    
    for (var i = 0; i &lt; letLen ; i++){
        temp= &quot;&quot;;
        for (var j=0;j&lt;letters.length;j++) {
            if ((i &amp; Math.pow(2,j))){ 
                temp += letters[j]+ &quot; &quot;
            }
        }
        if (temp !== &quot;&quot;) {
            combi.push(temp);
        }
    }

Javascript - Generating all combinations of elements in a single array (in pairs)

How would you go about testing all possible combinations of additions from a given set `N` of numbers so they add up to a given final number?

A brief example:

 - Set of numbers to add: `N = {1,5,22,15,0,...}`
 - Desired result: `12345`

Finding all possible combinations of numbers to reach a given sum

I don&#39;t actually know how to describe what I wanted, but I&#39;ll show you:

For example:

    $data1 = &quot;the color is&quot;;
    $data2 = &quot;red&quot;;

What should I do (or process) so $result is the combination of `$data1` and `$data2`?

Desired result:

    $result = &quot;the color is red&quot;;




How can I combine two strings together in PHP?

I need to compute combinatorials (nCr) in Python but cannot find the function to do that in `math`, `numpy` or `stat`  libraries. Something like a function of the type:

    comb = calculate_combinations(n, r)

I need the number of possible combinations, not the actual combinations, so `itertools.combinations` does not interest me.

Finally, I want to avoid using factorials, as the numbers I&#39;ll be calculating the combinations for can get too big and the factorials are going to be monstrous.

This seems like a REALLY easy to answer question, however I am being drowned in questions about generating all the actual combinations, which is not what I want.


Statistics: combinations in Python

I want to write a function that takes an array of letters as an argument and a number of those letters to select. 

Say you provide an array of 8 letters and want to select 3 letters from that. Then you should get:

    8! / ((8 - 3)! * 3!) = 56

Arrays (or words) in return consisting of 3 letters each.



Algorithm to return all combinations of k elements from n

I have a list with 15 numbers in, and I need to write some code that produces all 32,768 combinations of those numbers. 

I&#39;ve found [some code][1] (by Googling) that apparently does what I&#39;m looking for, but I found the code fairly opaque and am wary of using it. Plus I have a feeling there must be a more elegant solution.

The only thing that occurs to me would be to just loop through the decimal integers 1–32768 and convert those to binary, and use the binary representation as a filter to pick out the appropriate numbers. 

Does anyone know of a better way? Using `map()`, maybe?

  [1]: http://desk.stinkpot.org:8080/tricks/index.php/2008/04/get-all-possible-combinations-of-a-lists-elements-in-python/


How to get all possible combinations of a list’s elements?

I am trying to capture &lt;kbd&gt;ctrl&lt;/kbd&gt;+&lt;kbd&gt;z&lt;/kbd&gt; key combination in javascript with this code:

    &lt;html&gt;
    &lt;head&gt;
        &lt;title&gt;Untitled Document&lt;/title&gt;
    &lt;/head&gt;
    &lt;body&gt;

        &lt;script type=&#39;text/javascript&#39;&gt;
            function KeyPress(e) {
                var evtobj = window.event? event : e


                //test1 if (evtobj.ctrlKey) alert(&quot;Ctrl&quot;);
                //test2 if (evtobj.keyCode == 122) alert(&quot;z&quot;);
                //test 1 &amp; 2
                if (evtobj.keyCode == 122 &amp;&amp; evtobj.ctrlKey) alert(&quot;Ctrl+z&quot;);
            }

            document.onkeypress = KeyPress;
        &lt;/script&gt;
    
    &lt;/body&gt;
    &lt;/html&gt;

Commented line &quot;test1&quot; generates the alert if I hold down the &lt;kbd&gt;ctrl&lt;/kbd&gt; key and press any other key.

Commented line &quot;test2&quot; generates the alert if I press the &lt;kbd&gt;z&lt;/kbd&gt; key.

Put them together as per the line after &quot;test 1 &amp; 2&quot;, and holding down the &lt;kbd&gt;ctrl&lt;/kbd&gt; key then pressing the &lt;kbd&gt;z&lt;/kbd&gt; key does not generate the alert as expected.

What is wrong with the code?

Capturing ctrl+z key combination in javascript

What is the Ruby way to achieve following?

    a = [1,2]
    b = [3,4]

I want an array: 

    =&gt; [f(1,3) ,f(1,4) , f(2,3) ,f(2,4)]

Combination of two arrays in Ruby

I have a need to create a list of combinations of numbers. The numbers are quite small so I can use `byte` rather than `int`. However it requires many nested loops in order to get every possible combination. I&#39;m wondering if there&#39;s a more efficient manner to do what I&#39;m after. Code so far is:

    var data = new List&lt;byte[]&gt;();
    for (byte a = 0; a &lt; 2; a++)
	for (byte b = 0; b &lt; 3; b++)
	for (byte c = 0; c &lt; 4; c++)
	for (byte d = 0; d &lt; 3; d++)
	for (byte e = 0; e &lt; 4; e++)
	for (byte f = 0; f &lt; 3; f++)
	for (byte g = 0; g &lt; 3; g++)
	for (byte h = 0; h &lt; 4; h++)
	for (byte i = 0; i &lt; 2; i++)
	for (byte j = 0; j &lt; 4; j++)
	for (byte k = 0; k &lt; 4; k++)
	for (byte l = 0; l &lt; 3; l++)
	for (byte m = 0; m &lt; 4; m++)
	{
		data.Add(new [] {a, b, c, d, e, f, g, h, i, j, k, l, m});
	}

I was considering using something like a `BitArray` but I&#39;m not sure how I could incorporate it.

Any recommendations would be greatly appreciated. Alternatively, perhaps this is the fastest way of doing what I want?

**EDIT**
Couple of quick points (and apologies I didn&#39;t put these in the original post):

 - The numbers and the order of them (2, 3, 4, 3, 4, 3, 3 etc) are very important, so using a solution such as [https://stackoverflow.com/questions/4319049/generating-permutations-using-linq] [1] won&#39;t help because the maximums in each &#39;column&#39; are different
 - I&#39;m not a mathematician, so I apologise if I&#39;m not using the technical terms like &#39;permutations&#39; and &#39;combinations&#39; correctly :)
 - I **do** need to populate all of these combinations at once - I can&#39;t just grab one or another based on an index
 - Using `byte` is faster than using `int`, I **guarantee** it. It&#39;s also a lot better on memory usage to have 67m+ arrays of bytes rather than ints
 - My ultimate goal here is to look for a faster alternative to nested loops.
 - I considered using parallel programming, but due to the iterative nature of what I&#39;m trying to achieve, I couldn&#39;t find a way to do it successfully (even with `ConcurrentBag`) - however I&#39;m happy to be proved wrong :)

  [1]: https://stackoverflow.com/questions/4319049/generating-permutations-using-linq

**CONCLUSION**

Caramiriel has provided a good micro-optimisation which shaves some time off the loops, so I&#39;ve marked that answer as correct. Eric also mentioned that it is faster to pre-allocate the List&lt;byte[]&gt;. But, at this stage it seems that the nested loops are in fact the fastest possible way of doing this (depressing, I know!).

If you want to try exactly what I was trying to benchmark with `StopWatch`, go with 13 loops counting up to 4 in each loop - that makes about 67m+ lines in the list. On my machine (i5-3320M 2.6GHz) it takes about 2.2s to do the optimised version.

Faster alternative to nested loops?

I&#39;m having trouble coming up with code to generate combinations from n number of arrays with m number of elements in them, in JavaScript. I&#39;ve seen similar questions about this for other languages, but the answers incorporate syntactic or library magic that I&#39;m unsure how to translate.

Consider this data:

	[[0,1], [0,1,2,3], [0,1,2]]

3 arrays, with a different number of elements in them. What I want to do is get all combinations by combining an item from each array.

For example:

	0,0,0 // item 0 from array 0, item 0 from array 1, item 0 from array 2
	0,0,1
	0,0,2
	0,1,0
	0,1,1
	0,1,2
	0,2,0
	0,2,1
	0,2,2

And so on.

If the number of arrays were fixed, it would be easy to make a hard coded implementation. But the number of arrays may vary:

	
	[[0,1], [0,1]]
	[[0,1,3,4], [0,1], [0], [0,1]]

Any help would be much appreciated.

JavaScript - Generating combinations from n arrays with m elements

I have been searching a source code for generating combination using c++. I found some advanced codes for this but that is good for only specific number predefined data. Can anyone give me some hints, or perhaps, some idea to generate combination. As an example, suppose the set S = { 1, 2, 3, ...., n} and we pick r= 2 out of it. The input would be `n` and `r`.In this case, the program will generate arrays of length two, like 5 2 outputs  1 2, 1 3, etc.. I had difficulty in constructing the algorithm. It took me a month thinking about this.


Generating combinations in c++

I am trying to generate all possible combinations of 0 and 1&#39;s in a vector of length 14. Is there an easy way of getting that output as a list of vectors, or even better, a dataframe?

To demonstrate better what I am looking for, let&#39;s suppose that I only want a vector of length 3. I would like to be able to generate the following:

     (1,1,1), (0,0,0), (1,1,0), (1,0,0), (1,0,1), (0,1,0), (0,1,1), (0,0,0)


Generate list of all possible combinations of elements of vector

Given an unknown amount of lists, each with an unknown length, I need to generate a singular list with all possible unique combinations.
For example, given the following lists:

    X: [A, B, C] 
    Y: [W, X, Y, Z]

Then I should be able to generate 12 combinations:

    [AW, AX, AY, AZ, BW, BX, BY, BZ, CW, CX, CY, CZ]

If a third list of 3 elements were added, I&#39;d have 36 combinations, and so forth.

Any ideas on how I can do this in Java?  
(pseudo code would be fine too)


Generate all combinations from multiple lists

What&#39;s the best algorithm to find all binary strings of length n that contain k bits set?  For example, if n=4 and k=3, there are...

    0111
    1011
    1101
    1110

I need a good way to generate these given any n and any k so I&#39;d prefer it to be done with strings.

Generate all binary strings of length n with k bits set

There are n people numbered from `1` to `n`. I have to write a code which produces and print all different combinations of `k` people from these `n`. Please explain the algorithm used for that. 

Creating all possible k combinations of n items in C++

I&#39;m basically looking for a python version of [Combination of `List&lt;List&lt;int&gt;&gt;`](https://stackoverflow.com/questions/545703/combination-of-listlistint)

Given a list of lists, I need a new list that gives all the possible combinations of items between the lists.

    [[1,2,3],[4,5,6],[7,8,9,10]] -&gt; [[1,4,7],[1,4,8],...,[3,6,10]]

The number of lists is unknown, so I need something that works for all cases. Bonus points for elegance!

All Combinations Solutions on Gang of Coders

Total of 20 Combinations Solutions