How to generate combinations from arrays?

Question

Consider the case of having three arrays:

X = {A , B , C};
Y = {D , E , F};
Z = {G , H , I};

How to generate all the possible combinations from these three arrays ( C++ or Python ), that's like

C1 = {A , D , G};
C2 = {A , D , H};
...
C4 = {A, E , G};
...
C10 = {B , D , G};
...
...

I think you are looking for cartesian product. Look here .https://stackoverflow.com/questions/533905/get-the-cartesian-product-of-a-series-of-lists — Alex, Sep 04 '17 at 01:37
@Tico Thank you This is exactly what I was looking for.. If there is a c++ implementation it would be great too. — Omar Farrag, Sep 04 '17 at 01:49
@Julien Thank you This is exactly what I was looking for.. If there is a c++ implementation it would be great too. — Omar Farrag, Sep 04 '17 at 01:50

nos · Accepted Answer · 2017-09-04T11:16:18.860

2

Try this

from itertools import product

x = {'a', 'b', 'c'}
y = {'d', 'e', 'f'}
z = {'g', 'h', 'i'}

for a in product(x, y, z):
    print(a)

If you want to be more down-to-earth, getting all combinations from multiple sets can be done by nested loops. In python, it would be like this

for e1 in x:
    for e2 in y:
        for e3 in z:
            print((e1, e2, e3))

If you do not know how many iterables exist beforehand, you can keep appending them into a list as the program runs, then run product(*args), for example

items = [x, y]
items.append(z)
for a in product(*items):
    print(a)

edited Sep 04 '17 at 11:16

answered Sep 04 '17 at 01:39

nos

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What if I don't know the input arrays until run time ? – Omar Farrag Sep 04 '17 at 01:51
I mean I don't know how many arrays I will be working with – Omar Farrag Sep 04 '17 at 02:34

score 0 · Answer 2 · answered Sep 04 '17 at 02:40

You can use Algorithm header inside STL, Using next_permutation function you can generate all possible combination. Caution: It will only generate one permutation, You will have to use it inside a loop. You can see the documentation for the function on this link.Generating Permutation

score 0 · Answer 3 · answered Sep 04 '17 at 02:43

The "combination" function works recursively to find the answer. Just put all your elements in an array called "arr" which I considered that has the size of 6. Below is an example on haw to use the function:

#include <iostream>
#include <vector>
using namespace std;


void combinations(string arr[], int len, int startPosition, string result[]){
    if (len == 0){
        cout <<"{";
        for (int i = 0; i < 2; i++) {
            cout << result[i] <<", ";
        }
        cout << result[2]+ "}" << endl;
        return;
    }

    for (int i = startPosition; i <= 6-len; i++){
        result[3 - len] = arr[i];
        combinations(arr, len-1, i+1, result);
    }
}

int main(int argc, const char * argv[]) {

    string arr[] = {"A","B","C","D","E","F"};
    string temp[3];
    combinations(arr, 3, 0, temp);

}

How to generate combinations from arrays?

3 Answers3