Get all possible combination from an arraylist of arraylist of an object

Question

I want to extract all possible combination from the following
the array list that holds all the data has this structure

ArrayList<object> students = new ArrayList<object>();
ArrayList<object> staff = new ArrayList<object>();
ArrayList<object> uni = new ArrayList<object>();
ArrayList<object> exam = new ArrayList<object>();

ArrayList<ArrayList<object>> main = new ArrayList<object>();
main.add(this.students);
main.add(this.staff);
main.add(this.uni);
main.add(this.exam);

class object has but two variables

class object {
    public String name; 
    public double cost;
}

this main variable hold the following data as indicated in the table and each column might have from 1 to 100 value but that doesn't mean that each column must have the same number of values

| students | staff | uni---| exam |
|500--------|400--|1400 |20000 |
|350--------|250--|1100 |10000 |

So what I want to extract is something like that
500=>400=>1400=>20000
500=>400=>1400=>10000

500=>400=>1100=>20000
500=>400=>1100=>10000

500=>250=>1400=>20000
500=>250=>1400=>10000

500=>250=>1100=>20000
500=>250=>1100=>10000

350=>400=>1400=>20000
350=>400=>1400=>10000

350=>400=>1100=>20000
350=>400=>1100=>10000

350=>250=>1400=>20000
350=>250=>1400=>10000

350=>250=>1100=>20000
350=>250=>1100=>10000

how can I do that?

class object { Please name your classes appropriately. This is unacceptable in the Java world. — Qix - MONICA WAS MISTREATED
– Qix - MONICA WAS MISTREATED, Commented Mar 18, 2017 at 18:35
i just name it this way because I'm trying to achieve something here and I don't need any naming convention because this is just a test of my code — hamada147
– hamada147, Commented Mar 18, 2017 at 19:27

lazyc97 · Accepted Answer · 2017-03-18 18:33:59Z

2

How about a simple recursive function like this ?

ArrayList<ArrayList<object>> combs = new ArrayList<>();
object[] comb = new object[main.size()];

void generate(int pos) {
    if (pos == comb.length)
        combs.add(new ArrayList<object>(Arrays.asList(comb)));
    else {
        ArrayList<object> arr = main.get(pos);
        for (object el : arr) {
            comb[pos] = el;
            generate(pos + 1);
        }
    }
}

answered Mar 18, 2017 at 18:33

lazyc97

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