offer class preferences code

app.js

//var prefs = [[2,3],[1,3],[1,2],[5,6],[4,6],[4,5],[8,9],[7,9],[7,8],[11,12],[10,12],[10,11],[14,15],[13,15],[13,14],[17,18],[16,18],[16,17]];

var perfstr = `1	13	16
2	13	18
3	7	10
4	11	16
5	6	9
6	13	5
7	5	6
8	-1 	-1 
9	11	12
10	11	12
11	4	10
12	18	17
13	1	6
14	5	9
15	17	18
16	1	13
17	18	10
18	15	17`;

var prefs = perfstr.split('\n').map(x=>x.split('\t')).map(x=>[parseInt(x[1]),parseInt(x[2])])

var getAllSubsets = 
      theArray => theArray.reduce(
        (subsets, value) => subsets.concat(
         subsets.map(set => [value,...set])
        ),
        [[]]
      );

var all = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18];

var nines = getAllSubsets(all).filter(subset=>subset.length === 9)

var groups = nines.map(subset=>{
return [subset, all.map(x => subset.indexOf(x) === -1 ? x : null).filter(x=>!!x)]
});

var scores = groups.map(([arr1,arr2])=>{
return [{arr:arr1, score:arr1.map((x)=>{

var p1 = arr1.indexOf(prefs[x-1][0]) !== -1 ? 1 : 0;
var p2 = arr1.indexOf(prefs[x-1][1]) !== -1 ? 1 : 0;
return p1 + p2;

}).reduce((a, b) => a + b, 0)},
        {arr: arr2, score: arr2.map((x)=>{

var p1 = arr2.indexOf(prefs[x-1][0]) !== -1 ? 1 : 0;  // pref 1 score, for now 1
var p2 = arr2.indexOf(prefs[x-1][1]) !== -1 ? 1 : 0;  // pref 2 score, for now 2
return p1 + p2;

}).reduce((a, b) => a + b, 0)}]
})

scores.sort((a,b)=>((b[0].score + b[1].score) - (a[0].score + a[1].score) ))

console.log(scores)