Turning an array to a special kind of object.

jtri_array_to_special_obj.js

//jtri: ok, can't quite wrap my head around this one: how do I turn [ [ 'mike', 'ryan' ], [ 'mike', 'jared' ], [ 'mike', 'jared' ] ] into {"mike": ["ryan", "jared", "jared"], "jared:["mike", "mike"], "ryan":["mike"]} ?

//from falafel 

// Helpers
var inArray = function(x) {
  return function(xs) {
    return xs.indexOf(x) > -1
  }
}
var notEq = function(x) {
  return function(y) {
    return x !== y
  }
}
var flatten = function(xs) {
  return xs.reduce(function(acc, x) {
    return acc.concat(x)
  }, [])
}
var unique = function(xs) {
  return xs.filter(function(x, i) {
    return xs.indexOf(x) == i
  })
}
var union = function(xs, ys) {
  return unique(flatten(xs.concat(ys)))
}

// Example
var xss =  [ [ 'mike', 'ryan' ], [ 'mike', 'jared' ], [ 'mike', 'jared' ] ]

var res = union.apply(null, xss)
  .reduce(function(acc, item) {
    acc[item] = flatten(xss.filter(inArray(item))).filter(notEq(item))
    return acc
  }, {})

console.log(res)