invertByMany

invertByMany.js

// use lodash and es6 to invert a Object by subvalues. This let's you catalouge subvalues by keys

/** 
  * inverts a object by many values 
  * e.g. invertByMany({ 'a': [1,2,3], 'b': [1], c:[2]})
  * // {"1":["a","b"],"2":["a","c"],"3":["a"]}
  **/
 var invertByMany=(dataObj)=>
  _.transform(dataObj, (result, values, key)=>
      _.map(values,subvalue=>
        (result[subvalue] || (result[subvalue] = [])).push(key))
  , {})


/**
 * inverts a object by many unique values
 * inveryByUniqueValues({ 'a': [1,2], 'b': [3], c:[4]})
 * // {1: "a", 2: "a", 3: "b", 4:"c"}
 */
export var invertByUniqueValues = function (dataObj) {
    return _.transform(dataObj, (a, v, k) =>
        _.map(v, sv => a[sv] = k), {})
}

// P.S.
// es5 version of invertByMany
function invertByMany(dataObj){
  return _.transform(dataObj, function(result, values, key){
      return _.map(values,function(subvalue){
        if (!result[subvalue]) result[subvalue] = []
        result[subvalue].push(key)
        return result;
      })
  }, {});
}