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  <title>JS Bin</title>
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<script id="jsbin-javascript">
//finds the symmetric difference between a series of arrays

"use strict";

function symDiff() {
  for (var _len = arguments.length, args = Array(_len), _key = 0; _key < _len; _key++) {
    args[_key] = arguments[_key];
  }

  //loop through arrays
  return args.reduce(function (symDiff, arr, i) {
    //dedupe arr
    //use object keys to dedupe
    var dedupeObj = arr.reduce(function (obj, num) {
      obj[num] = "I can't get no";
      return obj;
    }, {});
    //reform array from obj keys
    arr = Object.keys(dedupeObj).map(function (key) {
      return parseInt(key);
    });
    //merge two arrays
    symDiff = symDiff.concat(arr);
    //count instances of values by using obj keys to dedupe
    var countObj = symDiff.reduce(function (obj, num) {
      obj[num] = ++obj[num] || 1;
      return obj;
    }, {});
    console.log({ countObj: countObj });
    //convert keys that have a value of 1 into array
    var uniques = [];
    for (key in countObj) {
      if (countObj[key] === 1) {
        uniques.push(parseInt(key));
      }
    }
    return uniques;
  }, []);
}

var result = symDiff([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3]);
console.log(result);

//[2, 3, 4, 6, 7]
</script>


<script id="jsbin-source-javascript" type="text/javascript">//finds the symmetric difference between a series of arrays

function symDiff(...args) {
  //loop through arrays
  return args.reduce( (symDiff , arr, i) => {
    //dedupe arr
    //use object keys to dedupe
    const dedupeObj = arr.reduce( (obj, num) => {
      obj[num] = "I can't get no";
      return obj;
    }, {});
    //reform array from obj keys
    arr = Object.keys(dedupeObj).map( (key) => parseInt(key));
    //merge two arrays
    symDiff = symDiff.concat(arr);
    //count instances of values by using obj keys to dedupe
    const countObj = symDiff.reduce( (obj, num) => {
      obj[num] = ++obj[num] || 1;
      return obj;
    }, {});
    console.log({countObj});
    //convert keys that have a value of 1 into array
    const uniques = [];
    for (key in countObj) {
      if (countObj[key] === 1) {uniques.push(parseInt(key));}
    }
    return uniques;
  }, []);
}

const result = symDiff([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3]);
console.log(result);


//[2, 3, 4, 6, 7]</script></body>
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