function _ElementDiff (obj1, obj2) {
    // Convert matrices to arrays
    if (isMatrix(obj1)) obj1 = obj1.toArray()
    if (isMatrix(obj2)) obj2 = obj2.toArray()

    const obj1IsArray = Array.isArray(obj1)
    const obj2IsArray = Array.isArray(obj2)
    if (obj1IsArray && obj2IsArray) {
      return _ArrayDiff(obj1, obj2)
    }
    if (!obj1IsArray && !obj2IsArray) {
      return subtract(obj2, obj1) // Difference is (second - first) NOT (first - second)
    }
    throw TypeError('Cannot calculate difference between 1 array and 1 non-array')
  }
Difference between 2 objects

@param {Object} obj1    First object
@param {Object} obj2    Second object
@return {Array}         resulting array