var csv = [
  "name,birthday_day,birthday_month,birthday_year,house_type,house_address_street,house_address_city,house_address_state,house_occupants",
  "Lily Haywood,27,3,1995,Igloo,768 Pocket Walk,Honolulu,HI,7",
  "Stan Marsh,19,10,1987,Treehouse,2001 Bonanza Street,South Park,CO,2"
];

var attrs = csv.splice(0,1);

var result = csv.map(function(row) {
  var obj = {};
  var rowData = row.split(',');
  attrs[0].split(',').forEach(function(val, idx) {
    obj = constructObj(val, obj, rowData[idx]);
  });
  return obj;
})


function constructObj(str, parentObj, data) {
  if(str.split('_').length === 1) {
    parentObj[str] = data;
    return parentObj;
  }

  var curKey = str.split('_')[0];
  if(!parentObj[curKey])
    parentObj[curKey] = {};
  parentObj[curKey] = constructObj(str.split('_').slice(1).join('_'), parentObj[curKey], data);
  return parentObj;
}

return result;