/* accept an array of stocks, pull out the symbol from each one of
those stocks, put the symbols in an array and return it */
/*
This process of applying some transformation to every item in an
array, and creating an array to hold all of the results is very common.
The Array has a map method which is used to make this even shorter.
*/
function getStockSymbols(stocks) {
//   var symbols = [];

//   /* forEach is really convenient if you want to do something
//   to every item in an array.
//   */
//   stocks.forEach(function(stock) {
//     symbols.push(stock.symbol);
//   });


// //   for(counter = 0; counter < stocks.length; counter++) {
// //     stock = stocks[counter];
// //     symbols.push(stock.symbol);
// //   }

//   return symbols;


  return stocks.map(function(stock) {
    return stock.symbol;
  });
}

// /* The whole job of the projection function is to transform the item in the array to something else
// */
// Array.prototype.map = function (projection) {
//   var results = [];

//   /*The reason we use this.forEach is that the map method is actually being added to the array itself. so this in the context of this funciton is an array. */
//   this.forEach( function(item) {
//     results.push(projection(item));
//   });

//   return results;
// };

var symbols = getStockSymbols([
  {symbol: "YHOO", price: 44.78, volume: 22000},
  {symbol: "AAPL", price: 102.68, volume: 25000},
  {symbol: "GOOG", price: 500.21, volume: 20000},
]);

console.log(JSON.stringify(symbols));