Looking at the difference between for loop, forEach, .map, & .filter methods + flattening arrays of arrays

js-async-examples.js

// // FIRST WAY
// // using a simple for loop
// function getStockSymbols(stocks) {
//   var results = [],
//       counter,
//       stock;
//
//   for (counter = 0; counter < stocks.length; counter++) {
//     stock = stocks[counter];
//     results.push(stock.symbol);
//   }
//
//   return results;
// }

// // SECOND WAY
// // using the es6 forEach iterator
// function getStockSymbols(stocks) {
//   // run forEach to iterate over array
//    var results = [];
//
//    stocks.forEach(function (stock) {
//       results.push(stock.symbol);
//    });
//
//    return results;
// }

// // THIRD WAY
// // using the .map method
// // map creates a new array
// function getStockSymbols(stocks) {
//
//   return stocks.map(function (stock) {
//      return stock.symbol;
//   });
// }

// var symbols = getStockSymbols([
//   { symbol: "XFX", price: 240.22, volume: 23432 },
//   { symbol: "TNZ", price: 332.19, volume: 234 },
//   { symbol: "JXJ", price: 120.22, volume: 5323 },
// ]);

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

// // FILTER FOR SPECIFIC ITEMS IN ARRAY
// // using .filter method
// // filter creates a new array
// function getStocksOver(stocks, minPrice) {
//     return stocks.filter(function(stock) {
//         return stock.price >= minPrice;
//     });
// }
//
// var expensiveStocks = getStocksOver([
//         { symbol: "XFX", price: 240.22, volume: 23432 },
//         { symbol: "TNZ", price: 332.19, volume: 234 },
//         { symbol: "JXJ", price: 120.22, volume: 5323 },
//     ],
//     150.00);
//
// console.log(JSON.stringify(expensiveStocks));

///////
// NEXT SECTION COMBINING THEM ALL TOGETHER
///////

// var stocks = [
//     { symbol: "XFX", price: 240.22, volume: 23432 },
//     { symbol: "TNZ", price: 332.19, volume: 234 },
//     { symbol: "JXJ", price: 120.22, volume: 5323 }
// ];
//
// var filteredStockSymbols =
//     stocks
//         // filter for only those stocks that are greater than or equal to 150
//         // filter returns a new array
//         .filter(function (stock) {
//            return stock.price >= 150.00;
//         })
//         // map returns a new array
//         .map(function (stock) {
//            return stock.symbol;
//         });
//
// filteredStockSymbols.forEach(function (symbol) {
//     console.log(symbol);
// });


////////////////
// ADDS NEW METHOD TO ARRAY PROTOTYPE TO LOOP THROUGH NESTED ARRAYS AND FLATTEN
////////////////

// var exchanges = [
//     [
//         { symbol: "XFX", price: 240.22, volume: 23432 },
//         { symbol: "TNZ", price: 332.19, volume: 234 }
//     ],
//     [
//         { symbol: "JXJ", price: 120.22, volume: 5323 },
//         { symbol: "NYN", price: 88.47, volume: 98275 }
//     ]
// ];
//
//
// Array.prototype.concatAll = function() {
//     var results = [];
//
//     this.forEach(function(subArray) {
//         subArray.forEach(function(item) {
//             results.push(item);
//         });
//     });
//
//     return results;
// };
//
//
// var stocks =  exchanges.concatAll();
//
// stocks.forEach(function(stock) {
//     console.log(JSON.stringify(stock));
// });


////////////////
// ADVANCED FLATTENING
////////////////
var exchanges = [
    {
        name: "NYSE",
        stocks: [
            {
                symbol: "XFX",
                closes: [
                    { date: new Date(2014,11,24), price: 240.10 },
                    { date: new Date(2014,11,23), price: 232.08 },
                    { date: new Date(2014,11,22), price: 241.09 }
                ]
            },
            {
                symbol: "TNZ",
                closes: [
                    { date: new Date(2014,11,24), price: 521.24 },
                    { date: new Date(2014,11,23), price: 511.00 },
                    { date: new Date(2014,11,22), price: 519.29 }
                ]
            }
        ]
    },
    {
        name: "TSX",
        stocks: [
            {
                symbol: "JXJ",
                closes: [
                    { date: new Date(2014,11,24), price: 423.22 },
                    { date: new Date(2014,11,23), price: 424.84 },
                    { date: new Date(2014,11,22), price: 419.72 }
                ]
            },
            {
                symbol: "NYN",
                closes: [
                    { date: new Date(2014,11,24), price: 16.82 },
                    { date: new Date(2014,11,23), price: 16.12 },
                    { date: new Date(2014,11,22), price: 15.77 }
                ]
            }
        ]
    }
];

Array.prototype.concatAll = function() {
    var results = [];

    this.forEach(function(subArray) {
        subArray.forEach(function(item) {
            results.push(item);
        });
    });

    return results;
};
//[1,2,3].map(function(num) { return num + 1; }) -> [2,3,4]
//[1,2].map(function(num) { return [num + 1, num + 2]; }) -> [[2,3],[3,4]]

var christmasEveCloses =
    exchanges.
    map(function(exchange) {
        return exchange.stocks.
        map(function(stock) {
            return stock.closes.
            filter(function(close) {
                return close.date.getMonth() === 11 &&
                    close.date.getDate() === 24;
            }).
            map(function(close) {
                return {
                    symbol: stock.symbol,
                    price: close.price
                };
            });
        }).
        concatAll();
    }).
    concatAll();

christmasEveCloses.forEach(function(christmasEveClose) {
    console.log(christmasEveClose);
});