在较新的浏览器上，可以使用map或forEach来避免使用for循环.

On newer browsers, you can use map, or forEach which would avoid using a for loop.

var myArray = dataset.towns.map(function(town){
  return town[2];
});
// myArray == [[35.4,37.5], [35.8,37], [35.9,37.8]]

但是for循环更兼容.

But for loops are more compatible.

var myArray = [];
for(var i = 0, len = dataset.towns.length; i < len; i++){
  myArray.push(dataset.towns[i][2];
}