JavaScript 按数组分组

Question

Possible Duplicate:
array_count_values for javascript instead

假设我有如下简单的 JavaScript 数组:

var array = ['Car', 'Car', 'Truck', 'Boat', 'Truck'];

我想对每个进行分组和计数，因此我希望有一个键/值映射:

{
  Car   : 2,
  Truck : 2,
  Boat  : 1
}

Answer 1

var arr = [ 'Car', 'Car', 'Truck', 'Boat', 'Truck' ];
var hist = {};
arr.map( function (a) { if (a in hist) hist[a] ++; else hist[a] = 1; } );
console.log(hist);

结果

{ Car: 2, Truck: 2, Boat: 1 }

这也行:

hist = arr.reduce( function (prev, item) { 
  if ( item in prev ) prev[item] ++; 
  else prev[item] = 1; 
  return prev; 
}, {} );