JavaScript 按数组分组 [英] JavaScript Group By Array

问题描述

可能的重复:
array_count_values 代替javascript

假设我有一个简单的 JavaScript 数组，如下所示:

Let's say I have simple JavaScript array like the following:

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

我想对每个进行分组和计数，所以我希望有一个键/值映射:

I want to group and count of each so I would expect a key/value map of:

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

推荐答案

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 }

这也有效:

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

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