独特的阵列COM prehension [英] Unique array comprehension

问题描述

我在CoffeeScript中下面的数组：

I have the following array in CoffeeScript:

electric_mayhem = [ { name: "Doctor Teeth", instrument: "piano" },
                { name: "Janice", instrument: "piano" },
                { name: "Sgt. Floyd Pepper", instrument: "bass" },
                { name: "Zoot", instrument: "sax" },
                { name: "Lips", instrument: "bass" },
                { name: "Animal", instrument: "drums" } ]

我的目标是从这个数组得到所有乐器名称。

My goal is to get all instrument names from this array.

预期结果： ['钢琴'，'噌'，'萨克斯'，'鼓']

我的第一个解决方案：

names = (muppet.instrument for muppet in electric_mayhem)
output = {}
output[name] = name for name in names
names = (value for key, value of output)

这是相当长的。我looket在transpiled JavaScript和看到的第一行被翻译成：

This is rather long. I looket at the transpiled javascript, and saw the first line is translated to:

names = (function() {
  var _i, _len, _results;
  _results = [];
  for (_i = 0, _len = electric_mayhem.length; _i < _len; _i++) {
    muppet = electric_mayhem[_i];
    _results.push(muppet.instrument);
  }
  return _results;
})();

所以我做了一个使用transpilation过程中引入了 _results 变量超级哈克解决方案：

So I made up a super-hacky solution that uses the _results variable introduced during transpilation:

names = (muppet.instrument for muppet in electric_mayhem \
  when muppet.instrument not in _results)

它的工作原理，但我不喜欢它依赖于未记录的变量名称，因此它可能会CoffeeScript的未来版本的破解。

It works, but I don't like it relies on not documented variable name so it may break with future releases of CoffeeScript.

有没有一个班轮在非哈克的方式来实现独一无二的COM prehension？

Is there any one-liner to achieve "unique comprehension" in a non-hacky way?

推荐答案

这一个班轮可能会做的伎俩：

This one-liner will probably do the trick:

names = (key for key of (new -> @[o.instrument] = '' for o in electric_mayhem; @))
//                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
//                                 "object comprehension"

至于自己，我（AB）利用关联数组使用它的键作为组唯一值的。

As yourself, I (ab)used an associative array to use its keys as the set of unique values.

不过，真正的招的这里采用的是一个对象COM prehension的构建阵列。或者至少，它最接近的等价形式目前市面上CoffeeScript的：

But, the real trick here is the use of an "object comprehension" to build that array. Or at least, its closest equivalent form currently available on CoffeeScript:

    (new -> @[o.instrument] = '' for o in electric_mayhem; @)
//   ^^^  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^  ^  
//  create                 with                            |
//  a new                  that                            |
//  empty                anonymous                         |
//  object               constructor                       |
//                                           don't forget -/
//                                           to return the
//                                        newly created object

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