blocks|key|1535912|text|我最初建议在数组上使用select方法。也就是说：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1535913|[1,+2,+3,+4,+5,+6,+7].select{%7Ce%7C+e%252+==+0}把[2,4,6]还给我们了|1535914|但如果您想要第一个这样的对象，请使用detect。|1535915|[1,+2,+3,+4,+5,+6,+7].detect{%7Ce%7C+e>3}给了我们4。|1535916|不过，我不太清楚你来这里是为了什么。|1535917|entityMap^0|B|6|0|0|16|17|7|0|I|6|0|0|11|15|1|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|X|8|@$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|L|3|M|5|6|7|15|8|@]|D|@]|E|$]]|$1|N|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|O|$]]

I had originally suggested using the <code>select</code> method on Array. To wit:

<code>[1, 2, 3, 4, 5, 6, 7].select{|e| e%2 == 0}</code>
gives us <code>[2,4,6]</code> back.

But if you want the first such object, use <code>detect</code>.

<code>[1, 2, 3, 4, 5, 6, 7].detect{|e| e&gt;3}</code> gives us <code>4</code>.

I'm not sure what you're going for here, though.

blocks|key|1750849|text|如果我正确理解了您的问题，我已经使用比较封送对象以确定是否有任何属性变化的准hacky方法解决了这个问题。下面代码末尾的inject将是一个示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1750850|class+Foo
++attr_accessor+:foo,+:bar,+:baz

++def+initialize(foo,bar,baz)
++++@foo+=+foo
++++@bar+=+bar
++++@baz+=+baz
++end
end

objs+=+[Foo.new(1,2,3),Foo.new(1,2,3),Foo.new(2,3,4)]

#+find+objects+that+are+uniq+with+respect+to+attributes
objs.inject([])+do+%7Cuniqs,obj%7C
++if+uniqs.all?+{+%7Ce%7C+Marshal.dump(e)+!=+Marshal.dump(obj)+}
++++uniqs+<<+obj
++end
++uniqs
end|code-block|syntax|javascript|1750851|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

If I understand your question correctly, I've tackled this problem using the quasi-hacky approach of comparing the Marshaled objects to determine if any attributes vary. The inject at the end of the following code would be an example:

<pre><code>class Foo
 attr_accessor :foo, :bar, :baz

 def initialize(foo,bar,baz)
 @foo = foo
 @bar = bar
 @baz = baz
 end
end

objs = [Foo.new(1,2,3),Foo.new(1,2,3),Foo.new(2,3,4)]

# find objects that are uniq with respect to attributes
objs.inject([]) do |uniqs,obj|
 if uniqs.all? { |e| Marshal.dump(e) != Marshal.dump(obj) }
 uniqs &lt;&lt; obj
 end
 uniqs
end
</code></pre>

blocks|key|1750882|text|现在，如果您可以对属性值进行排序，则可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1750883|class+A
++attr_accessor+:val
++def+initialize(v);+self.val+=+v;+end
end

objs+=+[1,2,6,3,7,7,8,2,8].map{%7Ci%7C+A.new(i)}

objs.sort_by{%7Ca%7C+a.val}.inject([])+do+%7Cuniqs,+a%7C
++uniqs+<<+a+if+uniqs.empty?+%7C%7C+a.val+!=+uniqs.last.val
++uniqs
end|code-block|syntax|javascript|1750884|这是针对1属性唯一的，但同样的事情也可以用字典序排序来完成...|1750885|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Now if you can sort on the attribute values this can be done:

<pre><code>class A
 attr_accessor :val
 def initialize(v); self.val = v; end
end

objs = [1,2,6,3,7,7,8,2,8].map{|i| A.new(i)}

objs.sort_by{|a| a.val}.inject([]) do |uniqs, a|
 uniqs &lt;&lt; a if uniqs.empty? || a.val != uniqs.last.val
 uniqs
end
</code></pre>

That's for a 1-attribute unique, but the same thing can be done w/ lexicographical sort ...

blocks|key|1750907|text|在数据库级别执行此操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1750908|YourModel.find(:all,+:group+=>+"status")|code-block|syntax|javascript|1750909|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Do it on the database level:

<pre><code>YourModel.find(:all, :group =&gt; "status")
</code></pre>

blocks|key|1750931|text|您可以使用散列，每个键只包含一个值：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1750932|Hash[*recs.map{%7Car%7C+[ar[attr],ar]}.flatten].values|code-block|syntax|javascript|1750933|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can use a hash, which contains only one value for each key:

<pre><code>Hash[*recs.map{|ar| [ar[attr],ar]}.flatten].values
</code></pre>

blocks|key|1536062|text|将uniq_by方法添加到项目中的数组中。它的工作原理类似于sort_by。所以uniq_by之于uniq就像sort_by之于sort。用法：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1536063|uniq_array+=+my_array.uniq_by+{%7Cobj%7C+obj.id}|code-block|syntax|javascript|1536064|实现：|1536065|class+Array
++def+uniq_by(&blk)
++++transforms+=+[]
++++self.select+do+%7Cel%7C
++++++should_keep+=+!transforms.include?(t=blk[el])
++++++transforms+<<+t
++++++should_keep
++++end
++end
end|1536066|请注意，它返回一个新的数组，而不是修改当前的数组。我们还没有编写uniq_by!方法，但是如果您愿意的话，它应该很简单。|1536067|编辑:+Tribalvibes指出该实现是O(n%5E2)。更好的方法是这样(未测试)...|1536068|class+Array
++def+uniq_by(&blk)
++++transforms+=+{}
++++select+do+%7Cel%7C
++++++t+=+blk[el]
++++++should_keep+=+!transforms[t]
++++++transforms[t]+=+true
++++++should_keep
++++end
++end
end|1536069|entityMap^0|1|7|U|7|14|7|1D|4|1J|7|1S|4|0|0|0|0|W|8|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|19|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1A|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|1B|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1C|8|@$9|1D|A|1E|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1F|8|@]|D|@]|E|$]]|$1|S|3|T|5|H|7|1G|8|@]|D|@]|E|$I|J]]|$1|U|3|-4|5|6|7|1H|8|@]|D|@]|E|$]]]|V|$]]

Add the <code>uniq_by</code> method to Array in your project. It works by analogy with <code>sort_by</code>. So <code>uniq_by</code> is to <code>uniq</code> as <code>sort_by</code> is to <code>sort</code>. Usage:

<pre><code>uniq_array = my_array.uniq_by {|obj| obj.id}
</code></pre>

The implementation:

<pre><code>class Array
 def uniq_by(&amp;blk)
 transforms = []
 self.select do |el|
 should_keep = !transforms.include?(t=blk[el])
 transforms &lt;&lt; t
 should_keep
 end
 end
end
</code></pre>

Note that it returns a new array rather than modifying your current one in place. We haven't written a <code>uniq_by!</code> method but it should be easy enough if you wanted to.

EDIT: Tribalvibes points out that that implementation is O(n^2). Better would be something like (untested)...

<pre><code>class Array
 def uniq_by(&amp;blk)
 transforms = {}
 select do |el|
 t = blk[el]
 should_keep = !transforms[t]
 transforms[t] = true
 should_keep
 end
 end
end
</code></pre>

blocks|key|1751056|text|我喜欢jmah使用Hash来增强唯一性。下面是几种给猫剥皮的方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1751057|objs.inject({})+{%7Ch,e%7C+h[e.attr]=e;+h}.values|code-block|syntax|javascript|1751058|这是一个很好的1行代码，但我怀疑这可能会更快一些：|1751059|h+=+{}
objs.each+{%7Ce%7C+h[e.attr]=e}
h.values|1751060|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I like jmah's use of a Hash to enforce uniqueness. Here's a couple more ways to skin that cat:

<pre><code>objs.inject({}) {|h,e| h[e.attr]=e; h}.values
</code></pre>

That's a nice 1-liner, but I suspect this might be a little faster:

<pre><code>h = {}
objs.each {|e| h[e.attr]=e}
h.values
</code></pre>

blocks|key|1751106|text|Rails还有一个#uniq_by方法。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1751107|参考：Parameterized+Array#uniq+(i.e.,+uniq_by)|1751108|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/5251871/parameterized-arrayuniq-i-e-uniq-by^0|9|8|0|3|14|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@]|D|@$9|T|A|U|1|V]]|E|$]]|$1|H|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

Rails also has a <code>#uniq_by</code> method.

Reference: <a href="https://stackoverflow.com/questions/5251871/parameterized-arrayuniq-i-e-uniq-by">Parameterized Array#uniq (i.e., uniq_by)</a>

blocks|key|1536237|text|我喜欢jmah和Head的答案。但是它们能保持数组的顺序吗？在更高版本的ruby中可能会有，因为语言规范中已经写入了一些散列插入顺序保持要求，但这里有一个类似的解决方案，我喜欢使用它来保持顺序。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1536238|h+=+Set.new
objs.select{%7Cel%7C+h.add?(el.attr)}|code-block|syntax|javascript|1536239|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I like jmah and Head's answers. But do they preserve array order? They might in later versions of ruby since there have been some hash insertion-order-preserving requirements written into the language specification, but here's a similar solution that I like to use that preserves order regardless.

<pre><code>h = Set.new
objs.select{|el| h.add?(el.attr)}
</code></pre>

blocks|key|1536249|text|对块使用Array#uniq：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1536250|@photos+=+@photos.uniq+{+%7Cp%7C+p.album_id+}|code-block|syntax|javascript|1536251|entityMap|0|LINK|mutability|MUTABLE|url|http://ruby-doc.org/core-1.9.2/Array.html#method-i-uniq^0|4|A|4|A|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@$9|V|A|W|1|X]]|E|$]]|$1|F|3|G|5|H|7|Y|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

Use <a href="http://ruby-doc.org/core-1.9.2/Array.html#method-i-uniq" rel="noreferrer"><code>Array#uniq</code></a> with a block:

<pre><code>@photos = @photos.uniq { |p| p.album_id }
</code></pre>

blocks|key|1751227|text|ActiveSupport实现：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1751228|def+uniq_by
++hash,+array+=+{},+[]
++each+{+%7Ci%7C+hash[yield(i)]+%7C%7C=+(array+<<+i)+}
++array
end|code-block|syntax|javascript|1751229|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

ActiveSupport implementation:

<pre><code>def uniq_by
 hash, array = {}, []
 each { |i| hash[yield(i)] ||= (array &lt;&lt; i) }
 array
end
</code></pre>

blocks|key|1751255|text|您可以使用此技巧从数组中按多个属性元素选择唯一：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1751256|@photos+=+@photos.uniq+{+%7Cp%7C+[p.album_id,+p.author_id]+}|code-block|syntax|javascript|1751257|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can use this trick to select unique by several attributes elements from array:

<pre><code>@photos = @photos.uniq { |p| [p.album_id, p.author_id] }
</code></pre>

blocks|key|1536331|text|我发现的最优雅的方式是使用带有块的Array#uniq作为副产品|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1536332|enumerable_collection.uniq(&:property)|code-block|syntax|javascript|1536333|…它读起来也更好！|1536334|entityMap|0|LINK|mutability|MUTABLE|url|http://ruby-doc.org/core-1.9.2/Array.html#method-i-uniq^0|H|A|H|A|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|F|3|G|5|H|7|10|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|11|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

The most elegant way I have found is a spin-off using <a href="http://ruby-doc.org/core-1.9.2/Array.html#method-i-uniq" rel="nofollow noreferrer"><code>Array#uniq</code></a> with a block

<pre><code>enumerable_collection.uniq(&amp;:property)
</code></pre>

…it reads better too!

blocks|key|1536354|text|对块使用Array#uniq：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1536355|objects.uniq+{%7Cobj%7C+obj.attribute}|code-block|syntax|javascript|1536356|或者一种更简洁的方法：|1536357|objects.uniq(&:attribute)|1536358|entityMap|0|LINK|mutability|MUTABLE|url|http://ruby-doc.org/core-1.9.2/Array.html#method-i-uniq^0|4|A|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

Use <a href="http://ruby-doc.org/core-1.9.2/Array.html#method-i-uniq" rel="nofollow noreferrer">Array#uniq</a> with a block:

<pre><code>objects.uniq {|obj| obj.attribute}
</code></pre>

Or a more concise approach:

<pre><code>objects.uniq(&amp;:attribute)
</code></pre>

blocks|key|1751357|text|如果您还没有使用数组，我们还可以尝试通过set来消除重复项|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1751358|set+=+Set.new
set+<<+obj1
set+<<+obj2
set.inspect|code-block|syntax|javascript|1751359|请注意，对于自定义对象，我们需要覆盖eql?和hash方法|offset|length|style|CODE|1751360|entityMap^0|0|0|I|4|N|4|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]|$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|N|$]]

If you are not married with arrays, we can also try eliminating duplicates through sets
<pre><code>set = Set.new
set &lt;&lt; obj1
set &lt;&lt; obj2
set.inspect
</code></pre>
Note that in case of custom objects, we need to override <code>eql?</code> and <code>hash</code> methods

What's the most elegant way to select out objects in an array that are unique with respect to one or more attributes?

These objects are stored in ActiveRecord so using AR's methods would be fine too.

Uniq by object attribute in Ruby

对象存储

数据库

在数组中选择与一个或多个属性相关的唯一对象的最优雅的方法是什么？这些对象存储在ActiveRecord中，所以使用AR的方法也很好。

问Ruby中的Uniq by object属性
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