blocks|key|547923|text|我敢打赌肯定有一个！在Ruby中总是有一种更短的方法来做事情！|type|unstyled|depth|inlineStyleRanges|entityRanges|data|547924|这很简单，只需使用Hash#invert|offset|length|style|CODE|547925|{a:+:one,+b:+:two,+c:+:three}.invert
=>+{:one=>:a,+:two=>:b,+:three=>:c}|code-block|syntax|javascript|547926|就是这样！|547927|entityMap|0|LINK|mutability|MUTABLE|url|http://www.ruby-doc.org/core-1.9.3/Hash.html#method-i-invert^0|0|9|B|9|B|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@$D|Y|E|Z|F|G]]|9|@$D|10|E|11|1|12]]|A|$]]|$1|H|3|I|5|J|7|13|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|14|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]]]

You bet there is one! There is always a shorter way to do things in Ruby!

It's pretty simple, just use <a href="http://www.ruby-doc.org/core-1.9.3/Hash.html#method-i-invert"><code>Hash#invert</code></a>:

<pre><code>{a: :one, b: :two, c: :three}.invert
=&gt; {:one=&gt;:a, :two=&gt;:b, :three=&gt;:c}
</code></pre>

Et voilà!

blocks|key|331154|text|#+this+doesn't+looks+quite+as+elegant+as+the+other+solutions+here,
#+but+if+you+call+inverse+twice,+it+will+preserve+the+elements+of+the+original+hash

#+true+inversion+of+Ruby+Hash+/+preserves+all+elements+in+original+hash
#+e.g.+hash.inverse.inverse+~+h

class+Hash

++def+inverse
++++i+=+Hash.new
++++self.each_pair{+%7Ck,v%7C
++++++if+(v.class+==+Array)
++++++++v.each{+%7Cx%7C
++++++++++i[x]+=+i.has_key?(x)+?+[k,i[x]].flatten+:+k
++++++++}
++++++else
++++++++i[v]+=+i.has_key?(v)+?+[k,i[v]].flatten+:+k
++++++end
++++}
++++return+i
++end

end|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|331155|Hash#inverse为您提供了：|unstyled|offset|length|style|CODE|331156|+h+=+{a:+1,+b:+2,+c:+2}
+h.inverse
++=>+{1=>:a,+2=>[:c,+:b]}
+h.inverse.inverse
++=>+{:a=>1,+:c=>2,+:b=>2}++#+order+might+not+be+preserved
+h.inverse.inverse+==+h
++=>+true+++++++++++++++++++#+true-ish+because+order+might+change|331157|而内置的invert方法只是被破坏了：|331158|+h.invert
++=>+{1=>:a,+2=>:c}++++#+FAIL
+h.invert.invert+==+h+
++=>+false+++++++++++++#+FAIL|331159|entityMap^0|0|0|C|0|0|4|6|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|T|8|@$G|U|H|V|I|J]]|9|@]|A|$]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$B|C]]|$1|M|3|N|5|F|7|X|8|@$G|Y|H|Z|I|J]]|9|@]|A|$]]|$1|O|3|P|5|6|7|10|8|@]|9|@]|A|$B|C]]|$1|Q|3|-4|5|F|7|11|8|@]|9|@]|A|$]]]|R|$]]

<pre><code># this doesn't looks quite as elegant as the other solutions here,
# but if you call inverse twice, it will preserve the elements of the original hash

# true inversion of Ruby Hash / preserves all elements in original hash
# e.g. hash.inverse.inverse ~ h

class Hash

 def inverse
 i = Hash.new
 self.each_pair{ |k,v|
 if (v.class == Array)
 v.each{ |x|
 i[x] = i.has_key?(x) ? [k,i[x]].flatten : k
 }
 else
 i[v] = i.has_key?(v) ? [k,i[v]].flatten : k
 end
 }
 return i
 end

end
</code></pre>

<code>Hash#inverse</code> gives you:

<pre><code> h = {a: 1, b: 2, c: 2}
 h.inverse
 =&gt; {1=&gt;:a, 2=&gt;[:c, :b]}
 h.inverse.inverse
 =&gt; {:a=&gt;1, :c=&gt;2, :b=&gt;2} # order might not be preserved
 h.inverse.inverse == h
 =&gt; true # true-ish because order might change
</code></pre>

whereas the built-in <code>invert</code> method is just broken:

<pre><code> h.invert
 =&gt; {1=&gt;:a, 2=&gt;:c} # FAIL
 h.invert.invert == h 
 =&gt; false # FAIL
</code></pre>

blocks|key|548015|text|使用数组|type|unstyled|depth|inlineStyleRanges|entityRanges|data|548016|input+=+{:key1=>"value1",+:key2=>"value2",+:key3=>"value3",+:key4=>"value4",+:key5=>"value5"}
output+=+Hash[input.to_a.map{%7Cm%7C+m.reverse}]|code-block|syntax|javascript|548017|使用哈希|548018|input+=+{:key1=>"value1",+:key2=>"value2",+:key3=>"value3",+:key4=>"value4",+:key5=>"value5"}
output+=+input.invert|548019|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|$]]

Using Array

<pre><code>input = {:key1=&gt;"value1", :key2=&gt;"value2", :key3=&gt;"value3", :key4=&gt;"value4", :key5=&gt;"value5"}
output = Hash[input.to_a.map{|m| m.reverse}]
</code></pre>

Using Hash 

<pre><code>input = {:key1=&gt;"value1", :key2=&gt;"value2", :key3=&gt;"value3", :key4=&gt;"value4", :key5=&gt;"value5"}
output = input.invert
</code></pre>

blocks|key|331208|text|files+=+{
++'Input.txt'+=>+'Randy',
++'Code.py'+=>+'Stan',
++'Output.txt'+=>+'Randy'
}

h+=+Hash.new{%7Ch,k%7C+h[k]+=+[]}+#+Create+hash+that+defaults+unknown+keys+to+empty+an+empty+list
files.map+{%7Ck,v%7C+h[v]<<+k}+#append+each+key+to+the+list+at+a+known+value
puts+h|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|331209|这也将处理重复的值。|unstyled|331210|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>files = {
 'Input.txt' =&gt; 'Randy',
 'Code.py' =&gt; 'Stan',
 'Output.txt' =&gt; 'Randy'
}

h = Hash.new{|h,k| h[k] = []} # Create hash that defaults unknown keys to empty an empty list
files.map {|k,v| h[v]&lt;&lt; k} #append each key to the list at a known value
puts h
</code></pre>

This will handle the duplicate values too.

blocks|key|548097|text|如果您有一个散列，其中的键是唯一的，则可以使用Hash#invert|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|548098|>+{a:+1,+b:+2,+c:+3}.invert
=>+{1=>:a,+2=>:b,+3=>:c}+|code-block|syntax|javascript|548099|然而，如果你有非唯一的键，这将不起作用，其中只有最后看到的键将被保存：|548100|>+{a:+1,+b:+2,+c:+3,+d:+3,+e:+2,+f:+1}.invert
=>+{1=>:f,+2=>:e,+3=>:d}|548101|如果你有一个非唯一键的散列，你可以这样做：|548102|>+hash={a:+1,+b:+2,+c:+3,+d:+3,+e:+2,+f:+1}
>+hash.each_with_object(Hash.new+{+%7Ch,k%7C+h[k]=[]+})+{%7C(k,v),+h%7C+
++++++++++++h[v]+<<+k
++++++++++++}+++++
=>+{1=>[:a,+:f],+2=>[:b,+:e],+3=>[:c,+:d]}|548103|如果散列值已经是数组，您可以这样做：|548104|>+hash={+"A"+=>+[14,+15,+16],+"B"+=>+[17,+15],+"C"+=>+[35,+15]+}
>+hash.each_with_object(Hash.new+{+%7Ch,k%7C+h[k]=[]+})+{%7C(k,v),+h%7C+
++++++++++++v.map+{%7Ct%7C+h[t]+<<+k}
++++++++++++}+++
=>+{14=>["A"],+15=>["A",+"B",+"C"],+16=>["A"],+17=>["B"],+35=>["C"]}|548105|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.ruby-lang.org/en/2.4.0/Hash.html#method-i-invert^0|N|B|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@$A|13|B|14|1|15]]|C|$]]|$1|D|3|E|5|F|7|16|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|17|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|18|8|@]|9|@]|C|$G|H]]|$1|M|3|N|5|6|7|19|8|@]|9|@]|C|$]]|$1|O|3|P|5|F|7|1A|8|@]|9|@]|C|$G|H]]|$1|Q|3|R|5|6|7|1B|8|@]|9|@]|C|$]]|$1|S|3|T|5|F|7|1C|8|@]|9|@]|C|$G|H]]|$1|U|3|-4|5|6|7|1D|8|@]|9|@]|C|$]]]|V|$W|$5|X|Y|Z|C|$10|11]]]]

If you have a hash where are the keys are unique, you can use <a href="https://docs.ruby-lang.org/en/2.4.0/Hash.html#method-i-invert" rel="nofollow noreferrer">Hash#invert</a>:

<pre><code>&gt; {a: 1, b: 2, c: 3}.invert
=&gt; {1=&gt;:a, 2=&gt;:b, 3=&gt;:c} 
</code></pre>

That won't work if you have non unique keys, however, where only the last keys seen will be kept:

<pre><code>&gt; {a: 1, b: 2, c: 3, d: 3, e: 2, f: 1}.invert
=&gt; {1=&gt;:f, 2=&gt;:e, 3=&gt;:d}
</code></pre>

If you have a hash with non unique keys, you might do:

<pre><code>&gt; hash={a: 1, b: 2, c: 3, d: 3, e: 2, f: 1}
&gt; hash.each_with_object(Hash.new { |h,k| h[k]=[] }) {|(k,v), h| 
 h[v] &lt;&lt; k
 } 
=&gt; {1=&gt;[:a, :f], 2=&gt;[:b, :e], 3=&gt;[:c, :d]}
</code></pre>

If the values of the hash are already arrays, you can do:

<pre><code>&gt; hash={ "A" =&gt; [14, 15, 16], "B" =&gt; [17, 15], "C" =&gt; [35, 15] }
&gt; hash.each_with_object(Hash.new { |h,k| h[k]=[] }) {|(k,v), h| 
 v.map {|t| h[t] &lt;&lt; k}
 } 
=&gt; {14=&gt;["A"], 15=&gt;["A", "B", "C"], 16=&gt;["A"], 17=&gt;["B"], 35=&gt;["C"]}
</code></pre>

How do I swap keys and values in a Hash?

I have the following Hash:

<pre><code>{:a=&gt;:one, :b=&gt;:two, :c=&gt;:three}
</code></pre>

that I want to transform into:

<pre><code>{:one=&gt;:a, :two=&gt;:b, :three=&gt;:c}
</code></pre>

Using <code>map</code> seems rather tedious. Is there a shorter solution?

How to swap keys and values in a hash

如何在Hash中交换键和值？我有以下哈希：{:a=>:one, :b=>:two, :c=>:three}我想要转换成：{:one=>:a, :two=>:b, :three=>:c}使用map似乎相当乏味。有没有更短的解决方案？

问如何在散列中交换键和值
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