如何使用数组中的键初始化哈希？

How to initialize a hash with keys from an array like the following?

如何使用数组中的键初始化哈希,如下所示?

keys = [ 'a' , 'b' , 'c' ]

Desired hash h should be:

期望的哈希值应该是:

puts h 
# { 'a' => nil , 'b' => nil , 'c' => nil }

5 个解决方案

#1

Here we go using Enumerable#each_with_object and Hash::[].

这里我们使用Enumerable#each_with_object和Hash :: []。

 keys = [ 'a' , 'b' , 'c' ]
 Hash[keys.each_with_object(nil).to_a]
 # => {"a"=>nil, "b"=>nil, "c"=>nil}

or Using Array#product

或使用Array#product

keys = [ 'a' , 'b' , 'c' ]
Hash[keys.product([nil])]
# => {"a"=>nil, "b"=>nil, "c"=>nil}

#2

Another alternative using Array#zip:

另一种使用Array#zip的替代方案:

Hash[keys.zip([])]
# => {"a"=>nil, "b"=>nil, "c"=>nil}

Update: As suggested by Arup Rakshit here's a performance comparison between the proposed solutions:

更新:根据Arup Rakshit的建议,这里提出的解决方案之间的性能比较:

require 'fruity'

ary = *(1..10_000)

compare do
  each_with_object {  ary.each_with_object(nil).to_a  }
  product          {  ary.product([nil])  }
  zip              {  ary.zip([])  }
  map              {  ary.map { |k| [k, nil] }  }
end

The result:

Running each test once. Test will take about 1 second.
zip is faster than product by 19.999999999999996% ± 1.0%
product is faster than each_with_object by 30.000000000000004% ± 1.0%
each_with_object is similar to map

#3

Using the new (Ruby 2.1) to_h:

使用新的(Ruby 2.1)to_h:

keys.each_with_object(nil).to_h

#4

=> keys = [ 'a' , 'b' , 'c' ]
=> Hash[keys.map { |x, z| [x, z] }]
# {"a"=>nil, "b"=>nil, "c"=>nil}

=> Hash[keys.map { |x| [x, nil] }]
# {"a"=>nil, "b"=>nil, "c"=>nil}

=> Hash[keys.map { |x, _| [x, _] }]
# {"a"=>nil, "b"=>nil, "c"=>nil}

#5

I think you should try:

我想你应该试试:

x = {}
keys.map { |k, _| x[k.to_s] = _ }

#1