哈希的简单打印键？

Question

我想从给定的哈希键打印一个键,但我找不到一个简单的解决方案:

myhash = Hash.new
myhash["a"] = "bar"

# not working
myhash.fetch("a"){|k|  puts k } 

# working, but ugly
if myhash.has_key("a")?
    puts "a"
end

还有其他方法吗？

Answer 1

要从哈希中获取所有密钥,请使用keys方法:

{ "1" => "foo", "2" => "bar" }.keys
=> ["1", "2"]

Answer 2

我知道这是一个较老的问题,但我认为最初的提问者想要的是在他不知道它是什么时找到钥匙; 例如,在迭代哈希时.

获取哈希键的其他几种方法:

给定哈希定义:

myhash = Hash.new
myhash["a"] = "Hello, "
myhash["b"] = "World!"

你第一次尝试不起作用的原因:

#.fetch just returns the value at the given key UNLESS the key doesn't exist
#only then does the optional code block run.
myhash.fetch("a"){|k|  puts k } 
#=> "Hello!" (this is a returned value, NOT a screen output)
myhash.fetch("z"){|k|  puts k } 
#z  (this is a printed screen output from the puts command)
#=>nil   (this is the returned value)

因此,如果您想在迭代哈希时获取密钥:

#when pulling each THEN the code block is always run on each result.
myhash.each_pair {|key,value| puts "#{key} = #{value}"}
#a = Hello, 
#b = World!

如果你只是进入单行并希望:

获取给定密钥的密钥(不知道为什么,因为您已经知道密钥):

myhash.each_key {|k| puts k if k == "a"}
#a

获取给定值的密钥:

myhash.each_pair {|k,v| puts k if v == "Hello, "} 
#a

Answer 3

我不太明白.如果你已经知道你想要puts的价值"a",那么你只需要puts "a".

有意义的是搜索给定值的键,如下所示:

puts myhash.key 'bar'
=> "a"

或者,如果未知密钥是否存在于哈希中,并且您希望仅在它存在时才打印它:

puts "a" if myhash.has_key? "a"