Question

我在Ruby中使用散列哈希，名为MYMOVIES，如下所示。

    {"127 Hours"=>
       {"title"=>"127 Hours",
       "year"=>"2010",
       "plays"=>1,
       "last_played"=>1300489200,
       "seen_date"=>"19/3/2011",
       "imdb_id"=>"tt1542344",
       "rating"=>"6",
       "omdbapiurl"=>"http://www.omdbapi.com/?t=127 Hours&y=2010"},
    "Zombieland"=>
       {"title"=>"Zombieland",
       "year"=>"2009",
       "plays"=>1,
       "last_played"=>1290207600,
       "seen_date"=>"20/11/2010",
       "imdb_id"=>"tt1156398",
       "rating"=>"7",
       "omdbapiurl"=>"http://www.omdbapi.com/?t=Zombieland&y=2009"}}

现在，我想获得第一个嵌套哈希的所有键（即title，year，plays，...，omdbapiurl）。

我尝试过：

   mynestedhash = MYMOVIES.first
   puts mynestedhash.keys.to_s

但我收到错误：

    undefined method `keys' for #<Array:0x801c56f8> (NoMethodError)

我该怎么办？

Answer 1

这应该做：

MYMOVIES.map { |_, h| h.keys }.flatten.uniq
# => ["title", "year", "plays", "last_played", "seen_date", "imdb_id", "rating", "omdbapiurl"]

您的代码无效，因为方法first返回一个数组，而不是哈希：

MYMOVIES.first
# => ["127 Hours", {"title"=>"127 Hours", ... }]]

更新如果您想获取第一个哈希的密钥，那么您可以这样做：

nested_hash = MYMOVIES.first[1]
nested_hash.keys
# => ["title", "year", "plays", "last_played", "seen_date", "imdb_id", "rating", "omdbapiurl"]

或者：

_, nested_hash = MYMOVIES.first
nested_hash.keys
# => ["title", "year", "plays", "last_played", "seen_date", "imdb_id", "rating", "omdbapiurl"]

Answer 2

如果所有内部哈希值都具有相同的键，则以下内容就足够了

first_outer_key, first_outer_value = MYMOVIES.first 
first_inner_hash = first_outer_value # change name to show what we have
inner_keys = first_inner_hash.keys

如果内部哈希的键可能不同，则应加入它们就像Priti和toro2k在他们的解决方案中所做的那样。

Answer 3

require 'pp'
h = {"127 Hours"=>
       {"title"=>"127 Hours",
       "year"=>"2010",
       "plays"=>1,
       "last_played"=>1300489200,
       "seen_date"=>"19/3/2011",
       "imdb_id"=>"tt1542344",
       "rating"=>"6",
       "omdbapiurl"=>"http://www.omdbapi.com/?t=127 Hours&y=2010"},
    "Zombieland"=>
       {"title"=>"Zombieland",
       "year"=>"2009",
       "plays"=>1,
       "last_played"=>1290207600,
       "seen_date"=>"20/11/2010",
       "imdb_id"=>"tt1156398",
       "rating"=>"7",
       "omdbapiurl"=>"http://www.omdbapi.com/?t=Zombieland&y=2009"}}

pp h.flat_map{|k,v| v.keys}.uniq

<强>输出

["title",
 "year",
 "plays",
 "last_played",
 "seen_date",
 "imdb_id",
 "rating",
 "omdbapiurl"]

现在看看你的代码在下面不起作用的原因：

h = {"127 Hours"=>
       {"title"=>"127 Hours",
       "year"=>"2010",
       "plays"=>1,
       "last_played"=>1300489200,
       "seen_date"=>"19/3/2011",
       "imdb_id"=>"tt1542344",
       "rating"=>"6",
       "omdbapiurl"=>"http://www.omdbapi.com/?t=127 Hours&y=2010"},
    "Zombieland"=>
       {"title"=>"Zombieland",
       "year"=>"2009",
       "plays"=>1,
       "last_played"=>1290207600,
       "seen_date"=>"20/11/2010",
       "imdb_id"=>"tt1156398",
       "rating"=>"7",
       "omdbapiurl"=>"http://www.omdbapi.com/?t=Zombieland&y=2009"}}

h.first
#["127 Hours",
# {"title"=>"127 Hours",
# "year"=>"2010",
# "plays"=>1,
# "last_played"=>1300489200,
# "seen_date"=>"19/3/2011",
# "imdb_id"=>"tt1542344",
# "rating"=>"6",
# "omdbapiurl"=>"http://www.omdbapi.com/?t=127 Hours&y=2010"}]
p h.first.grep /keys/
#[]

现在很明显，从#grep方法来看，Array没有keys方法。因此，请尝试使用上面的代码使其可行。

散列哈希，如何获取第一个嵌套散列的键

3 个答案: