ruby的hash学习笔记例： 将字符串文本中的单词存放在map中

text = 'The rain in Spain falls mainly in the plain.'
first = Hash.new []
second = Hash.new  {|hash,key| hash[key] = []}

text.split(/\W+/).each do |word|
  p "word: #{word}"
  p first[word[0, 1].downcase].object_id
  first[word[0, 1].downcase] << word
  p first[word[0, 1].downcase]
end
p first

"word: The"
46999283958220  这里是关键。每次都是引用同一个数组。
["The"]
"word: rain"
46999283958220
["The", "rain"]
"word: in"
46999283958220
["The", "rain", "in"]
"word: Spain"
46999283958220
["The", "rain", "in", "Spain"]
"word: falls"
46999283958220
["The", "rain", "in", "Spain", "falls"]
"word: mainly"
46999283958220
["The", "rain", "in", "Spain", "falls", "mainly"]
"word: in"
46999283958220
["The", "rain", "in", "Spain", "falls", "mainly", "in"]
"word: the"
46999283958220
["The", "rain", "in", "Spain", "falls", "mainly", "in", "the"]
"word: plain"
46999283958220
["The", "rain", "in", "Spain", "falls", "mainly", "in", "the", "plain"]
{}

text.split(/\W+/).each do |word|
  p "word: #{word}"
  p second[word[0, 1].downcase].object_id
  second[word[0, 1].downcase] << word
  p second[word[0, 1].downcase]
end
p second

"word: The"
46999283949940
["The"]
"word: rain"
46999283924940  这里按照key取，不同的key对应不同的数组
["rain"]
"word: in"
46999283924440
["in"]
"word: Spain"
46999283923920
["Spain"]
"word: falls"
46999283923420
["falls"]
"word: mainly"
46999283922920
["mainly"]
"word: in"
46999283924440
["in", "in"]
"word: the"
46999283949940
["The", "the"]
"word: plain"
46999283921440
["plain"]
{"t"=>["The", "the"], "r"=>["rain"], "i"=>["in", "in"], "s"=>["Spain"], "f"=>["falls"], "m"=>["mainly"], "p"=>["plain"]}