如何计算Ruby数组中相同的string元素
我有以下Array = ["Jason", "Jason", "Teresa", "Judah", "Michelle", "Judah", "Judah", "Allison"]
我如何计算每个相同的元素 ？
Where: "Jason" = 2, "Judah" = 3, "Allison" = 1, "Teresa" = 1, "Michelle" = 1?
或产生一个散列其中：
其中：hash = {“Jason”=> 2，“Judah”=> 3，“Allison”=> 1，“Teresa”=> 1，“Michelle”=> 1}
names = ["Jason", "Jason", "Teresa", "Judah", "Michelle", "Judah", "Judah", "Allison"] counts = Hash.new(0) names.each { |name| counts[name] += 1 } # => {"Jason" => 2, "Teresa" => 1, ....
names.inject(Hash.new(0)) { |total, e| total[e] += 1 ;total}
给你
{"Jason"=>2, "Teresa"=>1, "Judah"=>3, "Michelle"=>1, "Allison"=>1}
现在使用Ruby 2.2.0，你可以利用itself方法 。
names = ["Jason", "Jason", "Teresa", "Judah", "Michelle", "Judah", "Judah", "Allison"] counts = {} names.group_by(&:itself).each { |k,v| counts[k] = v.length } # counts > {"Jason"=>2, "Teresa"=>1, "Judah"=>3, "Michelle"=>1, "Allison"=>1}
实际上有一个这样的数据结构： MultiSet 。
不幸的是，在Ruby核心库或标准库中没有MultiSet实现，但是在Web上有几个实现。
这是数据结构select如何简化algorithm的一个很好的例子。 事实上，在这个特定的例子中，algorithm甚至完全消失。 这实际上只是：
Multiset.new(*names)
就是这样。 例如，使用https://GitHub.Com/Josh/Multimap/ ：
require 'multiset' names = %w[Jason Jason Teresa Judah Michelle Judah Judah Allison] histogram = Multiset.new(*names) # => #<Multiset: {"Jason", "Jason", "Teresa", "Judah", "Judah", "Judah", "Michelle", "Allison"}> histogram.multiplicity('Judah') # => 3
例如，使用http://maraigue.hhiro.net/multiset/index-en.php ：
require 'multiset' names = %w[Jason Jason Teresa Judah Michelle Judah Judah Allison] histogram = Multiset[*names] # => #<Multiset:#2 'Jason', #1 'Teresa', #3 'Judah', #1 'Michelle', #1 'Allison'>
Enumberable#each_with_object返回最后一个散列。
names.each_with_object(Hash.new(0)) { |name, hash| hash[name] += 1}
返回：
=> {"Jason"=>2, "Teresa"=>1, "Judah"=>3, "Michelle"=>1, "Allison"=>1}
这工作。
arr = ["Jason", "Jason", "Teresa", "Judah", "Michelle", "Judah", "Judah", "Allison"] result = {} arr.uniq.each{|element| result[element] = arr.count(element)}
以下是一个稍微有些function的编程风格：
array_with_lower_case_a = ["Jason", "Jason", "Teresa", "Judah", "Michelle", "Judah", "Judah", "Allison"] hash_grouped_by_name = array_with_lower_case_a.group_by {|name| name} hash_grouped_by_name.map{|name, names| [name, names.length]} => [["Jason", 2], ["Teresa", 1], ["Judah", 3], ["Michelle", 1], ["Allison", 1]]
group_by一个优点是你可以使用它来分组等效但不完全相同的项目：
another_array_with_lower_case_a = ["Jason", "jason", "Teresa", "Judah", "Michelle", "Judah Ben-Hur", "JUDAH", "Allison"] hash_grouped_by_first_name = another_array_with_lower_case_a.group_by {|name| name.split(" ").first.capitalize} hash_grouped_by_first_name.map{|first_name, names| [first_name, names.length]} => [["Jason", 2], ["Teresa", 1], ["Judah", 3], ["Michelle", 1], ["Allison", 1]]
names = ["Jason", "Jason", "Teresa", "Judah", "Michelle", "Judah", "Judah", "Allison"] Hash[names.group_by{|i| i }.map{|k,v| [k,v.size]}] # => {"Jason"=>2, "Teresa"=>1, "Judah"=>3, "Michelle"=>1, "Allison"=>1}
a = [1, 2, 3, 2, 5, 6, 7, 5, 5] a.each_with_object(Hash.new(0)) { |o, h| h[o] += 1 } # => {1=>1, 2=>2, 3=>1, 5=>3, 6=>1, 7=>1}
信用弗兰克Wambutt
这更多的是评论而不是答案，但评论不会公正。 如果你做的是Array = foo ，那么你至less会碰到一个IRB的实现：
C:\Documents and Settings\a.grimm>irb irb(main):001:0> Array = nil (irb):1: warning: already initialized constant Array => nil C:/Ruby19/lib/ruby/site_ruby/1.9.1/rbreadline.rb:3177:in `rl_redisplay': undefined method `new' for nil:NilClass (NoMethodError) from C:/Ruby19/lib/ruby/site_ruby/1.9.1/rbreadline.rb:3873:in `readline_internal_setup' from C:/Ruby19/lib/ruby/site_ruby/1.9.1/rbreadline.rb:4704:in `readline_internal' from C:/Ruby19/lib/ruby/site_ruby/1.9.1/rbreadline.rb:4727:in `readline' from C:/Ruby19/lib/ruby/site_ruby/1.9.1/readline.rb:40:in `readline' from C:/Ruby19/lib/ruby/1.9.1/irb/input-method.rb:115:in `gets' from C:/Ruby19/lib/ruby/1.9.1/irb.rb:139:in `block (2 levels) in eval_input' from C:/Ruby19/lib/ruby/1.9.1/irb.rb:271:in `signal_status' from C:/Ruby19/lib/ruby/1.9.1/irb.rb:138:in `block in eval_input' from C:/Ruby19/lib/ruby/1.9.1/irb/ruby-lex.rb:189:in `call' from C:/Ruby19/lib/ruby/1.9.1/irb/ruby-lex.rb:189:in `buf_input' from C:/Ruby19/lib/ruby/1.9.1/irb/ruby-lex.rb:103:in `getc' from C:/Ruby19/lib/ruby/1.9.1/irb/slex.rb:205:in `match_io' from C:/Ruby19/lib/ruby/1.9.1/irb/slex.rb:75:in `match' from C:/Ruby19/lib/ruby/1.9.1/irb/ruby-lex.rb:287:in `token' from C:/Ruby19/lib/ruby/1.9.1/irb/ruby-lex.rb:263:in `lex' from C:/Ruby19/lib/ruby/1.9.1/irb/ruby-lex.rb:234:in `block (2 levels) in each_top_level_statement' from C:/Ruby19/lib/ruby/1.9.1/irb/ruby-lex.rb:230:in `loop' from C:/Ruby19/lib/ruby/1.9.1/irb/ruby-lex.rb:230:in `block in each_top_level_statement' from C:/Ruby19/lib/ruby/1.9.1/irb/ruby-lex.rb:229:in `catch' from C:/Ruby19/lib/ruby/1.9.1/irb/ruby-lex.rb:229:in `each_top_level_statement' from C:/Ruby19/lib/ruby/1.9.1/irb.rb:153:in `eval_input' from C:/Ruby19/lib/ruby/1.9.1/irb.rb:70:in `block in start' from C:/Ruby19/lib/ruby/1.9.1/irb.rb:69:in `catch' from C:/Ruby19/lib/ruby/1.9.1/irb.rb:69:in `start' from C:/Ruby19/bin/irb:12:in `<main>' C:\Documents and Settings\a.grimm>
那是因为Array是一个类。
arr = ["Jason", "Jason", "Teresa", "Judah", "Michelle", "Judah", "Judah", "Allison"] arr.uniq.inject({}) {|a, e| a.merge({e => arr.count(e)})}
经过的时间为0.028毫秒
有趣的是，stupidgeek的实施基准：
经过的时间0.041毫秒
和获胜的答案：
经过的时间为0.011毫秒
🙂
