Ruby 札记 - Ruby 集合家族之数组（Array）

学习 Ruby 集合我觉得最好的方式是打开 irb --simple-prompt 命令，跟着例子学习。试着借助 Tab 补全加以思考?。

创建数组

和其他动态语言创建相似。

>> a = [1, 2, 3]
=> [1, 2, 3]
>> a.class
=> Array
>> a.length
=> 3
>> a.size
=> 3
>> a[2]
=> 3
>> a << 4
=> [1, 2, 3, 4]
>> a
=> [1, 2, 3, 4]
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其中类型不必相同，可以同时是 String 、Number 等

?> a = [1, "Grac Kanil", [2, 3]]
=> [1, "Grac Kanil", [2, 3]]
>>
?> a << true
=> [1, "Grac Kanil", [2, 3], true]
>> a << 3.14
=> [1, "Grac Kanil", [2, 3], true, 3.14]
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一切皆对象，当然数组跑不了这个范畴

?> a = Array.new([1, "Hello", 2])
=> [1, "Hello", 2]
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数组创建可以传参数，提前申请控件，但是数组是动态的，如果传入数组，会创建包含 nil 的数组。nil 也是一个对象，所以再追加，会在 nil 之后添加。当然可以快速传入默认值，占位数组。

?> a = Array.new(3)
=> [nil, nil, nil]
>>
?> a = Array.new(3, 1)
=> [1, 1, 1]
>>
?>
?> a = Array.new(3)
=> [nil, nil, nil]
>>
?> a << 3
=> [nil, nil, nil, 3]
?> a.size
=> 4
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切割字符串为数组

• scan 方法

>> s = "This is a test string."
=> "This is a test string."
>> s.scan(/\w/).join(",")
=> "T,h,i,s,i,s,a,t,e,s,t,s,t,r,i,n,g"
?> s.scan(/\b\w*\b/)
=> ["This", "", "is", "", "a", "", "test", "", "string", ""]
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• split 方法

>> s = "This is a test string."
=> "This is a test string."
?> s.split(" ")
=> ["This", "is", "a", "test", "string."]
>> s.split(" ").inspect
=> "[\"This\", \"is\", \"a\", \"test\", \"string.\"]"

?> s.split(/\s+/)
=> ["This", "is", "a", "test", "string."]
>> s.split(/\s+/).inspect
=> "[\"This\", \"is\", \"a\", \"test\", \"string.\"]"
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• % 来实现的语法捷径

?> est = "est"
=> "est"
>> %W{This is a t#{est} string.}
=> ["This", "is", "a", "test", "string."]
>>
?> %w{This is a t#{est} string.}
=> ["This", "is", "a", "t\#{est}", "string."]
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数组越界问题

很多语言访问不存在的索引，会抛出数组越界异常，但 ruby 中不会，会返回 nil 哦

?> a = []
=> []
>> a[4]
=> nil
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cool!? 以上是读，如果写入呢？

?> a
=> []
>> a[3] = "Grac"
=> "Grac"
>> a
=> [nil, nil, nil, "Grac"]
>> a[7] = "Kanil"
=> "Kanil"
>>
?> a
=> [nil, nil, nil, "Grac", nil, nil, nil, "Kanil"]
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so cool! 在很多语言中，如果你的索引值小于 0 呢，又会怎样？

?> a = [1, 2, 3]
=> [1, 2, 3]
>>
?> a[-1]
=> 3
>>
?> a[-4]
=> nil
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wonderful!

数组分类

表示数组前两个元素的多种表示方法

?> strings = %w{a b c d e f g}
=> ["a", "b", "c", "d", "e", "f", "g"]
>>
?> strings[0..1]
=> ["a", "b"]
>> strings[0...1]
=> ["a"]
>> strings[0...2]
=> ["a", "b"]
>> strings[0,2]
=> ["a", "b"]
>> strings[-7,2]
=> ["a", "b"]
>> strings[-7..-6]
=> ["a", "b"]
>> strings[-7...2]
=> ["a", "b"]
>> strings[-7..1]
=> ["a", "b"]
>> strings[0..-6]
=> ["a", "b"]
>> strings[0...-5]
=> ["a", "b"]
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进阶思考

>> (0..1).class
=> Range
?> strings.[](0..1)
=> ["a", "b"]
>> strings.[](Range.new(0,1))
=> ["a", "b"]
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有趣的 numerouno

➜  ~ gem install numerouno
Fetching: numerouno-0.2.0.gem (100%)
Successfully installed numerouno-0.2.0
Parsing documentation for numerouno-0.2.0
Installing ri documentation for numerouno-0.2.0
Done installing documentation for numerouno after 0 seconds
1 gem installed
➜  ~ irb --simple-prompt

?> require 'numerouno'
=> true
>>
?> "sixty one".as_number
=> 61

# 为数组添加英文索引
?> class EnglishArray < Array
>>   def [](idx)
>>     if String === idx
>>       self.at(idx.as_number)
>>     end
>>   end
>> end
=> :[]
>>
?> array = EnglishArray.new([1, 2, 3, 4])
=> [1, 2, 3, 4]
>>
?> array["one"]
=> 2
>> array["three"]
=> 4
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Ruby 数组的万能结构

• 栈 可以将数组作为栈。其功能和 Python list 相似，使用 pop 和 push 方法。

?> a = []
=> []
>> a.push(3)
=> [3]
>> a.push("Grac")
=> [3, "Grac"]
>>
?> a.push("Kanil")
=> [3, "Grac", "Kanil"]
>>
?>
?> a.pop
=> "Kanil"
>> a.pop
=> "Grac"
>> a.pop
=> 3
>> a
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• 队列 队列，即先进先出

?> a = []
=> []
>> a.push(1)
=> [1]
>> a.push(2)
=> [1, 2]
>> a.push(3)
=> [1, 2, 3]
>> a.shift
=> 1
>> a.shift
=> 2
>> a.shift
=> 3
>> a
=> []
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还可以使用 unshift 队首加入新元素

?> a = []
=> []
>> a.push(1)
=> [1]
>> a.unshift(2)
=> [2, 1]
>> a.unshift(3)
=> [3, 2, 1]
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使用 delete 删除任意位置元素

?> a = [1, 2, 3]
=> [1, 2, 3]
>> a.delete(2)
=> 2
>> a
=> [1, 3]
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• 集合

?> [1, 2, 3] + [4, 5, 6]
=> [1, 2, 3, 4, 5, 6]

?> [1, 2, 3] + [2, 3]
=> [1, 2, 3, 2, 3]

>> [1, 2, 3].concat([4, 5, 6])
=> [1, 2, 3, 4, 5, 6]

>> ["a", 1, 2, 3, "b"] - ["a", "b"]
=> [1, 2, 3]

>> [1, 2, 4] & [1, 2, 3]
=> [1, 2]

>> [1, 2, 4] | [1, 2, 3]
=> [1, 2, 4, 3]
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Ruby 数组常用方法

• 检查数组是否为空

>> a = []
=> []
>> a.empty?
=> true
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• 移动元素

# 转置
?> [1, 2, 4].reverse
=> [4, 2, 1]

# 向左移动一
?> [1, 2, 4].rotate
=> [2, 4, 1]

# 向右移动一
?> [1, 2, 4].rotate(-1)
=> [4, 1, 2]
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• 安全提示

?> a = [1, 2, 3]
=> [1, 2, 3]
>> a.freeze
=> [1, 2, 3]
>> a << 4
RuntimeError: can't modify frozen Array
	from (irb):85
	from /Users/gekang/.rvm/rubies/ruby-2.2.4/bin/irb:11:in `<main>'
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• 数组的 join 方法，将元素都链接为字符串

?> a = [1, 2, "Grac", "Kanil"]
=> [1, 2, "Grac", "Kanil"]
>>
?> a.join
=> "12GracKanil"
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当然，可以传入参数

?> a.join(",")
=> "1,2,Grac,Kanil"
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• 删除嵌套

?> [1, [2, 3], [4, ["a", nil]]].flatten
=> [1, 2, 3, 4, "a", nil]
>>
?> [1, [2, 3], [4, ["a", nil]]].flatten(1)
=> [1, 2, 3, 4, ["a", nil]]
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• 删除副本

?> [4, 1, 2, 3, 1, 4].uniq
=> [4, 1, 2, 3]
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• 检查是否包含某元素

?> a = [1, "a", 2]
=> [1, "a", 2]
>> a.include? "a"
=> true
>> a.include? 1
=> true
>> a.include?(1)
=> true
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• 分割数组

?> a = [1, 2, 3, 4, 5, 6]
=> [1, 2, 3, 4, 5, 6]
>> a.first
=> 1
>> a.last
=> 6
>> a.first(3)
=> [1, 2, 3]
>> a.last(4)
=> [3, 4, 5, 6]
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• 统计数组中某元素的个数

?> a = [4, 1, 2, 3, 1, 4]
=> [4, 1, 2, 3, 1, 4]
>> a.count 4
=> 2
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• 查询数组所有方法

?> Array.methods
=> [:[], :try_convert, :allocate, :new, :superclass, :freeze, :===, :==, :<=>, :<, :<=, :>, :>=, :to_s, 
:inspect, :included_modules, :include?, :name, :ancestors, :instance_methods, :public_instance_methods, :protected_instance_methods, :private_instance_methods, :constants, :const_get, :const_set, 
:const_defined?, :const_missing, :class_variables, :remove_class_variable, :class_variable_get, 
:class_variable_set, :class_variable_defined?, :public_constant, :private_constant, :singleton_class?, 
:include, :prepend, :module_exec, :class_exec, :module_eval, :class_eval, :method_defined?, 
:public_method_defined?, :private_method_defined?, :protected_method_defined?, :public_class_method, :private_class_method, :autoload, :autoload?, :instance_method, :public_instance_method, :nil?, :=~, 
:!~, :eql?, :hash, :class, :singleton_class, :clone, :dup, :itself, :taint, :tainted?, :untaint, 
:untrust, :untrusted?, :trust, :frozen?, :methods, :singleton_methods, :protected_methods, 
:private_methods, :public_methods, :instance_variables, :instance_variable_get, :instance_variable_set, :instance_variable_defined?, :remove_instance_variable, :instance_of?, :kind_of?, :is_a?, :tap, 
:send, :public_send, :respond_to?, :extend, :display, :method, :public_method, :singleton_method, :define_singleton_method, :object_id, :to_enum, :enum_for, :equal?, :!, :!=, :instance_eval, 
:instance_exec, :__send__, :__id__]
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迭代

迭代可以说是 Ruby 的一大亮点，我觉得 Objective-C 中的迭代就很少使用，比较笨重，更多的会想到写一个 for 循环，然而，Ruby 并不会，优雅的迭代使用起来比较顺手。

each

Ruby 中迭代的核心应该就是 each 方法了

?> a = ["This", "is", "a", "test", "string"]
=> ["This", "is", "a", "test", "string"]
>>
?> a.each {|s| puts s.cap} # Tab 键可以联想
s.capitalize   s.capitalize!  s.captures

?> a.each { |s| puts s.capitalize }
This
Is
A
Test
String
=> ["This", "is", "a", "test", "string"]
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还有 reverse_each 反向迭代

?> a = ["This", "is", "a", "test", "string"]
=> ["This", "is", "a", "test", "string"]
>> a.reverse_each { |s| puts s.up }
s.upcase   s.upcase!  s.update   s.upto
>> a.reverse_each { |s| puts s.upcase }
STRING
TEST
A
IS
THIS
=> ["This", "is", "a", "test", "string"]
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如果你需要索引，当然也给你准备好了当前处理的索引 each_with_index

>> a = ["This", "is", "a", "test", "string"]
=> ["This", "is", "a", "test", "string"]
>> a.each_with_index { |s, index| puts "#{index} is #{s}" }
0 is This
1 is is
2 is a
3 is test
4 is string
=> ["This", "is", "a", "test", "string"]
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如果你需要迭代数组中某一部分，可以使用分割数组

?> a = ["This", "is", "a", "test", "string"]
=> ["This", "is", "a", "test", "string"]
>> a[0..2]
=> ["This", "is", "a"]
>> a[0..2].each {|s| puts s}
This
is
a
=> ["This", "is", "a"]
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也可以使用 Range 来实现

?> a = ["This", "is", "a", "test", "string"]
=> ["This", "is", "a", "test", "string"]
>>
?> (0..2).each {|i| puts a[i]}
This
is
a
=> 0..2
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map 或 collect

>> a = [1, 2, 3]
=> [1, 2, 3]
>> a.map { |i| i + 1 }
=> [2, 3, 4]
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如果只是让每一个元素调用方法，不关心每个元素的值时，可以使用快捷写法

>> a = [1, 2, 3]
=> [1, 2, 3]
>> a.map(&:to_f)
=> [1.0, 2.0, 3.0]
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#map 不改变原来的数组，而是会生成新的数组，如果需要修改原数组，需要使用 #map! 方法

>> a = [1, 2, 3]
=> [1, 2, 3]
>> a.map(&:to_f)
=> [1.0, 2.0, 3.0]
>>
?> a
=> [1, 2, 3]
>> a.map!(&:to_f)
=> [1.0, 2.0, 3.0]
>> a
=> [1.0, 2.0, 3.0]
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#map 和 #collect 相同，可以互换使用

?> a = [1, 2, 3]
=> [1, 2, 3]
>> a.map(&:to_f)
=> [1.0, 2.0, 3.0]
>> a.collect(&:to_f)
=> [1.0, 2.0, 3.0]
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