《Rubu基础教程第五版》第十五章笔记 散列值

操作 散列 哈希 ，字典

散列的创建

用字面量进行创建,{}

{键 => 值}或 {键: 值}

使用Hash.new

irb(main):004:0> h1 = Hash.new
=> {}
irb(main):005:0> h2 = Hash.new("ha")
=> {}
irb(main):006:0> h1["not key"]
=> nil
irb(main):007:0> h2["not key"]
=> "ha"
irb(main):008:0> 

 Hash.new可以穿件没有key情况下的返回值

散列的键可以使用各种对象，不过一般建议使用下面的对象作为散列的键

字符串，数值，符号，日期

 

值的获取与设定

=> {}
irb(main):010:0> h["R"] = 
irb(main):011:0* "Ruby"
=> "Ruby"
irb(main):012:0> p h["R"]
"Ruby"
=> "Ruby"
irb(main):013:0> h
=> {"R"=>"Ruby"}
irb(main):014:0> h.store("P", "Python")
=> "Python"
irb(main):015:0> h["P"]
=> "Python"
irb(main):016:0> h.fetch("p")
Traceback (most recent call last):
        5: from /usr/bin/irb:23:in `<main>'
        4: from /usr/bin/irb:23:in `load'
        3: from /Library/Ruby/Gems/2.6.0/gems/irb-1.0.0/exe/irb:11:in `<top (required)>'
        2: from (irb):16
        1: from (irb):16:in `fetch'
KeyError (key not found: "p")
Did you mean?  "P"
irb(main):017:0> h.fetch("P")
=> "Python"
irb(main):018:0> h.fetch("la","moyou")
=> "moyou"
irb(main):019:0> h.fetch("la"){ " meiyou" }
=> " meiyou"
irb(main):020:0> h.fetch("la", String.new)
=> ""
irb(main):021:0> 

 这里主要是一个fetch，取不到值的情况下，可以取后面的值。

 

一次性获取所有的键、值

键 .keys 值.values [键_值] .to_a

irb(main):023:0> h = {"a"=>"b", "c"=>"d"}
=> {"a"=>"b", "c"=>"d"}
irb(main):024:0> h.keys
=> ["a", "c"]
irb(main):025:0> h.values
=> ["b", "d"]
irb(main):026:0> h.to_a
=> [["a", "b"], ["c", "d"]]
irb(main):027:0> h.values.clear
=> []
irb(main):028:0> h
=> {"a"=>"b", "c"=>"d"}
irb(main):029:0> 

 

散列的默认值

.new的值就是散列的默认值，默认是nil

 

指定生成默认值的块

irb(main):033:0> h = Hash.new do |hash, key|
irb(main):034:1* hash[key] = key.upcase
irb(main):035:1> end
=> {}
irb(main):036:0> h
=> {}
irb(main):037:0> h["a"] = "aa"
=> "aa"
irb(main):038:0> h["b"]
=> "B"
irb(main):039:0> h["cc"]
=> "CC"
irb(main):040:0> 

 do 方式，第一参数是hash，第二参数是key

 

用fetch取值，不收默认值的影响

 

查看指定对象是否为散列的键或值

查看键

h.key?(key)

h.has_key?(key)

h.include?(key)

h.member?(key)

上面4个方法效果一样的

irb(main):044:0> h
=> {"a"=>"aa", "b"=>"B", "cc"=>"CC"}
irb(main):045:0> h.key?("a")
=> true
irb(main):046:0> h.has_key?("a")
=> true
irb(main):048:0> h.include?("a")
=> true
irb(main):049:0> h.member?("a")
=> true
irb(main):050:0> 

 查看value在不在用

.value?与.has_value?

 

查看散列的大小

size length

irb(main):053:0> h
=> {"a"=>"aa", "b"=>"B", "cc"=>"CC"}
irb(main):054:0> h.size
=> 3
irb(main):055:0> h.length
=> 3
irb(main):056:0> 

 .empty?查看是否为空

 

删除键值

h.delete(key)

irb(main):063:0> h
=> {"b"=>"B", "cc"=>"CC", "a"=>"aa"}
irb(main):064:0> h.delete("a")
=> "aa"
irb(main):065:0> h
=> {"b"=>"B", "cc"=>"CC"}
irb(main):066:0> 

 

delete_if{|key, value| ...}

reject!{|key,value| ...}

irb(main):066:0> h
=> {"b"=>"B", "cc"=>"CC"}
irb(main):067:0> h.delete_if{|k,v| k == "b"}
=> {"cc"=>"CC"}
irb(main):068:0> h
=> {"cc"=>"CC"}
irb(main):069:0> h.reject!{|k,v| k == "cc"}
=> {}
irb(main):070:0> h
=> {}
irb(main):071:0> 

 reject!,delete_if如果都有符合的条件，那返回的都是排除条件后剩余的字典，如果没有符合的条件，delete_if返回剩余的字典，reject!返回nil

irb(main):072:0> h = {a:"a", b:"b", c:"c"}
=> {:a=>"a", :b=>"b", :c=>"c"}
irb(main):073:0> h.delete_if{|k,v| k == :a}
=> {:b=>"b", :c=>"c"}
irb(main):074:0> h.reject!{|k,v| k == :b}
=> {:c=>"c"}
irb(main):075:0> h
=> {:c=>"c"}
irb(main):076:0> h.reject!{|k,v| k == :d}
=> nil
irb(main):077:0> h.delete_if{|k,v| k == :d}
=> {:c=>"c"}
irb(main):078:0> 

 

初始化散列

.clear

 

合并两个散列

用了merge的方法

irb(main):084:0> b = {'1':2}
=> {:"1"=>2}
irb(main):085:0> a
=> {[12, 3]=>12}
irb(main):086:0> b
=> {:"1"=>2}
irb(main):087:0> a.merge(b)
=> {[12, 3]=>12, :"1"=>2}
irb(main):088:0> a
=> {[12, 3]=>12}
irb(main):089:0> b
=> {:"1"=>2}
irb(main):090:0> c= a.merge(b)
=> {[12, 3]=>12, :"1"=>2}
irb(main):091:0> c
=> {[12, 3]=>12, :"1"=>2}
irb(main):092:0> 

 这个是产生一个新值，自身不发生变化

 

写一个计算单词数量的脚本

#! /usr/bin/env ruby

count = Hash.new(0)   # 字典默认值是0

File.open(ARGV[0]) do |file|
  file.each_line do |line|
    words = line.split
    words.each do |word|
      count[word] += 1
   end
  end
end



# 输出结果进行排序
count.sort do |a, b|
  a[1] <=> b[1]
end.each do |key ,value|
  print "#{key}: #{value}\n"
end

 整个脚本最后意思的就是排序那个部分的sort写法，另外的逻辑也比较清除简单

 

联系题

1输出表达式如下

wday = {sunday: "星期天", monday: "星期一", tuesday: "星期二", wendesday: "星期三",
  thursday: "星期四", friday: "星期五", saturday: "星期六"}

p wday.keys.size

wday.each {|k, v| 
 puts(k.to_s+"是"+v+"。")
}
~        

 

定义一个方法

def str2hash(str)
  hash = {}
  str.each_line do |line|
    array = line.chomp.split
    (array.size/2).times do |i|
       hash[array[i]] = array[i+1]
    end
  end
  hash
end


p str2hash("bule 蓝色 white 白色 \nred 红色")   # {"bule"=>"蓝色", "蓝色"=>"white", "red"=>"红色"}
~