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"}
~
原文：https://www.cnblogs.com/sidianok/p/13062669.html