Ruby入门——哈希表

哈希表（hash）是使用将某一任意对象作为键来对应其他对象的容器对象，相当于C++或Java中的映射。

例1

month_to_ordinal = {
"Jan" =>1, "Feb" =>2, "Mar" =>3, "Apr" =>4, "May" =>5, "Jun" =>6, "Jul" =>7, "Aug" =>8, "Sep" =>9, "Oct" =>10, "Nov" =>11, "Dec" =>12
}

p month_to_ordinal["Aug"]
p month_to_ordinal["Sep"]

#输出结果
#8
#9

创建哈希表

要生成哈希表只需将键和值得对应关系排列在花括号内就可以了。

例2

prefix = "yapoo-"
abbr = {
"CAT" => "Condensed-Abridged Tiger", "Yapomb" => prefix + "womb", "pilk" => prefix + "milk"
}

p abbr["CAT"]
p abbr["Yapomb"]
p abbr["pilk"]


#输出结果
#"Condensed-Abridged Tiger"
#"yapoo-womb"
#"yapoo-milk"

更简单的表示方法，使用符号“:”

例3

params = {rin: 5, kimiko: 7, Kayo:nil}
p params
p params[:rin]
p params[:kimiko]
p params[:Kayo]


#输出结果
#{:rin=>5, :kimiko=>7, :Kayo=>nil}
#5
#7
#nil

索引运算符表达式

例4

book_to_author = {
	"Ruby in Nutshell" => "Flanagan", 
	"Programming in Ruby" => "Thomas", 
	"AWDwr" => "Thomas"
}

p book_to_author["Programming in Ruby"]
p book_to_author["Programming in Perl"]
#更新已有的键值
p book_to_author["Ruby in Nutshell"] = ["Flanagan", "Matz"]
#添加新的键值
p book_to_author["The Ruby Way"] = "Fulton"


#输出结果
#"Thomas"
#nil
#["Flanagan", "Matz"]
#"Fulton"

哈希表的比较

hash对象之间，只有对象中所有对应的元素间的键和值都相等时才相等，但和顺序无关。

例5

hash1 = {"a" => 1, "b" =>2}
hash2 = {"a" => 1, "b" =>2}
p hash1 == hash2

#和顺序无关，相等
p hash1 == {"b" => 2, "a" =>1}
#值不一样，所以不相等
p hash1 == {"a" => 9, "b" =>2}
#键不一样，所以不相等
p hash1 == {"z" => 1, "b" =>2}
#有多余的内容，所以不相等
p hash1 == {"a" => 1, "b" =>2, "c" => 3}

#输出结果
#true
#true
#false
#false
#false

哈希表的其它方法

例6

book_to_author = {
	"Ruby in Nutshell" => "Flanagan", 
	"Programming in Ruby" => "Thomas", 
	"AWDwr" => "Thomas"
}

#size方法
p book_to_author.size

#用hash#each方法对哈希表的元素进行处理
book_to_author.each do |book, author|
	puts "#{book} by #{author}"
end

#hash#map会将代码块返回的值作为数组返回
p book_to_author.map{|book, author|  "#{book} by #{author}"}
#输出结果
#3
#Ruby in Nutshell by Flanagan
#Programming in Ruby by Thomas
#AWDwr by Thomas#["Ruby in Nutshell by Flanagan", "Programming in Ruby by Thomas", "AWDwr by Thomas"]

Enumerable模块

数组和哈希表之间除了map还有很多类似的方法，这是因为不论是数组还是哈希表，都同属于Enumerable这个模块。 Array和Hash都继承了Enumerable。

模块是为了让没有共同的继承的类拥有共同的实现而使用的方法。