一。给Hash添加默认值 :
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h = {1,2,3,4} #=> {1 => 2, 3 => 4}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.
default = 7
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h[1] #=> 2
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h[3] #=> 4
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h[4] #=> 7
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h[5] #=> 7
二。给Hash添加key-value对:
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h = {} #=> {}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.store(
"a",1) #=> 1
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h[
"a"] #=> 1
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.fetch(
"a") #=> 1
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h[
"b"] = 2 #=> 2
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h[
"b"] #=> 2
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
p h #=> {
"a"=>1,
"b"=>2}
store和[]= 方法是别名的关系, fetch和[]方法是别名的关系。
三。清除Hash的key-value对:
h = {:a => 1, :b => 2}
删除全部的k-v对,有两种方法:
给hash赋空值
用clear方法 (这种方法更快一点)
shift方法随机删除k-v对。
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h = {:a => 1, :b => 2, :c => 3}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.shift #=> [:a, 1]
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h #=> {:b=>2, :c=>3}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
a = h.shift #=> [:c, 3]
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
a #=> [:c, 3]
delete, delete_if, reject,reject! 方法删除指定的k-v对:
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h = {:a => 1, :b => 2}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.delete(:a) #=> 1
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h #=> {:b=>2}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h = {:a => 1, :b => 2} #=> {:a=>1, :b=>2}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.delete_if {|k,v| v != 3} #=> {}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h #=> {}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h = {:a => 1, :b => 2} #=> {:a=>1, :b=>2}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.delete_if {|k,v| v != 1} #=> {:a=>1}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h = {:a => 1, :b => 2} #=> {:a=>1, :b=>2}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.reject {|k,v| v!=2} #=> {:b=>2}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h #=> {:a=>1, :b=>2}
reject方法相当于dup.delete_if{}
四。颠倒Hash的k-v对。
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h = {:a => 1,:b => 1} #=> {:a=>1, :b=>1}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
x = h.invert #=> {1=>:b}
invert方法可以颠倒Hash的键-值,可是因为Hash键的唯一性,可能会发生上例那样的数据丢失!
五。 Hash的迭代:
有each, each_key, each_value ,each_pair(each方法的别名)
不举例了。
六。检测Hash中的key,value:
检测是否有key:
has_key?(include? 别名, 只能判断key! ) ,key?, member?
检测是否有value:
has_value? value?
七。将散列转换为数组:
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h = {:a => 1, :b => 2}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.to_a #=> [[:a, 1], [:b, 2]] 转换为一个二维数组。
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.keys #=> [:a, :b]
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.values #=> [1,2]
下面的方法有用点:
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h = {:a => 1, :b => '2', :c => 5}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.values_at(:a,:b) #=> [1, “2”] 根据指定的key返回对应values的数组
八。根据条件选择key-value对:
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.detect {|k,v| v ==
"2"} #=> [:b,
"2"]
detect和find是别名关系,是Enumerable模块里的方法,Hash类mixin这个模块,所以也可以用。select 方法,别名是find_all,可以返回多个匹配的k-v对:
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.select {|k,v| v.is_a?(Integer)} #=> [[:a, 1], [:c, 5]]
九。 Hash的排序:
可以直接用sort方法,不过会返回一个二维数组。
值得注意的是,当Hash的key是Symbol类型的时候,sort方法会出错。
十。 合并两个Hash:
使用merge方法,( merge!和update是别名关系 (thx Beck) ) 。
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h1 = {:a => 1, :b => 2} #=> {:a=>1, :b=>2}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h2 = {:b => 3, :d => 3} #=> {:d=>3, :b=>3}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h1.merge h2 #=> {:a=>1, :d=>3, :b=>3}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h2.merge h1 #=> {:a=>1, :d=>3, :b=>2}
注意看:b值的变化。
当然我们可以使用block来改变这一结局:
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h1.merge h2
do |k,old,
new|
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
old <
new ? old :
new![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
end
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
#=> {:a=>1, :d=>3, :b=>2}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h1.merge h2
do |k,old,
new|
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
p old
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
p
new![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
end
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
#=>2
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
#=>3
(当然我们可以使用rails里active_support实现的revert_merge来实现上述效果)。
十一。 数组转换为Hash:
当数组元素为偶数个数的时候:
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
arr = %w[a b c d] #=> [
"a",
"b",
"c",
"d"]
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h = Hash[*arr] #=> {
"a"=>
"b",
"c"=>
"d"}
此时数组必须为偶数个元素。
十二。 当Hash的key是动态变化的时候:
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
x = [1,2] #=> [1, 2]
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h = {x => 2} #=> {[1, 2]=>2}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h[x] #=> 2
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
x[0] = 5 #=> 5
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h[x] #=> nil
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h.rehash #=> {[5, 2]=>2}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h[x] #=> 2