ruby 哈希常用方法
2015-09-12 09:58
375 查看
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}
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.mergeh2 #=>
{:a=>1, :d=>3, :b=>3}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h2.mergeh1 #=>
{: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.mergeh2 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)
pold
![](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 cd] #=>
["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
![](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}
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.mergeh2 #=>
{:a=>1, :d=>3, :b=>3}
![](http://blackanger.blog.51cto.com/images/editer/InBlock.gif)
h2.mergeh1 #=>
{: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.mergeh2 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)
pold
![](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 cd] #=>
["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
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