ruby , each,map,collect,inject,reject,select,shuffle[n..m],flatten

ruby , each,map,collect,inject,reject,select,shuffle[n..m],flatten应用

一。把一字符串，根据其中的特殊字符 “.“ 分割成数组并去除空的字符串 ,我们得到一个数组 arr

arr = '.666.555.444.333.22.11.'.split('.').reject(&:blank?)

= 。each 的使用

数字：

2.0.0p0 :183 >   a = [1, 2, 3, 4, 5]
=> [1, 2, 3, 4, 5]
2.0.0p0 :184 > a.each {|number| puts number*2}
2
4
6
8
10
=> [1, 2, 3, 4, 5]
2.0.0p0 :185 >
字符：
2.0.0p0 :191 > lower_case = ["hi", "these", "are", "some", "words"]
=> ["hi", "these", "are", "some", "words"]
2.0.0p0 :192 > upper_case = []
=> []
2.0.0p0 :193 > lower_case.each do |word|
2.0.0p0 :194 >     upper_case << word.upcase
2.0.0p0 :195?>   end
=> ["hi", "these", "are", "some", "words"]
2.0.0p0 :196 > puts upper_case
HI
THESE
ARE
SOME
WORDS
=> nil
2.0.0p0 :197 >

三。collect的使用

2.0.0p0 :197 > lower_case = ["hi", "these", "are", "some", "words"]
=> ["hi", "these", "are", "some", "words"]
2.0.0p0 :198 > upper_case = lower_case.collect { |word| word.upcase }
=> ["HI", "THESE", "ARE", "SOME", "WORDS"]
2.0.0p0 :199 > puts upper_case.inspect
["HI", "THESE", "ARE", "SOME", "WORDS"]
=> nil
2.0.0p0 :200 >

四。map的使用

2.0.0p0 :200 > a = [ "a", "b", "c", "d" ]
=> ["a", "b", "c", "d"]
2.0.0p0 :201 > a.map { |x| x + "!" }
=> ["a!", "b!", "c!", "d!"]
2.0.0p0 :202 > a
=> ["a", "b", "c", "d"]
2.0.0p0 :203 >

五。reject的使用

2.0.0p0 :210 > (1..30).reject { |n| n % 2 == 0 }
=> [1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29]
2.0.0p0 :217 >   a = [1,2,3,4]
=> [1, 2, 3, 4]
2.0.0p0 :218 > a.reject {|n| n > 2}
=> [1, 2]
2.0.0p0 :219 >

六.select的使用

2.0.0p0 :224 >   a = [1,2,3,4]
=> [1, 2, 3, 4]
2.0.0p0 :225 > a.select {|n| n > 2}
=> [3, 4]
2.0.0p0 :226 >

七.inject的使用

enum.inject(init_value) {|memo,obj|  block}
enum.inject{ |memo,obj| block }

2.0.0p0 :226 > [1, 2, 3, 4].inject { |result, element| result + element }
=> 10

2.0.0p0 :227 > hash = [[:first_name, 'Shane'], [:last_name, 'Harvie']].inject({}) do |result, element|
2.0.0p0 :228 >       result[element.first] = element.last
2.0.0p0 :229?>     result
2.0.0p0 :230?>   end
=> {:first_name=>"Shane", :last_name=>"Harvie"}
2.0.0p0 :231 >

把array转换成hash表。有也第一个例子的基础，这个例子应该很容易看得懂。

[1, 2, 3, 4].inject(0) { |result, element| result + element } # => 10

inject带有一个参数和block。block中的两个参数是有含义的。第一个参数reslut在inject第一次执行block时把inject带的参数付值给它，element就是数组中的元素，该例中inject一共执行4次block，每次执行block完后，最后语句的结果再付值给result，如此循环，直到遍历数组中所有元素。我们深入这个例子看每一步执行的结果。

因为数组有4个元素，所以要执行4次block操作：

第一次操作：result=0，既等于inject带的参数；element=1，既第一个元素；执行block后result + element =1，再把这个结果付值给result，所以在执行完第一次block后，result = 1。

第二次操作:result=1，既上次运行block后的最后一条语句的结果；element=2，既第二个元素；执行block后付值result＝3。

如此类推，直到最后一次执行完block，生产的值为10。就是inject的返回值了。

八。shuffle[n..m]

('a'..'z').to_a.shuffle[0..7].join

一个相关的网站：http://blog.jayfields.com/2008/03/ruby-inject.html

九. flatten

2.0.0p247 :002 > [1,2,3,4,5,[6,7,8],[9,1,[1,2]]].flatten
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 1, 2]
2.0.0p247 :003 >