Ruby on Rails字符串处理(2)
Ruby字符串处理函数
1.返回字符串的长度
str.length => integer
2.判断字符串中是否包含另一个串
str.include? other_str #true or false
"hello".include? "lo" #=> true
"hello".include? "ol" #=> false
"hello".include? ?h #=> true
3.字符串插入:
str.insert(index, other_str) #str
"abcd".insert(0, 'X') #=> "Xabcd"
"abcd".insert(3, 'X') #=> "abcXd"
"abcd".insert(4, 'X') #=> "abcdX"
"abcd".insert(-3, 'X') #=> "abXcd"
"abcd".insert(-1, 'X') #=> "abcdX"
4.字符串分隔,默认分隔符为空格
str.split(pattern=$;, [limit]) # anArray
" now's the time".split #=> ["now's", "the", "time"]
"1, 2.34,56, 7".split(%r{,\s*}) #=> ["1", "2.34", "56", "7"]
"hello".split(//) #=> ["h", "e", "l", "l", "o"]
"hello".split(//, 3) #=> ["h", "e", "llo"]
"hi mom".split(%r{\s*}) #=> ["h", "i", "m", "o", "m"]
"mellow yellow".split("ello") #=> ["m", "w y", "w"]
"1,2,,3,4,,".split(',') #=> ["1", "2", "", "3", "4"]
"1,2,,3,4,,".split(',', 4) #=> ["1", "2", "", "3,4,,"]
也可以指定切分符：
"apples, pears, and peaches".split(", ") # ["apples", "pears", "and peaches"]
"lions and tigers and bears".split(/ and /) # ["lions", "tigers", "bears"]
splite方法的第二个参数用来限制切分的返回结果个数，具体效果规则如下：
1.如果省略这个参数,则切分结果中末尾为null的结果将被压缩掉
2.如果是正数，则结果按照指定的限制数量进行切分，尾部的null结果也将会保留做为结果
3.如果是负数，则切分结果数量无限制，并且保留尾部的null结果。
例如：
str = "alpha,beta,gamma,,"
list1 = str.split(",") # ["alpha","beta","gamma"]
list2 = str.split(",",2) # ["alpha", "beta,gamma,,"]
list3 = str.split(",",4) # ["alpha", "beta", "gamma", ","]
list4 = str.split(",",8) # ["alpha", "beta", "gamma", "", ""]
list5 = str.split(",",-1) # ["alpha", "beta", "gamma", "", ""]
5、格式化字符串
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Ruby的字符串格式话沿用了C的格式，在C中可用于sprintf或printf的格式话字符在Ruby中同样适用：
name = "Bob"
age = 28
str = sprintf("Hi, %s... I see you're %d years old.", name, age)
String类有个%方法，可以方面的做格式化的工作，它接受任何类型的单个值或一个数组：
str = "%-20s %3d" % [name,age]
上面这个和下面这个式子是等效的
str = sprintf("%-20s %3d", name, age)
我们还可以使用ljust,rjust,center方法来格式化我们的字符串：
str = "Moby-Dick"
s1 = str.ljust(13) #"Moby-Dick "
s2 = str.center(13) #" Moby-Dick "
s3 = str.rjust(13) #" Moby-Dick"
6、控制字符串的大小写
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Ruby的String类提供了一组丰富的方法来控制大小写：
s = "Hello,World"
s1 = s.downcase #"hello,world"
s2 = s.upcase #"HELLO,WORLD"
capitalize方法把字符串第一个字符变大写，其余都是小写：
s3 = s.capitalize #"Hello,world"
swapcase则是把字符串中的每个字符的大小写转换一下(原来大写的都小写，反之亦然)：
s = "HELLO,world"
s1 = s.swapcase #"hello,WORLD"
这些方法都有相应的in-place方法
(upcase!,downcase!,capitalize!,swapcase!)
虽然，Ruby没有提供内置的判断字符是否是大小写的方法，但是，这不是问题，我们可以通过正则表达式来完成这一点:
if string =~ /[a-z]/
puts "string contains lowercase charcters"
end
if string =~ /[A-Z]/
puts "string contains uppercase charcters"
end
if string =~ /[A-Z]/ and string =~ /a-z/
puts "string contains mixed case"
end
if string[0..0] =~ /[A-Z]/
puts "string starts with a capital letter"
end
字符串的子串
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Ruby提供了多种访问操作字符串子串的方式，我们可以来看一下：
1.如果给出一组数字，则第一个数字代表取字符串的偏移位置，第二个数字表示
取的长度：
str = "Humpty Dumpty"
sub1 = str[7,4] # "Dump"
sub2 = str[7,99] # "Dumpty" (超过的长度按实际长度来取)
sub3 = str[10,-4] # nil (长度为负数了)
记住，上面的形式，很多从别的语言转过来的ruby初学者会认为给出的两个数字是子串的开始和结束位置的偏移，这是错误的，务必记住。
给出的偏移是负数也是可以的,这样，位置将从字符串末尾开始计算：
str1 = "Alice"
sub1 = str1[-3,3] # "ice"
str2 = "Through the Looking-Glass"
sub3 = str2[-13,4] # "Look"
我们也可以给出一个Range来取子串：
str = "Winston Churchill"
sub1 = str[8..13] # "Church"
sub2 = str[-4..-1] # "hill"
sub3 = str[-1..-4] # nil
sub4 = str[25..30] # nil
强大的是，正则表达式在这个时候也充分发挥着作用：
str = "Alistair Cooke"
sub1 = str[/l..t/] # "list"
sub2 = str[/s.*r/] # "stair"
sub3 = str[/foo/] # nil
如果给出的是一个字符串，则如果目标字符串中含有这个给出的字符串，则返回这个给出的字符串，否则返回nil：
str = "theater"
sub1 = str["heat"] # "heat"
sub2 = str["eat"] # "eat"
sub3 = str["ate"] # "ate"
sub4 = str["beat"] # nil
sub5 = str["cheat"] # nil
如果给出的是一个数字，则返回的是该数字对应索引处字符的ASCII码：
str = "Aaron Burr"
ch1 = str[0] # 65
ch1 = str[1] # 97
ch3 = str[99] # nil
同样，我们不仅可以通过上面的方式访问子串，还可以来向字符串设置内容：
str1 = "Humpty Dumpty"
str1[7,4] = "Moriar" # "Humpty Moriarty"
str2 = "Alice"
str2[-3,3] = "exandra" # "Alexandra"
str3 = "Through the Looking-Glass"
str3[-13,13] = "Mirror" # "Through the Mirror"
str4 = "Winston Churchill"
str4[8..13] = "H" # "Winston Hill"
str5 = "Alistair Cooke"
str5[/e$/] ="ie Monster" # "Alistair Cookie Monster"
str6 = "theater"
str6["er"] = "re" # "theatre"
str7 = "Aaron Burr"
str7[0] = 66 # "Baron Burr"