Ruby,从字符串中删除最后N个字符？

Question

n从字符串中删除最后一个字符的首选方法是什么？

Answer 1

irb> 'now is the time'[0...-4]
=> "now is the "

Answer 2

如果要删除的字符始终是相同的字符,请考虑chomp:

'abc123'.chomp('123')    # => "abc"

优点chomp是:不计数,代码更清楚地传达它正在做的事情.

如果没有参数,则chomp删除DOS或Unix行结尾(如果存在):

"abc\n".chomp      # => "abc"
"abc\r\n".chomp    # => "abc"

从评论来看,存在使用速度#chomp与使用范围的问题.以下是比较两者的基准:

require 'benchmark'

S = 'asdfghjkl'
SL = S.length
T = 10_000
A = 1_000.times.map { |n| "#{n}#{S}" }

GC.disable

Benchmark.bmbm do |x|
  x.report('chomp') { T.times { A.each { |s| s.chomp(S) } } }
  x.report('range') { T.times { A.each { |s| s[0...-SL] } } }
end

基准测试结果(使用CRuby 2.13p242):

Rehearsal -----------------------------------------
chomp   1.540000   0.040000   1.580000 (  1.587908)
range   1.810000   0.200000   2.010000 (  2.011846)
-------------------------------- total: 3.590000sec

            user     system      total        real
chomp   1.550000   0.070000   1.620000 (  1.610362)
range   1.970000   0.170000   2.140000 (  2.146682)

所以chomp比使用范围更快,大约22%.

Answer 3

str = str[0...-n]

Answer 4

我建议chop.我认为它已在其中一条评论中提及,但没有链接或解释,所以这就是为什么我认为它更好:

它只是从字符串中删除最后一个字符,您不必为此指定任何值.

如果您需要删除多个角色,那么这chomp是您最好的选择.这就是ruby docs所说的chop:

返回删除了最后一个字符的新String.如果字符串以\ r \n结尾,则删除两个字符.将chop应用于空字符串会返回一个空字符串.String#chomp通常是一种更安全的替代方法,因为它不会在记录分隔符中结束时保持字符串不变.

虽然这主要用于删除分隔符,例如\r\n我用它来删除简单字符串中的最后一个字符,例如s使单词成为单数.

Answer 5

name = "my text"
x.times do name.chop! end

在控制台中:

>name = "Nabucodonosor"
 => "Nabucodonosor" 
> 7.times do name.chop! end
 => 7 
> name
 => "Nabuco" 

Answer 6

删除最后一个n字符与保留第一个length - n字符相同.

Active Support包含String#first和String#last方法,它们提供了一种方便的方法来保留或删除第一个/最后一个n字符:

require 'active_support/core_ext/string/access'

"foobarbaz".first(3)  # => "foo"
"foobarbaz".first(-3) # => "foobar"
"foobarbaz".last(3)   # => "baz"
"foobarbaz".last(-3)  # => "barbaz"

Answer 7

Ruby 2.5+

As of Ruby 2.5 you can use delete_suffix or delete_suffix! to achieve this in a fast and readable manner.

The docs on the methods are here.

If you know what the suffix is, this is idiomatic (and I'd argue, even more readable than other answers here):

'abc123'.delete_suffix('123')     # => "abc"
'abc123'.delete_suffix!('123')    # => "abc"

It's even significantly faster (almost 40% with the bang method) than the top answer. Here's the result of the same benchmark:

                     user     system      total        real
chomp            0.949823   0.001025   0.950848 (  0.951941)
range            1.874237   0.001472   1.875709 (  1.876820)
delete_suffix    0.721699   0.000945   0.722644 (  0.723410)
delete_suffix!   0.650042   0.000714   0.650756 (  0.651332)

I hope this is useful - note the method doesn't currently accept a regex so if you don't know the suffix it's not viable for the time being. However, as the accepted answer (update: at the time of writing) dictates the same, I thought this might be useful to some people.

Answer 8

如果您使用rails,请尝试:

"my_string".last(2) # => "ng"

[EDITED]

要获得没有最后2个字符的字符串:

n = "my_string".size
"my_string"[0..n-3] # => "my_stri"

注意:最后一个字符串char是n-1.因此,要删除最后2个,我们使用n-3.

Answer 9

查看slice()方法：

http://ruby-doc.org/core-2.5.0/String.html#method-i-slice