From: Robert Klemme <shortcutter@...>
Date: 2012-01-13T23:18:12+09:00
Subject: Re: negative grep

On Thu, Jan 12, 2012 at 10:22 PM, Peter Vandenabeele
<peter@vandenabeele.com> wrote:
> On Thu, Jan 12, 2012 at 9:36 PM, Chad Perrin <code@apotheon.net> wrote:
>
>> On Fri, Jan 13, 2012 at 05:26:59AM +0900, Matt Lawrence wrote:
>> > On Fri, 13 Jan 2012, Robert Klemme wrote:
>> >
>> > >I'd use #select with inverted condition or #reject
>> > >
>> > >irb(main):005:0> a.select {|s| /0/ !~ s}
>> >
>> > That worked perfectly, thank you.  A a sysadmin, I use "grep -v"
>> > quite a bit and I was hoping that the grep method in Ruby had a
>> > similar capability.  Using select is a bit wordier and not quite as
>> > apparent as to what is going on, but it works very well.
>>
>> Do you object to reject?
>>
>
> Well, a 'v' option, equivalent to the UNIX grep seems quite straightforward
> to conceive?
>
> peterv@ASUS:~$ ruby -v
> ruby 1.9.3p0 (2011-10-30 revision 33570) [i686-linux]
> peterv@ASUS:~$ echo -e "abc\ndef\nghi" | grep abc
> abc
> peterv@ASUS:~$ echo -e "abc\ndef\nghi" | grep -v abc
> def
> ghi
> peterv@ASUS:~$ ruby -e 'puts %w{ abc def ghi}.grep(/abc/)'
> abc
> peterv@ASUS:~$ ruby -e 'puts %w{ abc def ghi}.grep(/abc/v)'
> -e:1: unknown regexp option - v
>
> Having "def" and "ghi" as a result here would be nice :-)

Pretty easy to do:

module Enumerable
  def grep_v(cond)
    select {|x| not cond === x}
  end
end

irb(main):006:0> a=10.times.map &:to_s
=> ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9"]
irb(main):007:0> a.grep /0/
=> ["0"]
irb(main):008:0> a.grep_v /0/
=> ["1", "2", "3", "4", "5", "6", "7", "8", "9"]

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/