From: Robert Klemme <shortcutter@...>
Date: 2007-07-20T16:42:16+09:00
Subject: Re: Is there a replacement for sub?

2007/7/20, Michael W. Ryder <_mwryder@worldnet.att.net>:
> Morton Goldberg wrote:
> > On Jul 19, 2007, at 11:00 PM, Michael W. Ryder wrote:
> >
> >> I was trying to come up with a way to remove x instances of a
> >> character from a string and came up with a problem.  If I enter:
> >>
> >> a = "a b c d e f"
> >> for i in 1..3
> >>   a = a.sub!(' ', '')
> >> end
> >> puts a  ==> returns 'abcd e f' which is correct.
> >>
> >> But if I enter:
> >>
> >> a = "a b c d e f"
> >> for i in 1..10
> >>   a = a.sub!(' ', '')
> >> end
> >> puts a  ==> returns error.rb:3: private method `sub!' called for
> >> nil:NilClass (NoMethodError, and a is now nil.
> >>
> >> What I am looking for is a way to remove the first n instances of a
> >> blank from the string without wiping out the string if it does not
> >> contain at least n blanks.  I assume there is a way to do this with
> >> regular expressions, but have not found it yet.  This is something an
> >> editor I liked, UCEDIT, on the CDC Cyber had in the 70's.
> >
> > How about this?
> >
> > n = 3
> > "a b c d e f".sub(/(\S\s){#{n}}/) { |m| m.delete(" ") } # => "abcd e f"
> > n = 10
> > "a b c d e f".sub(/(\S\s){#{n}}/) { |m| m.delete(" ") } # => "a b c d e f"
> >
> > Regards, Morton
> >
>
> Is there nothing in regular expressions where you can tell it to do
> something up to n times?

There is - kind of.  You can use {} to give repetition counts.  You can do this

irb(main):004:0> a = "a b c d e f"
=> "a b c d e f"
irb(main):005:0> a.sub(/(?: [^ ]*){3}/) {|m| m.gsub(/ /, '') }
=> "abcd e f"
irb(main):006:0>

Kind regards

robert