String method to take subsections

ruby-talk
1

Hi,

I'm looking for a method for the String class that returns an array of strings based on two input strings.

For example, if you had the string 'xxxxxa1byyyyya2bzzzzzzz' I'd like it to return the smaller strings between 'a' and b', but I don't want the smaller strings to include either 'a' or 'b'.

So, 'xxxxxa1byyyyya2bzzzzzzz'.method_x('a', 'b') would return ["1", "2"].

If you had the string 'a1b2' and tried 'a1b2'.method_x('a', 'c') you'd get nil because 'c' is obviously not in the String that's calling the method.

Likewise, if you tried 'a1b2'.method_x('b', 'a') it would also return nil since there's no string between 'b' and 'a' (so the order matters).

I looked but didn't see anything quite like this.

Thanks!

Glenn

2

Hi --

···

On Thu, 13 Mar 2008, Glenn wrote:

Hi,

I'm looking for a method for the String class that returns an array of strings based on two input strings.

For example, if you had the string 'xxxxxa1byyyyya2bzzzzzzz' I'd like it to return the smaller strings between 'a' and b', but I don't want the smaller strings to include either 'a' or 'b'.

So, 'xxxxxa1byyyyya2bzzzzzzz'.method_x('a', 'b') would return ["1", "2"].

If you had the string 'a1b2' and tried 'a1b2'.method_x('a', 'c') you'd get nil because 'c' is obviously not in the String that's calling the method.

Likewise, if you tried 'a1b2'.method_x('b', 'a') it would also return nil since there's no string between 'b' and 'a' (so the order matters).

I looked but didn't see anything quite like this.

Have a look at String#scan.

   'xxxxxa1byyyyya2bzzzzzzz'.scan(/a(.*?)b/)
   => [["1"], ["2"]]

It may not be an exact fit for the calling syntax you want but you
could wrap it in something else.

David

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3

You could use String#scan and wrap it in a method or extend the String class:

# So, 'xxxxxa1byyyyya2bzzzzzzz'.method_x('a', 'b') would return ["1", "2"].

def method_x(str, first, last)
    pattern = "#{first}(\\d)#{last}"
    regexp = Regexp.new(pattern)
    return str.scan(regexp).flatten
end

p method_x('xxxxxa1byyyyya2bzzzzzzz', 'a', 'b') #=> ["1", "2"].

# you could also extend the String class
class String
    def method_x(first, last)
        pattern = "#{first}(\\d)#{last}"
        regexp = Regexp.new(pattern)
        return self.scan(regexp).flatten
    end
end

p 'xxxxxa1byyyyya2bzzzzzzz'.method_x('a', 'b')

···

On Thu, Mar 13, 2008 at 1:18 AM, Glenn <glenn_ritz@yahoo.com> wrote:

So, 'xxxxxa1byyyyya2bzzzzzzz'.method_x('a', 'b') would return ["1", "2"].

4

Glenn wrote:

Hi,

I'm looking for a method for the String class that returns an array of
strings based on two input strings.

Regular expressions are your friend here:

class String
  def containedby(startmark='a',endmark='b')
    self.scan(Regexp.new(startmark+'([^'+endmark+']*)'+endmark)).flatten
  end
end

should do what you want. If you want to restrict it to just one
character remove the * in ']*)'.

If you had the string 'a1b2' and tried 'a1b2'.method_x('a', 'c') you'd
get nil because 'c' is obviously not in the String that's calling the
method.

Likewise, if you tried 'a1b2'.method_x('b', 'a') it would also return
nil since there's no string between 'b' and 'a' (so the order matters).

Actually returns in both these cases, but I'm sure you can deal with
those.

Test Listing and output below:

···

====================================
class String
  def containedby(startmark='a',endmark='b')
    self.scan(Regexp.new(Regexp.escape(startmark)+'([^'+Regexp.escape(endmark)+']*)'+Regexp.escape(endmark))).flatten
  end
end

TEST='xxxxxa1byyyyya2bzzzzzzz'
extracted=TEST.containedby('a','b')
puts extracted.inspect
extracted=TEST.containedby('a','c')
puts extracted.inspect
TEST2='b1a2'
extracted=TEST2.containedby('a','b')
puts extracted.inspect

=====================================

["1", "2"]


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