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comp.lang.ruby

String method to take subsections

Glenn

3/13/2008 12:18:00 AM

[Note: parts of this message were removed to make it a legal post.]

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
3 Answers

David A. Black

3/13/2008 12:53:00 AM

0

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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Thomas Wieczorek

3/13/2008 1:00:00 AM

0

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"].
>

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')

Paul Mckibbin

3/13/2008 1:41:00 AM

0

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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