# Doing an AND in regexp char class **URL:** \ **Category:** Ruby\ **Created:** [May 8, 2008, 11:41pm UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105 "2008-05-08T23:41:22Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 8, 2008, 11:41pm UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/1 "2008-05-08T23:41:22Z")
This question arises out of a couple of recent threads and may or may not be a Ruby-specific question. I can check with a character class if one of the characters in the class exists or does not exist, but can I use a regexp to check if a string absolutely contains all of the characters in the class? Using a set perspective, I can do it like this in irb… s1 = “hello there” s2 = “ohi” (s2.unpack(‘c\*’) & s1.unpack(‘c\*’)).size == s2.size =\> false I use unpack to avoid creating a bunch of String objects, one for each element in the array, which would happen if I used #split. What I’m wondering is if there is a way to do this with a simple regexp. Thanks, Todd ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 1:08am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/2 "2008-05-09T01:08:08Z")
On May 8, 2008, at 3:40 PM, Todd B. wrote: > s2 = “ohi” > (s2.unpack(‘c\*’) & s1.unpack(‘c\*’)).size == s2.size > > =\> false > > I use unpack to avoid creating a bunch of String objects, one for each > element in the array, which would happen if I used #split. What I’m > wondering is if there is a way to do this with a simple regexp. > > Thanks, > Todd cfp:~ \> cat a.rb class String def all\_chars? chars tr(chars, ‘’).empty? end end p ‘foobar’.all\_chars?(‘rabof’) p ‘foobar’.all\_chars?(‘abc’) p ‘foobar’.all\_chars?(‘’) cfp:~ \> ruby a.rb true false false a @ [http://codeforpeople.com/](http://codeforpeople.com/) ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 1:33am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/3 "2008-05-09T01:33:18Z")
On Thu, May 8, 2008 at 6:07 PM, ara.t.howard [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > Using a set perspective, I can do it like this in irb… > > p ‘foobar’.all\_chars?(‘rabof’) > p ‘foobar’.all\_chars?(‘abc’) > p ‘foobar’.all\_chars?(‘’) > > cfp:~ \> ruby a.rb > true > false > false Cool 🙂#tr is one of those useful methods I somehow consistently forget about. tkx fur realizashuns, Todd ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 1:52am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/4 "2008-05-09T01:52:03Z")
On May 8, 2008, at 5:30 PM, Todd B. wrote: > tr is one of those useful methods I somehow consistently forget about me too. just got lucky this time 😉 a @ [http://codeforpeople.com/](http://codeforpeople.com/) ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 1:34am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/5 "2008-05-09T01:34:28Z")
On Thu, May 8, 2008 at 5:40 PM, Todd B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > s2 = “ohi” > (s2.unpack(‘c\*’) & s1.unpack(‘c\*’)).size == s2.size > > =\> false > > I use unpack to avoid creating a bunch of String objects, one for each > element in the array, which would happen if I used #split. What I’m > wondering is if there is a way to do this with a simple regexp. REs can do this, but may not be the best way. The way that comes to mind is to see if the string matches the characters in any order, i.e. for “ohi” either ohi, oih, hio, hoi, iho, or ioh so something like /(o([^h]\*h[^i]i|[^i]\*i[^h]\*h)|(h([^i]\*i[^o]_o|[^o]_[^i]\*i)|o([^h]\*h[^o]\*o|[^o]\*o[^h]\*h)/ meaning o followed by either zero or more non-h’s folllowed by an h followed by zero or more non-i’s folllowed by an i or zero or more non-i’s followed by an i followed by zero or more non-h’s followed by an h or h followed by either … … I would be possible to generate such an RE from the string. But maybe someone cleverer with REs has a better approach. – Rick DeNatale My blog on Ruby [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/) ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 2:15am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/6 "2008-05-09T02:15:29Z")
On Thu, May 8, 2008 at 7:00 PM, Joel VanderWerf [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > > I can check with a character class if one of the characters in the > > > > > > tr(chars, ‘’).empty? > > > true > > > if chars.empty? > > > empty? > > > else > > > /\A[#{chars}]\*\z/ === self > > > end > > > end > > > end > > p ‘foobar’.all\_chars?(‘rabof’) # =\> true > p ‘foobar’.all\_chars?(‘abc’) # =\> false > p ‘foobar’.all\_chars?(‘’) # =\> false I’m drawing a blank here with this one. Why doesn’t this work then… irb(main):006:0\> r = /\A[oh]_\z/ =\> /\A[oh]_\z/ irb(main):007:0\> s = “hello, there” =\> “hello, there” irb(main):008:0\> r === s =\> false Todd ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 2:00am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/7 "2008-05-09T02:00:51Z")
Todd B. wrote: > > > Thanks, > > > p ‘foobar’.all\_chars?(’’) > > > > cfp:~ \> ruby a.rb > > true > > false > > false > > Cool 🙂#tr is one of those useful methods I somehow consistently forget about. But it can be done with regex, right? It’s just more elegant with tr. class String def all\_chars? chars if chars.empty? empty? else /\A[#{chars}]\*\z/ === self end end end p ‘foobar’.all\_chars?(‘rabof’) # =\> true p ‘foobar’.all\_chars?(‘abc’) # =\> false p ‘foobar’.all\_chars?(’’) # =\> false ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 2:26am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/8 "2008-05-09T02:26:35Z")
Todd B. wrote: > I’m drawing a blank here with this one. Why doesn’t this work then… > > irb(main):006:0\> r = /\A[oh]_\z/ > =\> /\A[oh]_\z/ > irb(main):007:0\> s = “hello, there” > =\> “hello, there” > irb(main):008:0\> r === s > =\> false Maybe I’m confused about was wanted originally. The above tests the following condition: (set of chars occurring in given string) is\_a\_subset\_of (given set of chars). irb(main):007:0\> /\A[oh]_\z/ === “hohoho” =\> true irb(main):008:0\> /\A[oh]_\z/ === “ho ho” =\> false If you want superset instead of subset, this works: irb(main):013:0\> /(?=.\*h)(?=.\*o)/ === “h o” =\> true ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 2:35am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/9 "2008-05-09T02:35:57Z")
Hi – On Fri, 9 May 2008, Joel VanderWerf wrote: > Maybe I’m confused about was wanted originally. The above tests the following > > If you want superset instead of subset, this works: > > irb(main):013:0\> /(?=.\*h)(?=.\*o)/ === “h o” > =\> true That depends on the order, though. To do the superset test, you could just do the subset, but in the other direction: check that the character class, as a string, doesn’t contain anything that isn’t in the main string: str = “h o” chars = “ho” /\A[#{str}]\*\z/ === chars # true (though probably best to uniquify the string first). David ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 2:31am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/10 "2008-05-09T02:31:51Z")
Hi – On Fri, 9 May 2008, Todd B. wrote: > > > > > =\> false > > > > > def all\_chars? chars > > > > > cfp:~ \> ruby a.rb > > > > > def all\_chars? chars > > > > > p ‘foobar’.all\_chars?(’’) # =\> false > > I’m drawing a blank here with this one. Why doesn’t this work then… > > irb(main):006:0\> r = /\A[oh]_\z/ > =\> /\A[oh]_\z/ > irb(main):007:0\> s = “hello, there” > =\> “hello, there” > irb(main):008:0\> r === s > =\> false “hello, there” contains letters other than o and h, but your regex calls for a string consisting of zero or more o’s or h’s and nothing else. I think there might be some confusion as between determining that a string contains certain characters, and determining that a string contains _only_ certain characters. My understanding was that you wanted the first, which you could do with tr but I think you’d probably want the character cluster to be doing the tr’ing: “oh”.tr(“hello, there”,"").empty? # true; all letters in “oh” # are also in “hello, there” “hello, there”.tr(“ho”,"").empty? # false They’re both strings, of course, so you can do either with Ara’s or Joel’s methods: “oh”.all\_chars?(“hello, there”) # true “hello, there”.all\_chars?(“oh”) # false though if it’s really the former you want you might want to name it all\_present\_in? or something. David ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 3:05am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/11 "2008-05-09T03:05:09Z")
Hi – On Fri, 9 May 2008, Joel VanderWerf wrote: > irb(main):004:0\> /(?=.\*h)(?=.\*o)/m === “o \nh” > =\> true > > Does that fix the order problem you were thinking of? Actually I think I was wrong about the order mattering (since they’re zero-width). But /m helps anyway. I still think you could just change the roles of the two strings and dissect “the string” as a character class and “the characters” as a string, and use your original technique. David ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 2:59am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/12 "2008-05-09T02:59:54Z")
David A. Black wrote: > > irb(main):013:0\> /(?=.\*h)(?=.\*o)/ === “h o” > > =\> true > > That depends on the order, though. Yes, it’s buggy. Should use //m: irb(main):003:0\> /(?=.\*h)(?=.\*o)/ === “o \nh” =\> false irb(main):004:0\> /(?=.\*h)(?=.\*o)/m === “o \nh” =\> true Does that fix the order problem you were thinking of? ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 9:18am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/13 "2008-05-09T09:18:46Z")
Joel VanderWerf wrote: > Todd B. wrote: > > > > > Thanks, > > > > p ‘foobar’.all\_chars?(’’) > > > > > > cfp:~ \> ruby a.rb > > > true > > > false > > > false > > > > Cool 🙂#tr is one of those useful methods I somehow consistently forget about. > > But it can be done with regex, right? It’s just more elegant with tr. > > class String > def all\_chars? chars > if chars.empty? > empty? > else > /\A[#{chars}]\*\z/ === self > end > end > end > > p ‘foobar’.all\_chars?(‘rabof’) # =\> true > p ‘foobar’.all\_chars?(‘abc’) # =\> false > p ‘foobar’.all\_chars?(’’) # =\> false Your method doesn’t work, which can clearly be seen in these examples: strs = [“aaa”, “bbb”, “ccc”] chars = “abc” strs.each do |str| if /\A[#{chars}]\*/ =~ str print str, " - yes" puts else print str, " - no" puts end end –output:– aaa - yes bbb - yes ccc - yes It should be clear from the output that even though the string “aaa” passes your test, it is not true that all the characters in the string “abc” appear in in the string “aaa”. ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 4:10am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/14 "2008-05-09T04:10:03Z")
On Thu, May 8, 2008 at 7:26 PM, Joel VanderWerf [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Maybe I’m confused about was wanted originally. The above tests the > following condition: > > (set of chars occurring in given string) > is\_a\_subset\_of > (given set of chars). Yep. The subject title is misleading, because the AND is already there [^ho] means not h _and_ also not o. I was looking to find if given a string A, can I say whether or not all of the characters in string A exist in string B (count doesn’t matter, just existence). All of you gave me some good answers that I hadn’t thought of. Good brain food 🙂 Todd ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 10:58am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/15 "2008-05-09T10:58:02Z")
Hi – On Fri, 9 May 2008, 7stud – wrote: > > > > false > > > > else > > puts > passes your test, it is not true that all the characters in the string > “abc” appear in in the string “aaa”. Do it the other way around (and don’t forget the \z): if /\A[#{str}]\*\z/ =~ chars It’s really the characters in str that you’re testing, to make sure that none of them fail to match the characters in chars. If the variable names seem backwards, you can change them. It’s the logic that’s important, and it works fine. David ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 12:09pm UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/16 "2008-05-09T12:09:50Z")
David A. Black wrote: > Hi – > > On Fri, 9 May 2008, 7stud – wrote: > > > > > > false > > > > > else > > > > puts > > passes your test, it is not true that all the characters in the string > > “abc” appear in in the string “aaa”. > > Do it the other way around (and don’t forget the \z): Whoops. > if /\A[#{str}]\*\z/ =~ chars > > It’s really the characters in str that you’re testing, to make sure > that none of them fail to match the characters in chars. If the > variable names seem backwards, you can change them. It’s the logic > that’s important, and it works fine. Nice. ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 11, 2008, 9:11am UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/17 "2008-05-11T09:11:01Z")
2008/5/9 ara.t.howard [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > class String > def all\_chars? chars > tr(chars, ‘’).empty? > end > end Using String#tr is nice, but the result is not what Todd wants: s1 = “hello there” s2 = “ohe” (s2.unpack(‘c\*’) & s1.unpack(‘c\*’)).size == s2.size =\> true class String def all\_chars? chars tr(chars, ‘’).empty? end end s1.all\_chars?(s2) =\> false Like in the regexp examples, you have to switch self and chars: class String def all\_chars? chars chars.tr(self, ‘’).empty? end end s1.all\_chars?(s2) =\> true Regards, Pit ---
**Author:** ![toadkicker](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/5fc32e/32.png) [@toadkicker](https://www.ruby-forum.com/u/toadkicker)\ **Post date:** [May 9, 2008, 12:02pm UTC](https://www.ruby-forum.com/t/doing-an-and-in-regexp-char-class/137105/18 "2008-05-09T12:02:04Z")
On Fri, May 9, 2008 at 1:50 AM, ara.t.howard [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > me too. just got lucky this time 😉 > Knowledge → the art of getting lucky very often, right Ara 😉 > we can deny everything, except that we have the possibility of being better. > simply reflect on that. > h.h. the 14th dalai lama > BTW when I was referring to the quote I learnt most about I was > thinking about “Be kind whenever it is possible. It is always > possible”. Not that I dislike the others or apply any judgment I just wanted to be clear that I _personally_ learnt the most from the above 🙂 Cheers Robert – [http://ruby-smalltalk.blogspot.com/](http://ruby-smalltalk.blogspot.com/) * * * Whereof one cannot speak, thereof one must be silent. Ludwig Wittgenstein