DuckDuckGo Regex Search • Hacker News Board

Re: DuckDuckGo Regex Search

#21

Post by pbhjpbhj » Tue, Jul 08, 2014, 12:36 PM UTC

oneeyedpigeon wrote: post #17

mike-cardwell wrote: post #12

Every comment here at time of writing is from people thinking that this is a way of searching the web using regular expressions. It is not. It is a way of taking a regular expression and an input and then applying that regular expression to that input. In this particular example it takes the regular expression: /(?x: (\w+) \s (\w+) )/ And applies it to: "hacker news" And then spits out the result: "hacker | news" Rep…

Thank you. Can you explain what "?x:" does? Searching for regular expressions syntax (another thing this doesn't do) is quite tricky.

http://regex101.com/ tells me:

>"x modifier: extended. Spaces and text after a # in the pattern are ignored" //

The other explainers I had to hand failed and/or called it an error.

Re: DuckDuckGo Regex Search

#22

Post by easytiger » Tue, Jul 08, 2014, 12:36 PM UTC

mike-cardwell wrote: post #12

Every comment here at time of writing is from people thinking that this is a way of searching the web using regular expressions. It is not. It is a way of taking a regular expression and an input and then applying that regular expression to that input. In this particular example it takes the regular expression: /(?x: (\w+) \s (\w+) )/ And applies it to: "hacker news" And then spits out the result: "hacker | news" Rep…

So.... it executes a regex?

Re: DuckDuckGo Regex Search

#23

Post by mike-cardwell » Tue, Jul 08, 2014, 12:38 PM UTC

easytiger wrote: post #22

mike-cardwell wrote: post #12

Every comment here at time of writing is from people thinking that this is a way of searching the web using regular expressions. It is not. It is a way of taking a regular expression and an input and then applying that regular expression to that input. In this particular example it takes the regular expression: /(?x: (\w+) \s (\w+) )/ And applies it to: "hacker news" And then spits out the result: "hacker | news" Rep…

So.... it executes a regex?

Yes. It's just a normal search term. Except for in the "Answers" section that DuckDuckGo sometimes provides when it thinks it knows the answer to what you're asking, it supplies the results of executing the regex.

Re: DuckDuckGo Regex Search

#24

Post by xg15 » Tue, Jul 08, 2014, 12:43 PM UTC

So, why again do we need a cloud service to test a regular expression?

Re: DuckDuckGo Regex Search

#25

Post by AlyssaRowan » Tue, Jul 08, 2014, 12:50 PM UTC

Awwww. I hoped for a moment it was literally searching the web with a regex. Unfortunately no, although it may be a handy regex cheat sheet.

Wake me when someone does this properly. It's only been done on a small scale or with very limited precomputed expressions, to my knowledge. Not many people would need it, but for those people it'd be insanely useful. But it's also insanely computationally hard - which means it'd be a really interesting technical achievement! There are no general-purpose reverse indexes that I know of that accelerate that as easily as keywords, but there are some data structures that might help a bit, although I can't think of practical ways to deploy them over arbitrary regexps specified at runtime! Plus some sanity heuristics and limits, of course, as regexps can undergo combinatorial explosion and some fun unexpected worse-case performance.

Re: DuckDuckGo Regex Search

#26

Post by gpvos » Tue, Jul 08, 2014, 12:51 PM UTC

Oh wait, I have to look at the text in the small grey bar above, and not at the list of search results. Still pretty non-obvious.

Re: DuckDuckGo Regex Search

#27

Post by elmindreda » Tue, Jul 08, 2014, 1:08 PM UTC

xg15 wrote: post #24

So, why again do we need a cloud service to test a regular expression?

I guess it's too much work to start a REPL.

Re: DuckDuckGo Regex Search

#28

Post by zeratul » Tue, Jul 08, 2014, 1:16 PM UTC

mike-cardwell wrote: post #12

Every comment here at time of writing is from people thinking that this is a way of searching the web using regular expressions. It is not. It is a way of taking a regular expression and an input and then applying that regular expression to that input. In this particular example it takes the regular expression: /(?x: (\w+) \s (\w+) )/ And applies it to: "hacker news" And then spits out the result: "hacker | news" Rep…

I agree. What the internet needs is semantics not regular expressions. If there is a need for regular expression, it's only because semantics is not working, for example, the search engine does not have all the synonyms so I might write "do|does|done". We should be focusing more on textual query expansion (if the query hides some background knowledge), auto-tagging of web pages (if the web pages assume some background knowledge) and clever disambiguation of queries (if we don't know which background knowledge tap into).

Re: DuckDuckGo Regex Search

#29

Post by mykhal » Tue, Jul 08, 2014, 1:52 PM UTC

s/Search/Eval/

Re: DuckDuckGo Regex Search

#30

Post by gmu3 » Tue, Jul 08, 2014, 2:26 PM UTC

dedosk wrote: post #3

Google does not implement regex search support because they said somewhere that the data storage needed for the index would be huge. And since regex search is used only by a small subset of users, it is not worth the effort.

I would guess that small subset of users is a big subset of users that use DDG.