Boolean search in strings

[Anon]

Hello everyone,

I guess I need some help to build a boolean-like regular expression using preg_match_all ($boolean-like-expression,$text,$matches).

Given that

$text: is a given text (say a web page containing an article on house gardening)

$matches is the returned array of keywords found

$boolean-like-expression: is a user defined set of keywords (say \'house AND garden\') to be matched against the $text content.

So far I was only capable to get the OR operator working by using the alternate pattern separator \'|\' in a expression like:

$boolean-like-expression:\"/\bhouse\b|\bgarden\b/i\";
(Will return true if the word house OR the word garden is found)

But more complex searches like \'word1 AND word2\' or \'(word1 AND word2) OR word3\' seam to be impossible using PCRE

Can someone advise me on that? I must say I am not so good in Perl regular expressions but I have the feeling that I will need to use a database to search with boolean operators.

Vin

[[deleted]]

Regexps can only find patterns in sequence.
So if you want to do an AND, you could only do 'A AND B' or 'B AND A', not 'A AND B in random order'.
If you need to get that, just run two regexps.

A database is probably better because you can pre-process the data and get much more complex results (hitcounts etc)

[Anon]

Thanks Vincent,

how do you actually state the AND operator?

I tried with:

/\bhouse\w+\bgarden\b/i

assuming that the word house was preceeding garden but I couldn't find anything (say in a string like: my house has a green garden).

[[deleted]]

there is no AND. You can only match on 'house(somethingelse)garden'

$sString = "my house has a green garden";
if (preg_match('/house.*?garden/', $sString))
{
echo 'found';
}
else
{
echo 'not found';
};

this will not match if house and garden are reversed. To match that you'd need to also reverse the pattern. So if you have five keywords, you'd need a ton of patterns to do AND, or just one pattern per keyword and do the AND in PHP itself, something like:

if (preg_match('/house/', $sString) AND preg_match('/garden/', $sString))

But at that point it may be wise to benchmark it and see if things like strpos might be faster.