Intersecting two multi-dimensional arrays

Toby

Hi there,

I have to arrays like

$offers[0]["user"] = "pete";
$offers[0]["id"] = "23";
...

$offers[1]["user"] = "max";
$offers[1]["id"] = "24";
...

$requests[0]["user"] = "pete";
$requests[0]["id"] = "23";
...

and so forth. Now what I want to do is intersect the arrays to get an array that contains all entries where $offers[]["id"] = $requests[]["id"]...

Is there an easy way of doing this?

Thanks for your help

ednark

great Knuth man!!! what are you doing...

store your information in two tables in a relational database, then ask the database to merge your tables and return your results as a php array

if for some reason you cannot do my first suggestion

use a foeach loop to step through $offers

in each iteration step through each item in requestst and test them

this will however get very expensive to do if each array is big at all.... you WANT to ask the relational database to do this logic for you

foeach ( $offrers as $offer )
  ///  now you have $offer['user'] and ['id']
  foreach ( $requests as $request )
    if ( $offer['id'] == $request['id'] )
      /// do whatever

Toby

my arrays come from a database, from a total of 7 tables...

but to compare all the entries in the database takes quite a long time.

here is what it is all about:

you can post offers (identifiable by id) and requests (identifiable by id) and you can search for offers by category. i query the database to find offers and request that match a request or offer from the user browsing the site.

what i get from the db, is

an array $offers with perfect matches from the table offers
an array $category with matches from the table offers
an array $requests with matches from the table requests.

now i need to display

all the offers where there is a request from the same user
all the offers that come from category where there is a request from the same user

i only want to query the db once, because the query puts considerable load on the db, that is why i would rather do it with the results. i don't know if that is much slower, as there are so many tables involved in the query...

ednark

but to compare all the entries in the database takes quite a long time.

not if you let the database do it for you..

this is why relational databases were designed... whoever wrote your database (probably mysql) spent many many many sleepless night trying to optimize how it compares all the entries in 7 tables...

you want to be able to do that on the SQL side, not the php side... there will be orders of magnitude difference...
the most expensive operation for a RDBMS is a table merge (for reasons i will not get into)

so perhaps you can collapse some of your 7 tables into fewer tables....

ask google to search for tutorials on putting databases into things called Noraml Forms 1st normal, 2nd normal, BCNF etc...

these give methods of minimizing table structure (or when you should make new tables)

to join more than 2 tables you often need to use more complex joins...

ask google for tutorials in inner and outer joins... they may be userfull to you...

basically your problem is solvable if you SQL skillz are l33+ enough... so work on studying up in that areas...

Toby

not if you let the database do it for you..

this is why relational databases were designed...
whoeverwrote your database (probably mysql) spent many many many sleepless night trying to optimize how it compares all the entries in 7 tables...

true, i did 😉

you want to be able to do that on the SQL side, not the php side... there will be orders of magnitude difference...
the most expensive operation for a RDBMS is a table merge (for reasons i will not get into)

so perhaps you can collapse some of your 7 tables into fewer tables....

nope.

ask google to search for tutorials on putting databases into things called Noraml Forms 1st normal, 2nd normal, BCNF etc...

the db is normalized.

ask google for tutorials in inner and outer joins... they may be userfull to you...

i am using joins.

basically your problem is solvable if you SQL skillz are l33+ enough... so work on studying up in that areas...

i can solve my problem with a couple of db queries (i actually have). i was just wondering if it makes sense, if i basically need to do two queries to get all the information that i need, if it makes more sense to query the db say 4 times or to take the results from the 2 queries and relate them via php. make sense?

ednark

ok well it does sound like you know what you are doing.... so i apologize ...

there is nothing wrong with using php to do your logic... if it's fast enough that is... there may be a smarter solution, but why waste a week trying to find it if you have working code...

however, i think your problem might not make sense to me unless i actually see your queries.... you seem to know enough to avoid the simple probmems. maybe post your queries and tables structure....