how to do this?

TechMech

Hi,

I have a problem and was wondering if anyone has any ideas.

I have an array with 6 numbers in it. IE 1,5,7,11,12,66

I have a master array with 6 numbers in it. IE 1,4,6,11,43,66

I want to know how many numbers in array 1 matched array 2. In the above example, the answer would be 3.

The problem is I need to run lots of arrays against the master one after the other and get counts. Any ideas on how to do this without crashing anything? 😕

THANKS!

matt_4013

Not entirely sure what you're trying to accomplish here, so I could be off the mark, but unless you're running a really bad server with a lot of users, just a normal loop for the master array using the
in_array function should be fine.

$count = 0;
foreach($master_array as $v) {

if(in_array($v, $array)) {
	$count++;
}
}

TechMech

matt_4013,

Thanks. I will try it. My server is a dual 1.3 ghz processor and 2 gigs of ram.

I was just concerned as I need to run about 1 million arrays against the master.

This of course would be broken down in clusters of around 5000 or so each.

I just never did that on a grand scale so was not sure if there was any super fast way.

Thanks!

matt_4013

I've never worked on that kind of scale before, so there is no disclaimer here. The script might take a while to run, and might also use more than it's allocated 8MB of RAM though, so I would suggest editing the timeout and the maximum memory usage in the php.ini. That's a hell of a lot of records!

BuzzLY

would this be faster? If you have to do it a million times, you would want to use a function that was as fast as possible:

$count = count (array_intersect ( $array1, $array2 ));

matt_4013

I wouldn't have thought that would be faster. I suppose the easiest way to tell is to just create something that will time the execution and benchmark it on a smaller data set. Can you get back to us? I'm very curious about this! 🙂

BuzzLY

Interestingly, manually looping is much faster than array_intersect...

I am attaching a sample PHP script used to test both functions. You should be able to simply save it in htdocs and load it up in your browser. Make sure you rename it with the .php extension... When I ran it, this is what it returned:

Timing ***************************************************
Start: 0.000 0.000
First Loop End: 3.713 3.713

Elapsed time: 3.713

Timing ***************************************************
Start: 0.000 0.000
Second Loop End: 8.367 8.367

Elapsed time: 8.367

The first loop was the manual looping, the second loop was using count(array_intersect($array1, $array2)). In both cases, I looped 100,000 times.

There must be a lot of overhead in that PHP function...

matt_4013

Yeah, that's what I expected. I find that it's usually much faster with less ram and processing used if i write my own functions specific to what I'm doing. Things like wordwrap and this one are good examples. It does however, take much longer to code! Not really in this instance, but you get the general idea.

TechMech

Very good man.
Last night I was thinking that the function routine would be slower as I had no clue what was actually in the function.

Matt blew their function out of the water 🙂

Thanks guys!