RE: [PHP] Antithesis to array_unique

> -----Original Message----- > From: David Nicholson [mailto:me@djnicholson.com] > Sent: 09 July 2003 15:08 > > This is a reply to an e-mail that you wrote on Wed, 9 Jul > 2003 at 14:55, > lines prefixed by '>' were originally written by you. > > Having STFM I am wondering if anyone knows of a quick antithesis to > > array_unique? We have an array in which we need to return all > > duplicate > > values instead of the non-duplicates.=20 > > How about: > > $array1 = array("dupe","dupe","another item"); > $valuecount = array(); > foreach($array1 as $value){ > if(isset($valuecount[$value])){ > $valuecount[$value]++; > } else { > $valuecount[$value] = 1; > } > } > $dupes = array(); > foreach($valuecount as $value=>$count){ > if($count>1){ > array_push($dupes,$value); > } > } > // $dupes now contains all duplicate values. > > There may be a quicker way of doing it though... Well, for a kick-off, how about making use of array_count_values() (http://www.php.net/array_count_values)? $array1 = array("dupe","dupe","another item"); $dupes = array(); foreach(array_count_values($array1) as $value=>$count){ if($count>1){ $dupes[] = $value; } } I think judicious applications of array_unique() and array_diff() could also do the job, although I don't know how this compares for efficiency: $dupes = array_unique(array_diff($array1, array_unique($array1))); Cheers! Mike --------------------------------------------------------------------- Mike Ford, Electronic Information Services Adviser, Learning Support Services, Learning & Information Services, JG125, James Graham Building, Leeds Metropolitan University, Beckett Park, LEEDS, LS6 3QS, United Kingdom Email: m.ford@lmu.ac.uk Tel: +44 113 283 2600 extn 4730 Fax: +44 113 283 3211