php - Count specific array values with same part -

i found lot of samples how count positions or occurrences in arrays actualy doesnt solve problem.

my array looks like:

$foo = array(           "foo"=>"bar",           "bar"=>"foo",           "hello"=>"world",           "world"=>"hello",           "grt1"=>"a",           "grt2"=>"b",           "grt3"=>"c",           "grt4"=>"d",           "grt5"=>"e",           "gr1"=>2,           "gr2"=>0,           "gr3"=>,           "gr4"=>5,           "gr5"=> ) 

what want achive count how many gr{i} in array.

the thing is, dont want count grt{i}. result sample should 5.

array_count_values not me in case.

my try atm is:

$count = 0; for($i=0;$i<count($foo);$i++){     if(array_key_exists("gr".$i, $foo)){         $count++     } } 

is way ? or there nicer way ?

edit: since need result loop (for) rid of loop.

array_reduce() job

$count = array_reduce(array_keys($foo), function($c, $k){   return preg_match('/^gr\d+$/', $k) ? ++$c : $c; }, 0);