indexing alternative values inside arrays php

Question

A huge database values retriving problem i have simplified manually and giving here

in this code

$array = array(
  "0" => array("course_id" => 1,"register_number"=>"16BCA01"),
  "1" => array("course_id" => 1,"register_number"=>"16BCA02"),
  "2" => array("course_id" => 1,"register_number"=>"16BCA03"),
  "3" => array("course_id" => 1,"register_number"=>"16BCA04"),
  "4" => array("course_id" => 2,"register_number"=>"16BCA05"),
  "5" => array("course_id" => 2,"register_number"=>"16BCA06"),
  "6" => array("course_id" => 3,"register_number"=>"16BCA07"),
  "7" => array("course_id" => 3,"register_number"=>"16BCA08"),
  "8" => array("course_id" => 4,"register_number"=>"16BCA09"),
  "9" => array("course_id" => 4,"register_number"=>"16BCA10"),
  "10" => array("course_id" => 5,"register_number"=>"16BCA11"),
  "11" => array("course_id" => 5,"register_number"=>"16BCA12"),
  "12" => array("course_id" => 6,"register_number"=>"16BCA13"),
  "13" => array("course_id" => 6,"register_number"=>"16BCA14"),
  "14" => array("course_id" => 6,"register_number"=>"16BCA15"),
  "15" => array("course_id" => 7,"register_number"=>"16BCA16"),
  "16" => array("course_id" => 7,"register_number"=>"16BCA17"),
  "17" => array("course_id" => 7,"register_number"=>"16BCA18"),
  "18" => array("course_id" => 8,"register_number"=>"16BCA19"),
  "19" => array("course_id" => 8,"register_number"=>"16BCA20"),
  "20" => array("course_id" => 9,"register_number"=>"16BCA21")
) ;
print_r($array);

the answer will come like the course_id in sequential

   Array ( 
[0] => Array ( [course_id] => 1 [register_number] => 16BCA01 ) 
[1] => Array ( [course_id] => 1 [register_number] => 16BCA02 ) 
[2] => Array ( [course_id] => 1 [register_number] => 16BCA03 )
[3] => Array ( [course_id] => 1 [register_number] => 16BCA04 )
[4] => Array ( [course_id] => 2 [register_number] => 16BCA05 ) 
[5] => Array ( [course_id] => 2 [register_number] => 16BCA06 ) 
[6] => Array ( [course_id] => 3 [register_number] => 16BCA07 ) 
[7] => Array ( [course_id] => 3 [register_number] => 16BCA08 ) 
[8] => Array ( [course_id] => 4 [register_number] => 16BCA09 ) 
[9] => Array ( [course_id] => 4 [register_number] => 16BCA10 ) 
[10] => Array ( [course_id] => 5 [register_number] => 16BCA11 ) 
[11] => Array ( [course_id] => 5 [register_number] => 16BCA12 ) 
[12] => Array ( [course_id] => 6 [register_number] => 16BCA13 ) 
[13] => Array ( [course_id] => 6 [register_number] => 16BCA14 ) 
[14] => Array ( [course_id] => 6 [register_number] => 16BCA15 ) 
[15] => Array ( [course_id] => 7 [register_number] => 16BCA16 ) 
[16] => Array ( [course_id] => 7 [register_number] => 16BCA17 ) 
[17] => Array ( [course_id] => 7 [register_number] => 16BCA18 ) 
[18] => Array ( [course_id] => 8 [register_number] => 16BCA19 ) 
[19] => Array ( [course_id] => 8 [register_number] => 16BCA20 ) 
[20] => Array ( [course_id] => 9 [register_number] => 16BCA21 ) )

but i want the course_id to come in alternatives values like this

    Array ( 
[0] => Array ( [course_id] => 1 [register_number] => 16BCA01 ) 
[1] => Array ( [course_id] => 2 [register_number] => 16BCA05 ) 
[2] => Array ( [course_id] => 1 [register_number] => 16BCA02 ) 
[3] => Array ( [course_id] => 2 [register_number] => 16BCA06 ) 
[4] => Array ( [course_id] => 1 [register_number] => 16BCA03 ) 
[5] => Array ( [course_id] => 3 [register_number] => 16BCA07 ) 
[6] => Array ( [course_id] => 1 [register_number] => 16BCA04 ) 
[7] => Array ( [course_id] => 3 [register_number] => 16BCA08 )
[8] => Array ( [course_id] => 4 [register_number] => 16BCA09 ) 
[9] => Array ( [course_id] => 5 [register_number] => 16BCA11 )
[10] => Array ( [course_id] => 4 [register_number] => 16BCA10 ) 
[11] => Array ( [course_id] => 5 [register_number] => 16BCA12 ) 
[12] => Array ( [course_id] => 6 [register_number] => 16BCA13 ) 
[13] => Array ( [course_id] => 7 [register_number] => 16BCA16 ) 
[14] => Array ( [course_id] => 6 [register_number] => 16BCA14 ) 
[15] => Array ( [course_id] => 7 [register_number] => 16BCA17 )
[16] => Array ( [course_id] => 6 [register_number] => 16BCA15 ) 
[17] => Array ( [course_id] => 7 [register_number] => 16BCA18 ) 
[18] => Array ( [course_id] => 8 [register_number] => 16BCA19 ) 
[19] => Array ( [course_id] => 9 [register_number] => 16BCA21 )
[20] => Array ( [course_id] => 8 [register_number] => 16BCA20 ) )

course_id 1 and 2 should alternatively come first if either one id finished means it should move to the next id 3 or 4 likewise till end it should loop. Which means course_id should not repeat same values as previous value how to acheive this in php

Answer 1

You need to create your own logic. Using nested for loop and array functions you can achieve your requirements. Please see the below code, it will help you.

$array = array(
 "0" => array("course_id" => 1,"register_number"=>"16BCA01"),
 "1" => array("course_id" => 1,"register_number"=>"16BCA02"),
 "2" => array("course_id" => 1,"register_number"=>"16BCA03"),
 "3" => array("course_id" => 1,"register_number"=>"16BCA04"),
 "4" => array("course_id" => 2,"register_number"=>"16BCA05"),
 "5" => array("course_id" => 2,"register_number"=>"16BCA06"),
 "6" => array("course_id" => 3,"register_number"=>"16BCA07"),
 "7" => array("course_id" => 3,"register_number"=>"16BCA08"),
 "8" => array("course_id" => 4,"register_number"=>"16BCA09"),
 "9" => array("course_id" => 4,"register_number"=>"16BCA10"),
 "10" => array("course_id" => 5,"register_number"=>"16BCA11"),
 "11" => array("course_id" => 5,"register_number"=>"16BCA12"),
 "12" => array("course_id" => 6,"register_number"=>"16BCA13"),
 "13" => array("course_id" => 6,"register_number"=>"16BCA14"),
 "14" => array("course_id" => 6,"register_number"=>"16BCA15"),
 "15" => array("course_id" => 7,"register_number"=>"16BCA16"),
 "16" => array("course_id" => 7,"register_number"=>"16BCA17"),
 "17" => array("course_id" => 7,"register_number"=>"16BCA18"),
 "18" => array("course_id" => 8,"register_number"=>"16BCA19"),
 "19" => array("course_id" => 8,"register_number"=>"16BCA20"),
 "20" => array("course_id" => 9,"register_number"=>"16BCA21")
);

$new_array = array();
$k = 1;
for($i = 0; $i<=count($array);$i++)
{
   $i = 0;
   $new_array[]= $array[$i];    
   for($j=0;$j<=count($array);$j++)
   {
       if($array[$i]['course_id'] != $array[$j]['course_id'])
       {
          $new_array[]= $array[$j];
          unset($array[$i]);
          unset($array[$j]);
          $array = array_values($array);
          break;    
       }

    }

}
array_pop($new_array);
print_r($new_array);