Group rows of a 2d array by a column and create subarrays [duplicate]

Question

So I have a multidimensional array in the form (actual array can be much longer 500+ members)

$marr = array(
    array("s_id" => 1, 1.25 , 15),
    array("s_id" => 2, 0.75 , 25),
    array("s_id" => 1, 1.15 , 7) 
);

I am trying to break it into an array grouped/indexed by the s_id value of the member arrays

$sarr = array(
    1 => array(
        array("s_id" => 1, 1.25 , 15),
        array("s_id" => 1, 1.15 , 7) 
    ),
    2 => array(
        array("s_id" => 2, 0.75 , 25)
    )
);

Is there a built in function in php to do this or some best practice way of doing this?

why don't you use a database? instead of using multi-dimensional arrays. — Nahser Bakht
– Nahser Bakht, Commented Mar 3, 2013 at 17:32

Community · Accepted Answer · 2020-06-20 09:12:55Z

4

There is no built-in function that can supply this result. Instead, you need to iterate over the array, and check if the key matching the s_id value already exists. If it doesn't create a new array at that key.

$marr = array( array("s_id" => 1, 1.25 , 15),
               array("s_id" => 2, 0.75 , 25),
               array("s_id" => 1, 1.15 , 7) 
             ); 

// Holds the whole output
$output = array();

// Looping over the original array
foreach ($marr as $subarr) {
  // Check if the output array already has the s_id as a key
  if (!isset($output[$subarr['s_id']])) {
    // Initialize it
    $output[$subarr['s_id']] = array();
  }
  // Then append the current sub-array to the s_id array key
  $output[$subarr['s_id']][] = $subarr;
}
// Then call ksort() on the output array
// to sort the s_id keys in ascending order
ksort($output);

http://codepad.viper-7.com/SSBrAl

Prints:

Array
(
    [1] => Array
        (
            [0] => Array
                (
                    [s_id] => 1
                    [0] => 1.25
                    [1] => 15
                )

            [1] => Array
                (
                    [s_id] => 1
                    [0] => 1.15
                    [1] => 7
                )

        )

    [2] => Array
        (
            [0] => Array
                (
                    [s_id] => 2
                    [0] => 0.75
                    [1] => 25
                )

        )

)

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Mar 3, 2013 at 17:26

Michael Berkowski

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1 Comment

mickmackusa Dec 18, 2024 at 20:08

if (!isset($output[$subarr['s_id']])) { $output[$subarr['s_id']] = array(); } is entirely unneeded.

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