Group data by multiple fields dynamically in PHP

Question

I want to group an associative array by fields. The array itself is originally from a mysql database query.

Below is an example of how I do it by hard coding it:

<?php
$fields = array("ID,subID");
$fieldCounts = count($fields);
$data = array(); //there is sql querieed data



$parsedData = array();

foreach ($data as $val)
{
    if ($fieldCounts == 1)
    {
        $f0 = $fields[0];
        $fv0 = $val[$f0];
        $parsedData[$fv0][] = $val;
    }
    else if ($fieldCounts == 2)
    {
        $f0 = $fields[0];
        $fv0 = $val[$f0];
        $f1 = $fields[10];
        $fv1 = $val[$f1];
        $parsedData[$fv0][$f1][] = $val;
    }
    else
    {
        exit("Third field not implemented");
    }
}
?>

But how can I do it dynamically with an arbitrary number of fields?

Answer 1

Am not sure how this code has worked for you but some things are that wrong and might not allow the code to function properly

• Fields has only as one valued with ,

  $fields = array("ID,subID"); 
                     ^----------- between string 
  

  Instead of

  $fields = array("ID","subID");
  

• Notice: Undefined offset:

  $f1 = $fields[10];
                 ^----- your array is not up to 10
  

Since you did not put your generate data and desired output. I would assume your final output and generate some temporary data

$fields = array("ID","subID"); //You can Increase or decrease this Fields
$fieldCounts = count($fields);
$data = array(); // there is sql querieed data

for($i = 0; $i < 3; $i ++) {
    $data[] = array("ID" => mt_rand(1, 1000),"subID" => "sub" . mt_rand(100, 900));
}

Ruining your code with the 2 corrections above

foreach ( $data as $val ) {
    if ($fieldCounts == 1) {
        $f0 = $fields[0];
        $fv0 = $val[$f0];
        $parsedData[$fv0][] = $val;
    } else if ($fieldCounts == 2) {
        $f0 = $fields[0];
        $fv0 = $val[$f0];
        $f1 = $fields[1];
        $fv1 = $val[$f1];
        $parsedData[$fv0][$f1][] = $val;
    } else {
        exit("Third field not implemented");
    }
}

Output

Array
(
    [159] => Array
        (
            [subID] => Array  <----------- SubID is fixed in your can cause confict
                (
                    [0] => Array
                        (
                            [ID] => 159
                            [subID] => sub589
                        )

                )

        )

    [334] => Array
        (
            [subID] => Array
                (
                    [0] => Array
                        (
                            [ID] => 334
                            [subID] => sub703
                        )

                )

        )

)

A better Alternative to yours

$parsedData = array();
foreach ( $data as $val ) {
    $temp = &$parsedData;
    foreach ( array_slice($val, 0, $fieldCounts) as $key ) {
        $temp = &$temp[$key];
    }
    $temp[] = $val;
}
print_r($parsedData);

Output

Array
(
    [159] => Array
        (
            [sub589] => Array <---------- Make Sub ID Dynamic 
                (
                    [0] => Array
                        (
                            [ID] => 159
                            [subID] => sub589
                        )

                )

        )

    [334] => Array
        (
            [sub703] => Array
                (
                    [0] => Array
                        (
                            [ID] => 334
                            [subID] => sub703
                        )

                )

        )

)

Recommended Version For easy array path

$parsedData = array();
foreach ( $data as $val ) {
    $temp = &$parsedData;
    foreach ( array_slice($val, 0, $fieldCounts) as $key ) {
        $temp = &$temp[$key];
    }
    $temp = $val; 
}
print_r($parsedData);

Output

Array
(
    [159] => Array
        (
            [sub589] => Array <---- Easy to asses as $parsedData['159']['sub589']
                (
                    [ID] => 159
                    [subID] => sub589
                )

        )

    [334] => Array
        (
            [sub703] => Array
                (
                    [ID] => 334
                    [subID] => sub703
                )

        )

)

Answer 2

Instead of doing if/elseif/else inside your $data foreach-loop (which is always limited to the number you "write" in there with that structure and a lot of code-duplicateion) you need to turn that if/elseif/else into a loop of it's own.

But first of all transform the existing code, I start in the first if body, it contains already all code necessary:

$f0  = $fields[0];
$fv0 = $val[$f0];
$parsedData[$fv0][] = $val;

The $val should be assigned to the array $parsedData which is keyed by $fields name $value. Let's compress this here, the number 0 in names is superfluous as we don't want it any longer (but maybe the first):

$field = $fields[0];
$value = $values[$field];

$parsedData[$value][] = $values;

(I changed $val into $values to improve naming). This is now more easy to read and understand. Also we spot the magic number 0 here more easily.

Now to the magic. We want to add to an array here (push):

$parsedData[$value][] = $values;

To make this more easy, let's turn it this way:

$array   = &$parsedData[$value];
$array[] = $values;

This right now seems superfluous, but when this turns into a loop, it will become more clear:

$array   = &$parsedData;

...

$array   = &array[$value];

...

$array[] = $values;

Let's review the code in with the outer loop at this moment:

foreach ($data as $values)
{

    $array   = &$parsedData; 

    $field = $fields[0];
    $value = $values[$field];        
    $array = &$array[$value];

    $array[] = $values;
}

Obviously this code is yet not complete. The inner-loop is missing but it starts to get some kind of body. And actually the inner loop is pretty simple to achieve:

$array   = &$parsedData; 

foreach ($fields as $field)
{
    $value = $values[$field];
    $array = &$array[$value];
}

$array[] = $values;

And that's already it. The single field has been turned into an iteration over all fields. The aliasing/referencing of the sub-array per each step in the iteration allows to push the value to the appropriate array entry after the inner loop has finished.

The whole outer and inner loop:

foreach ($data as $values)
{
    $array   = &$parsedData; # set reference

    foreach ($fields as $field)
    {
        $value = $values[$field];
        $array = &$array[$value];
    }

    $array[] = $values;

    unset($array); # remove reference
}