Group array rows by one column and only create a subarray from another column if more than one value

Question

How can I group row data from a two-dimensional array and only create a subarray of another column if the respective group contains more than one value?

In other words, I need to group rows by id and conditionally restructure an array of arrays to have a variable depth of either 2 or 3 levels.

Input:

[
    ['id' => 567, 'value' => 780],
    ['id' => 676, 'value' => 743],
    ['id' => 676, 'value' => 721],
    ['id' => 234, 'value' => 766],
    ['id' => 234, 'value' => 680]
]

Desired output:

[
    ['id' => 567, 'value' => 780],
    ['id' => 676, 'value' => [743, 721]],
    ['id' => 234, 'value' => [766, 680]]
]

Somewhat related: Group array data by column value and only create indexed subarrays if more than one occurrence — mickmackusa
– mickmackusa ♦, Commented Oct 14, 2022 at 23:10

Antony · Accepted Answer · 2013-01-24 08:05:44Z

Are you sure you want to have the value as an integer when there is one value and an array when there are more?

<?php
$array = array(
    array('id' => 567, 'value' => 780),
    array('id' => 676, 'value' => 743),
    array('id' => 676, 'value' => 721),
    array('id' => 234, 'value' => 766),
    array('id' => 234, 'value' => 680)
);

foreach ($array as $item) {
    $result[$item['id']][] = $item['value'];
}

foreach ($result as $id => $value) {
    if (count($value) > 1) {
        $output[] = array(
            'id' => $id,
            'value' => $value
        );
    } else {
        $output[] = array(
            'id' => $id,
            'value' => $value[0]
        );
    }
}

echo '<pre>';
print_r($output);
echo '</pre>';
?>

If not

<?php
$array = array(
    array('id' => 567, 'value' => 780),
    array('id' => 676, 'value' => 743),
    array('id' => 676, 'value' => 721),
    array('id' => 234, 'value' => 766),
    array('id' => 234, 'value' => 680)
);

foreach ($array as $item) {
    $result[$item['id']][] = $item['value'];
}

foreach ($result as $id => $value) {
    $output[] = array(
        'id' => $id,
        'value' => $value
    );
}

echo '<pre>';
print_r($output);
echo '</pre>';
?>

shukshin.ivan · Accepted Answer · 2013-01-24 08:01:22Z

try this one

$array['key1'] = array(
    0=>array('id'=>567, 'value'=>780),
    1=>array('id'=>676, 'value'=>743),
    2=>array('id'=>676, 'value'=>721),
    3=>array('id'=>234, 'value'=>766),
    4=>array('id'=>234, 'value'=>780)
    );

foreach($array['key1'] as $subarray){
    $group_id = $subarray['id'];

    if(!isset($return[$group_id]))
        $return[$group_id] = $subarray;
    else{
        if(is_array($return[$group_id]['value']))
            array_push($return[$group_id]['value'], $subarray['value']);
        else 
            $return[$group_id]['value'] = array($subarray['value'], $return[$group_id]['value']);
    }
}

// reset grouping keys into 0,1...
$return = array_values($return);
print_r($return);

j0k · Accepted Answer · 2013-01-24 08:11:57Z

There, all the work done for you. How easy is that!

//create the array as you have now
$array[0] = ['id'=>567, 'value'=>780];
$array[1] = ['id'=>676, 'value'=>743];
$array[2] = ['id'=>676, 'value'=>721];
$array[3] = ['id'=>234, 'value'=>766];
$array[4] = ['id'=>234, 'value'=>780];

print_r($array);
print chr(10).chr(10);

//create a new array with the values combined on key
$concat = array();
foreach($array as $val) {
  $i = $val['id'];
  $v = $val['value'];

  if (!is_array($concat[$i]))
    $concat[$i] = array();

  $concat[$i][] = $v;
}

print_r($concat);
print chr(10).chr(10);

//create a new array to show the data as you want.
$newarray = array();
foreach($concat as $key=>$val) {
  $t = array();
  $t['id'] = $key;

  if (count($val)==1)
    $t['value'] = $val[0];
  else {
    $t['value'] = array();
    foreach($val as $v)
      $t['value'][] = $v;
  } 

  $newarray[] = $t;
}

print_r($newarray);
print chr(10).chr(10);

Result:

Array
(
    [0] => Array
        (
            [id] => 567
            [value] => 780
        )

    [1] => Array
        (
            [id] => 676
            [value] => 743
        )

    [2] => Array
        (
            [id] => 676
            [value] => 721
        )

    [3] => Array
        (
            [id] => 234
            [value] => 766
        )

    [4] => Array
        (
            [id] => 234
            [value] => 780
        )

)


Array
(
    [567] => Array
        (
            [0] => 780
        )

    [676] => Array
        (
            [0] => 743
            [1] => 721
        )

    [234] => Array
        (
            [0] => 766
            [1] => 780
        )

)


Array
(
    [0] => Array
        (
            [id] => 567
            [value] => 780
        )

    [1] => Array
        (
            [id] => 676
            [value] => Array
                (
                    [0] => 743
                    [1] => 721
                )

        )

    [2] => Array
        (
            [id] => 234
            [value] => Array
                (
                    [0] => 766
                    [1] => 780
                )

        )

)

If you want to edit it, atleast do it right. If you remove the <pre> tags, then the print chr(10).chr(10) lines arent realy needed either anymore. Also I cant realy say you edit made the post any better.

goosman.lei · Accepted Answer · 2013-01-24 08:14:40Z

<?php
$arr['key1']    = array(
    array(
        'id'    => 567, 
        'value' => 780, 
    ), 
    array(
        'id'    => 676, 
        'value' => 743, 
    ), 
    array(
        'id'    => 676, 
        'value' => 721, 
    ), 
    array(
        'id'    => 234, 
        'value' => 766, 
    ), 
    array(
        'id'    => 234, 
        'value' => 780, 
    ), 
);

/* handle element merge */
function array_internal_merge_func($a, $b) {
    if ( is_array($a['value']) )
        $a['value'][]   = $b['value'];
    else 
        $a['value']     = array($a['value'], $b['value']);
    return $a;
}
/* handle array merge */
function array_internal_merge($array, $key, $merge_func) {
    $hashed = array();
    $result = array();
    foreach ( $array as $idx => $ele ) 
        $hashed[$ele[$key]][]   = $idx;
    foreach ( $hashed as $key => $idxies ) {
        reset($idxies);
        $idx0           = current($idxies);
        $result[$idx0]  = $array[$idx0];
        while ( $idx = next($idxies) ) 
            $result[$idx0]  = $merge_func($result[$idx0], $array[$idx]);
    }
    return $result;
}

print_r(array_internal_merge($arr['key1'], 'id', 'array_internal_merge_func'));

mickmackusa · Accepted Answer · 2022-10-14 22:46:18Z

This task can certainly be done concisely with one loop.

Use id column values as temporary first level keys. This makes identifying duplicates most efficient and easy.

While iterating:

if a row's id is new to the result array, then push the whole row (in its original, flat structure) into the result array; or
if a row's id was encountered before, then cast the stored row's value element as an array before pushing the current row's value into that subarray.

If you do not want your result to have id values as the first level keys, then call array_values() to re-index the result.

The special action done implemented below is that when casting a scalar or null data type to an array, the value becomes the lone element of the newly formed array. If an array is explicitly cast as an array, then there is no effect on the data structure at all. This is why (array) can be unconditionally applied in the else branch.

Code: (Demo)

foreach ($array as $row) {
    if (!isset($result[$row['id']])) {
        $result[$row['id']] = $row;
    } else {
        $result[$row['id']]['value'] = array_merge(
            (array) $result[$row['id']]['value'],
            [$row['value']]
        );
    }
}
var_export(array_values($result));

An alternative without array_merge(): (Demo)

foreach ($array as $row) {
    if (!isset($result[$row['id']])) {
        $result[$row['id']] = $row;
    } else {
        $result[$row['id']]['value'] = (array) $result[$row['id']]['value'];
        $result[$row['id']]['value'][] = $row['value'];
    }
}
var_export(array_values($result));

An alternative with array_reduce(): (Demo)

var_export(
    array_values(
        array_reduce(
            $array,
            function($result, $row) {
                if (!isset($result[$row['id']])) {
                    $result[$row['id']] = $row;
                } else {
                    $result[$row['id']]['value'] = (array) $result[$row['id']]['value'];
                    $result[$row['id']]['value'][] = $row['value'];
                }
                return $result;
            }
        )
    )
);

Collectives™ on Stack Overflow

Group array rows by one column and only create a subarray from another column if more than one value

5 Answers 5

Comments

Comments

1 Comment

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

Comments

Comments

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related