Tried to use an example below (#56022) for array_chunk_fixed that would "partition" or divide an array into a desired number of split lists -- a useful procedure for "chunking" up objects or text items into columns, or partitioning any type of data resource. However, there seems to be a flaw with array_chunk_fixed — for instance, try it with a nine item list and with four partitions. It results in 3 entries with 3 items, then a blank array.

So, here is the output of my own dabbling on the matter:

<?php

function partition( $list, $p ) {
    $listlen = count( $list );
    $partlen = floor( $listlen / $p );
    $partrem = $listlen % $p;
    $partition = array();
    $mark = 0;
    for ($px = 0; $px < $p; $px++) {
        $incr = ($px < $partrem) ? $partlen + 1 : $partlen;
        $partition[$px] = array_slice( $list, $mark, $incr );
        $mark += $incr;
    }
    return $partition;
}

$citylist = array( "Black Canyon City", "Chandler", "Flagstaff", "Gilbert", "Glendale", "Globe", "Mesa", "Miami",
                   "Phoenix", "Peoria", "Prescott", "Scottsdale", "Sun City", "Surprise", "Tempe", "Tucson", "Wickenburg" );
print_r( partition( $citylist, 3 ) );

?>

Array
(
    [0] => Array
        (
            [0] => Black Canyon City
            [1] => Chandler
            [2] => Flagstaff
            [3] => Gilbert
            [4] => Glendale
            [5] => Globe
        )

    [1] => Array
        (
            [0] => Mesa
            [1] => Miami
            [2] => Phoenix
            [3] => Peoria
            [4] => Prescott
            [5] => Scottsdale
        )

    [2] => Array
        (
            [0] => Sun City
            [1] => Surprise
            [2] => Tempe
            [3] => Tucson
            [4] => Wickenburg
        )

)

To reverse an array_chunk, use array_merge, passing the chunks as a variadic:

<?php
$array = [1, 2, 3, 4, 5, 6, 7, 8, 9];

$chunks = array_chunk($array, 3);
// $chunks = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

$de_chunked = array_merge(…$chunks);
// $de_chunked = [1, 2, 3, 4, 5, 6, 7, 8, 9]
?>

If you just want to grab one chunk from an array, you should use array_slice().

Most easy way split array to parts

<?php

$arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

print_r(array_chunk($arr, ceil(count($arr) / 2)));
// return: [[1, 2, 3, 4, 5], [6, 7, 8, 9, 10]]

print_r(array_chunk($arr, ceil(count($arr) / 3)));
// return: [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10]]

?>

Here my array_chunk_values( ) with values distributed by lines (columns are balanced as much as possible) :

<?php
    function array_chunk_vertical($data, $columns) {
        $n = count($data) ;
        $per_column = floor($n / $columns) ;
        $rest = $n % $columns ;

        // The map
        $per_columns = array( ) ;
        for ( $i = 0 ; $i < $columns ; $i++ ) {
            $per_columns[$i] = $per_column + ($i < $rest ? 1 : 0) ;
        }

        $tabular = array( ) ;
        foreach ( $per_columns as $rows ) {
            for ( $i = 0 ; $i < $rows ; $i++ ) {
                $tabular[$i][ ] = array_shift($data) ;
            }
        }

        return $tabular ;
    }

    header('Content-Type: text/plain') ;

    $data = array_chunk_vertical(range(1, 31), 7) ;
    foreach ( $data as $row ) {
        foreach ( $row as $value ) {
            printf('[%2s]', $value) ;
        }
        echo "\r\n" ;
    }

    /*
        Output :

        [ 1][ 6][11][16][20][24][28]
        [ 2][ 7][12][17][21][25][29]
        [ 3][ 8][13][18][22][26][30]
        [ 4][ 9][14][19][23][27][31]
        [ 5][10][15]
    */
?>

Response to azspot at gmail dot com function partition.

$columns = 3;
$citylist = array('Black Canyon City', 'Chandler', 'Flagstaff', 'Gilbert', 'Glendale', 'Globe', 'Mesa', 'Miami', 'Phoenix', 'Peoria', 'Prescott', 'Scottsdale', 'Sun City', 'Surprise', 'Tempe', 'Tucson', 'Wickenburg');
print_r(array_chunk($citylist, ceil(count($citylist) / $columns)));

Output:
Array
(
    [0] => Array
        (
            [0] => Black Canyon City
            [1] => Chandler
            [2] => Flagstaff
            [3] => Gilbert
            [4] => Glendale
            [5] => Globe
        )

    [1] => Array
        (
            [0] => Mesa
            [1] => Miami
            [2] => Phoenix
            [3] => Peoria
            [4] => Prescott
            [5] => Scottsdale
        )

    [2] => Array
        (
            [0] => Sun City
            [1] => Surprise
            [2] => Tempe
            [3] => Tucson
            [4] => Wickenburg
        )

)

chunk array vertically

$arr    = range(1, 19);
function array_chunk_vertical($arr, $percolnum){
    $n = count($arr);
    $mod    = $n % $percolnum;
    $cols   = floor($n / $percolnum);
    $mod ? $cols++ : null ;
    $re     = array();
    for($col = 0; $col < $cols; $col++){
        for($row = 0; $row < $percolnum; $row++){
            if($arr){
                $re[$row][]   = array_shift($arr);
            }
        }
    }
    return $re;
}
$result = array_chunk_vertical($arr, 6);
foreach($result  as $row){
    foreach($row as $val){
        echo '['.$val.']';
    }
    echo '<br/>';
}
/*
[1][7][13][19]
[2][8][14]
[3][9][15]
[4][10][16]
[5][11][17]
[6][12][18]
 */

Had need to chunk an object which implemented ArrayAccess Iterator Countable.  array_chunk wouldn't do it.  Should work for any list of things

<?php
   $listOfThings = array(1,2,3,4,5,6,7,8,9,10,11,12,13);
   print_r(chunk_iterable($listOfThings, 4);

  function chunk_iterable($listOfThings, $size) {
      $chunk = 0;
      $chunks = array_fill(0, ceil(count($listOfThings) / $size) - 1, array());
      $index = 0;
      foreach($listOfThings as $thing) {
        if ($index && $index % $size == 0) $chunk++;
        $chunks[$chunk][] = $thing;
        $index++;
      }
      return $chunks;
  }
?>

<table>
<tr>
<?php

$array_chunkdata = array(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25);
$chunk  = array_chunk($array_chunkdata,5);
$rev_counter = 2;

function for_chunk($chunk_data){

    echo "<td><table>";

      foreach($chunk_data as $key => $chunk_value)
      {
        echo "<tr><td>";
        echo $chunk_value;
        echo "</td></tr>";
      }
      echo "</table></td>";   

}

foreach($chunk as $key => $chunk_data)
{
    if($rev_counter%2==0)
    {   
      for_chunk($chunk_data);
    }
    else
    {
      $chunk_data =  array_reverse($chunk_data);
      
      for_chunk($chunk_data);
     
    } 
  $rev_counter++;
}
?> 
</tr>
</table>
/*
Output:
1
2
3
4
5
    
10
9
8
7
6
    
11
12
13
14
15
    
20
19
18
17
16
    
21
22
23
24
25
*/

array_chunk() is helpful when constructing tables with a known number of columns but an unknown number of values, such as a calendar month. Example:

<?php

$values = range(1, 31);
$rows = array_chunk($values, 7);

print "<table>\n";
foreach ($rows as $row) {
    print "<tr>\n";
    foreach ($row as $value) {
        print "<td>" . $value . "</td>\n";
    }
    print "</tr>\n";
}
print "</table>\n";

?>

Outputs:

1 2 3 4 5 6 7 
8 9 10 11 12 13 14 
15 16 17 18 19 20 21 
22 23 24 25 26 27 28 
29 30 31 

The other direction is possible too, with the aid of a function included at the bottom of this note. Changing this line:
  $rows = array_chunk($values, 7);

To this:
  $rows = array_chunk_vertical($values, 7);

Produces a vertical calendar with seven columns:

1 6  11 16 21 26 31 
2 7  12 17 22 27 
3 8  13 18 23 28 
4 9  14 19 24 29 
5 10 15 20 25 30 

You can also specify that $size refers to the number of rows, not columns:
  $rows = array_chunk_vertical($values, 7, false, false);

Producing this:

1 8  15 22 29 
2 9  16 23 30 
3 10 17 24 31 
4 11 18 25 
5 12 19 26 
6 13 20 27 
7 14 21 28 

The function:

<?php

function array_chunk_vertical($input, $size, $preserve_keys = false, $size_is_horizontal = true)
{
    $chunks = array();
    
    if ($size_is_horizontal) {
        $chunk_count = ceil(count($input) / $size);
    } else {
        $chunk_count = $size;
    }
    
    for ($chunk_index = 0; $chunk_index < $chunk_count; $chunk_index++) {
        $chunks[] = array();
    }

    $chunk_index = 0;
    foreach ($input as $key => $value)
    {
        if ($preserve_keys) {
            $chunks[$chunk_index][$key] = $value;
        } else {
            $chunks[$chunk_index][] = $value;
        }
        
        if (++$chunk_index == $chunk_count) {
            $chunk_index = 0;
        }
    }
    
    return $chunks;
}

?>

[Editors note: This function was based on a previous function by gphemsley at nospam users dot sourceforge.net]

For those of you that need array_chunk() for PHP < 4.2.0, this function should do the trick:

<?php
if (!function_exists('array_chunk')) {
    function array_chunk( $input, $size, $preserve_keys = false) {
        @reset( $input );
        
        $i = $j = 0;

        while( @list( $key, $value ) = @each( $input ) ) {
            if( !( isset( $chunks[$i] ) ) ) {
               $chunks[$i] = array();
            }

            if( count( $chunks[$i] ) < $size ) {
                if( $preserve_keys ) {
                    $chunks[$i][$key] = $value;
                    $j++;
                } else {
                    $chunks[$i][] = $value;
                }
            } else {
                $i++;

                if( $preserve_keys ) {
                    $chunks[$i][$key] = $value;
                    $j++;
                } else {
                    $j = 0;
                    $chunks[$i][$j] = $value;
                }
            }
        }

        return $chunks;
    }
}
?>

This function can be used to reverse effect of <?php array_Chunk()?>.
<?php
function array_Unchunk($array)
{
    return call_User_Func_Array('array_Merge',$array);
}

header('Content-Type: text/plain');
$array=array(
    array(
            'Black Canyon City',
            'Chandler',
            'Flagstaff',
            'Gilbert',
            'Glendale',
            'Globe',
    ),
    array(
            'Mesa',
            'Miami',
            'Phoenix',
            'Peoria',
            'Prescott',
            'Scottsdale',
    ),
    array(
            'Sun City',
            'Surprise',
            'Tempe',
            'Tucson',
            'Wickenburg',
    ),
);
var_Dump(array_Unchunk($array));
?>

Output:
array(17) {
  [0]=>
  string(17) "Black Canyon City"
  [1]=>
  string(8) "Chandler"
  [2]=>
  string(9) "Flagstaff"
  [3]=>
  string(7) "Gilbert"
  [4]=>
  string(8) "Glendale"
  [5]=>
  string(5) "Globe"
  [6]=>
  string(4) "Mesa"
  [7]=>
  string(5) "Miami"
  [8]=>
  string(7) "Phoenix"
  [9]=>
  string(6) "Peoria"
  [10]=>
  string(8) "Prescott"
  [11]=>
  string(10) "Scottsdale"
  [12]=>
  string(8) "Sun City"
  [13]=>
  string(8) "Surprise"
  [14]=>
  string(5) "Tempe"
  [15]=>
  string(6) "Tucson"
  [16]=>
  string(10) "Wickenburg"
}

Hi, I've made  a function to split an array into chunks based on columns wanted. For example:

<?php $a = array(1,2,3,4,5,6,7,8); ?>

goal (say, for 3 columns):

<?php
array(
   array(1,2,3),
   array(4,5,6),
   array(7,8)
);
?>

<?php
function get_array_columns($array, $columns){
        
        $columns_map = array();
        for($i=0; $i<$columns; $i++){ $columns_map[] = 0; }//init columns
        
        //create map
        $count = count($array);
        $position = 0;
        while($count > 0){
            $columns_map[$position]++;
            $position = ($position < $columns-1) ? ++$position : 0;
            $count--;
        }

        //chunk the array based on map
        $chunked = array();
        foreach($columns_map as $map){
            $chunked[] = array_splice($array,0,$map);
        }
        
        return $chunked;
    }//end get_array_columns
?>

With no luck finding a function; here is the one I wrote:
It will evenly distribute items into a fixed amount of groups but also keeps items that were sorted close together to be in the same output groups.
<?php
function distributed_array_chunk(array $items, int $groups, bool $preserveKeys = false) {

    $grouped = [];
    $groupsPerItem = $groups /  count($items);
    $progress = 0.00;

    foreach ($items as $key => $value) {

        $index = floor($progress += $groupsPerItem);

        if ($preserveKeys) {
            $grouped[$index][$key] = $value;
        }
        else{
            $grouped[$index][] = $value;
        }    
    }

    return $grouped;
}
?>

This function takes each few elements of an array and averages them together. It then places the averages in a new array. It is used to smooth out data. For example lets say you have a years worth of hit data to a site and you want to graph it by the week. Then use a bucket of 7 and graph the functions output.

function array_bucket($array, $bucket_size)  // bucket filter
{
    if (!is_array($array)) return false; // no empty arrays
    $buckets=array_chunk($array,$bucket_size);  // chop up array into bucket size units
    foreach ($buckets as $bucket) $new_array[key($buckets])=array_sum($bucket)/count($bucket);
    return $new_array;  // return new smooth array
}

A breakdown by groups with excess:

function array_chunk_greedy($arr, $count){
    $arr = array_chunk($arr, $count);
    if(($k = count($arr)-1) > 0){    
        if(count($arr[$k]) < $count){
            $arr[$k-1] = array_merge($arr[$k-1], $arr[$k]);
            unset($arr[$k]);
        }            
    }
    return $arr;    
}

$arr = range(1, 13);
$arr = array_chunk_greedy($arr, 4);

print_r($arr);

[1,2,3,4,5,6,7,8,9,10,11,12,13] —> [1,2,3,4] [5,6,7,8] [9,10,11,12,13]

More examples:

[1,2,3,4,5,6,7,8,9,10,11,12] —> [1,2,3,4] [5,6,7,8] [9,10,11,12]
[1,2,3,4,5,6,7,8,9,10,11,12,13] —> [1,2,3,4] [5,6,7,8] [9,10,11,12,13]
[1,2,3,4,5,6,7,8,9,10,11,12,13,14] —> [1,2,3,4] [5,6,7,8] [9,10,11,12,13,14]
[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15] —> [1,2,3,4] [5,6,7,8] [9,10,11,12,13,14,15]
[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] —> [1,2,3,4] [5,6,7,8] [9,10,11,12] [13,14,15,16]

Example report:

$arr = range(1, 45);
$arr = array_chunk_lazy($arr, 10);

$arr = array_map(function($sub_value) {
            return implode('<br>', $sub_value);
        }, $arr);

$title = '<h2>title</h2>';
$arr = $title.implode($title, $arr).$title;

echo $arr;

based on the same syntax, useful about making columns :

<?php
function array_chunk_fixed($input, $num, $preserve_keys = FALSE) {
    $count = count($input) ;
    if($count)
        $input = array_chunk($input, ceil($count/$num), $preserve_keys) ;
    $input = array_pad($input, $num, array()) ;
    return $input ;
}

$array = array(1, 2, 3, 4, 5) ;
print_r(array_chunk($array, 2)) ;
print_r(array_chunk_fixed($array, 2)) ;
?>

---- array_chunk : fixed number of sub-items ----
Array(
    [0] => Array(
            [0] => 1
            [1] => 2
        )
    [1] => Array(
            [0] => 3
            [1] => 4
        )

    [2] => Array(
            [0] => 5
        )
)

---- array_chunk : fixed number of columns ----
Array(
    [0] => Array(
            [0] => 1
            [1] => 2
            [2] => 3
        )
    [1] => Array(
            [0] => 4
            [1] => 5
        )
)

Mistake key did not do what I thought. A patch.

function array_bucket($array,$bucket_size)// bucket filter
{
    if (!is_array($array)) return false;
    $buckets=array_chunk($array,$bucket_size);// chop up array into bucket size units
    $I=0;
    foreach ($buckets as $bucket)
    {
        $new_array[$I++]=array_sum($bucket)/count($bucket);
    }
    return $new_array;// return new array
}