array_chunk

(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)

array_chunkSplit an array into chunks

Description

array_chunk(array $array, int $length, bool $preserve_keys = false): array

Chunks an array into arrays with length elements. The last chunk may contain less than length elements.

Parameters

array

The array to work on

length

The size of each chunk

preserve_keys

When set to true keys will be preserved. Default is false which will reindex the chunk numerically

Return Values

Returns a multidimensional numerically indexed array, starting with zero, with each dimension containing length elements.

Errors/Exceptions

If length is less than 1, a ValueError will be thrown.

Changelog

Version Description
8.0.0 If length is less than 1, a ValueError will be thrown now; previously, an error of level E_WARNING has been raised instead, and the function returned null.

Examples

Example #1 array_chunk() example

<?php
$input_array
= array('a', 'b', 'c', 'd', 'e');
print_r(array_chunk($input_array, 2));
print_r(array_chunk($input_array, 2, true));
?>

The above example will output:

Array
(
    [0] => Array
        (
            [0] => a
            [1] => b
        )

    [1] => Array
        (
            [0] => c
            [1] => d
        )

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

)
Array
(
    [0] => Array
        (
            [0] => a
            [1] => b
        )

    [1] => Array
        (
            [2] => c
            [3] => d
        )

    [2] => Array
        (
            [4] => e
        )

)

See Also

add a note

User Contributed Notes 20 notes

up
67
azspot at gmail dot com
17 years ago
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
)

)
up
22
Andrew Martin
6 years ago
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]
?>
up
11
suisuiruyi at aliyun dot com
8 years ago
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]
*/
up
6
dustin at fivetechnology dot com
8 years ago
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;
}
?>
up
19
nate at ruggfamily dot com
13 years ago
If you just want to grab one chunk from an array, you should use array_slice().
up
21
Anonymous
18 years ago
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]
*/
?>
up
8
Anonymous
3 years ago
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]]

?>
up
18
OIS
16 years ago
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
)

)
up
5
siddharthundare at gmail dot com
8 years ago
<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
*/
up
13
phpm at nreynolds dot me dot uk
19 years ago
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;
}

?>
up
6
stratboy
10 years ago
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
?>
up
6
mick at vandermostvanspijk dot nl
20 years ago
[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
$chunks;
}
}
?>
up
8
dead dot screamer at seznam dot cz
15 years ago
This function can be used to reverse effect of <?php array_Chunk()?>.
<?php
function array_Unchunk($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"
}
up
1
leon at valkenb dot org
3 years ago
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;
}
?>
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6
magick dit crow ot gmail dit com
18 years ago
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
}
up
2
normiridium at gmail dot com
8 years ago
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;
up
1
webmaster at cafe-clope dot net
18 years ago
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
)
)
up
-2
magick dit crow ot gmail dit com
18 years ago
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
}
up
-5
Anonymous
10 years ago
Couldn't get the array_chunk_values() working, so ended up with this implementation:

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

$columns = array();
$index = 0;
for (
$i = 0; $i < $num_columns; $i++) {
// Add an extra item to each column while the column number is less than the
// remainder.
$add_rest = ($rest && ($i < $rest)) ? 1 : 0;
$number = $per_column + $add_rest;
$columns[] = array_slice($data, $index, $number);
$index += $number;
}

return
$columns;
}

?>
up
-14
Rasmus Schultz (http://mindplay.dk)
15 years ago
Unfortunately, this function only accepts real arrays, not iterable objects... For that, you need this function:

<?php

function break_array($array, $page_size) {

$arrays = array();
$i = 0;

foreach (
$array as $index => $item) {
if (
$i++ % $page_size == 0) {
$arrays[] = array();
$current = & $arrays[count($arrays)-1];
}
$current[] = $item;
}

return
$arrays;

}

?>
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