PHP use of array_map array_shift to slice array into odd and even sub arrays

Question

By definition, PHP's array_shift will return the first elem from the array and the array will downsize one.

I want to slice an array alternatingly into two sub-arrays, i.e index of 0,2,4,6,... and index of 1,3,5,7,...

I first break it into chunks of 2, then I use array_map to call array_shift. However, it is half correct (output below):

array1: Array ( [0] => greeting [1] => question [2] => response ) 
array2: Array ( [0] => Array ( [0] => greeting [1] => hello ) [1] => Array ( [0] => question [1] => how-are-you ) [2] => Array ( [0] => response [1] => im-fine ) )

Here's the code:

$a=array("greeting", "hello", "question", "how-are-you", "response", "im-fine");
$b=array_chunk($a, 2);
$c=array_map("array_shift", $b);
echo "array1: ";
print_r($c);
echo "array2: ";
print_r($b);

array2 does not seem to downsize after array_shift. Is this the correct behavior? How can I do what I intend to do?

Thanks

possible duplicate of Split array into two arrays by index even or odd — MrMarlow
– MrMarlow, Commented Jan 18, 2015 at 3:15

A Smith · Accepted Answer · 2015-07-19 12:36:31Z

0

While this is already solved using array functions here is a low tech solution using a simple toggle to separate the odd and even elements...

$in = array("greeting", "hello", "question", "how-are-you", "response", "im-fine");

$i = 0;
$list = array();
foreach ($in as $text)
{
  $list[$i][] = $text;
  $i = 1 - $i;
}

print_r($list[0]);
print_r($list[1]);

Result...

Array ( [0] => greeting [1] => question [2] => response ) 
Array ( [0] => hello [1] => how-are-you [2] => im-fine )

edited Jul 19, 2015 at 12:36

answered Jul 19, 2015 at 12:31

A Smith

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A l w a y s S u n n y · Accepted Answer · 2015-01-18 03:31:03Z

-2

Try this way to split your array alternatively EVEN and ODD keys, there may be many ways to do this, but this is my simple way using array_walk

$odd = [];
$even = [];
$both = [&$even, &$odd];
$array=["greeting", "hello", "question", "how-are-you", "response", "im-fine"];
array_walk($array, function($value, $key) use ($both) { $both[$key % 2][] = $value; });
print '<pre>';
print_r($even);
print_r($odd);
print '</pre>';

RESULT: Success time: 0.02 memory: 24448 signal:0

<pre>Array
(
    [0] => greeting
    [1] => question
    [2] => response
)
Array
(
    [0] => hello
    [1] => how-are-you
    [2] => im-fine
)

edited Jan 18, 2015 at 3:31

answered Jan 17, 2015 at 3:26

A l w a y s S u n n y

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4 Comments

Shuang Liang Over a year ago

Hi, Being Human: Thanks for the suggestions. The first works and the second prints out like this: Array ( ) Array ( )

A l w a y s S u n n y Over a year ago

@ShuangLiang see my edited answer, as i set $array variable in my first solution, so it was not set here, that's why you get Array(), check now...

MrMarlow Over a year ago

Credit where credit is due; stackoverflow.com/questions/12405264/…

Shuang Liang Over a year ago

@Being Human I see there is one way left. One way or the other, it counts as long as it works. Thanks.

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