Create 2-element rows from flat array where the every second row value is also the first value of the next row

Question

$arrayinput = array("a", "b", "c", "d", "e");

How can I achieve the following output....

output:

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

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

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

[3] => Array
    (
        [0] => d
        [1] => e
    )

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

)

Answer 1

You can use this, live demo here.

<?php
$arrayinput = array("a","b","c","d","e");

$array = [];
foreach($arrayinput as $v)
{
  $arr = [];
  $arr[] = $v;
  if($next = next($arrayinput))
    $arr[] = $next;
  $array[] = $arr;
}
print_r($array);

Answer 2

live example here: http://sandbox.onlinephpfunctions.com/code/4de9dda457de92abdee6b4aec83b3ccff680334e

$arrayinput = array("a","b","c","d","e");
$result = [];

for ($x = 0; $x < count($arrayinput); $x+=2 ) {
    $tmp = [];
    $tmp[] = $arrayinput[$x];
    if ($x+1 < count($arrayinput)) $tmp[] = $arrayinput[$x+1];
    $result[] = $tmp;
}

var_dump($result);

Answer 3

By declaring single-use reference variables, you don't need to call next() -- which is not falsey-safe and there is a warning in the php manual. You also won't need to keep track of the previous index or make iterated calls of count().

For all iterations except for the first one (because there is no previous value), push the current value into the previous subarray as the second element. After pushing the second value, "disconnect" the reference variable so that the same process can be repeated on subsequent iterations. This is how I'd do it in my own project.

Code: (Demo)

$result = [];
foreach (range('a', 'e') as $value) {
    if ($result) {
        $row[] = $value;
        unset($row);
    }
    $row = [$value];
    $result[] = &$row;
}
var_export($result);

---

If you always want to have 2 elements in each subarray and you want to pad with null on the final iteration, you could use a transposing technique and send a copy of the input array (less the first element) as an additional argument. This is a much more concise technique (one-liner) (Demo)

var_export(array_map(null, $array, array_slice($array, 1)));