php数组算法有问题

Question

I'm not good at algorithm. Here is my trouble.

I have an array:

$test_arr = array(
  0 => 'a',
  1 => 'b',
  2 => 'c',
  3 => 'd',
  4 => 'e',
  5 => 'f',
  6 => 'g',
  7 => 'h',
  8 => 'i',
);

How do i reorder it with some algorithms like this:

$test_arr = array(
  0 => array(
    'a', 'b',
  ),
  1 => array(
    'c', 'd',
  ),
  2 => array(
    'e', 'f'
  ),
  3 => array(
    'g', 'h',
  ),
  4 => array(
    'i',
  ),
);

Thanks in advance!

Answer 1

PHP already has a builtin function to do exactly the same task. That is array_chunk()

Try this:

<?php
$test_arr = array(
0 => 'a',
1 => 'b',
2 => 'c',
3 => 'd',
4 => 'e',
5 => 'f',
6 => 'g',
7 => 'h',
8 => 'i',
);
var_dump(array_chunk($test_arr, 2));
?>

Answer 2

Here is algorithm you are looking for:

$test_arr = array(
  0 => 'a',
  1 => 'b',
  2 => 'c',
  3 => 'd',
  4 => 'e',
  5 => 'f',
  6 => 'g',
  7 => 'h',
  8 => 'i',
);

$tmp_array = [];
$new_array = [];
$i = 1;
foreach($test_arr as $k => $v){
    if($i % 2 == 0){
        $tmp_array[] = $v;
        $new_array[] = $tmp_array;
        $tmp_array = [];
    }else{
        $tmp_array[] = $v;
    }

    $i++;
}
if(count($tmp_array) > 0){
    $new_array[] = $tmp_array;
}


echo '<pre>';
print_r($new_array);

Answer 3

This solution loops through the given array and saves current and next values to a new array ONLY if the current key is either 0 or an even number.

<?php
$test_arr = array(
  0 => 'a',
  1 => 'b',
  2 => 'c',
  3 => 'd',
  4 => 'e',
  5 => 'f',
  6 => 'g',
  7 => 'h',
  8 => 'i',
);
$newarray = array();
foreach( $test_arr as $key => $value){
    if ( ($key == 0) || (($key % 2) == 0)){ 
        if( isset($test_arr[($key + 1)]) ) { $next = $test_arr[($key + 1)]; } else { $next = ''; }
        $newarray[] = array($value,  $next);
    }
}
echo print_r($newarray, true);
?>

Result

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

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

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

    [3] => Array
        (
            [0] => g
            [1] => h
        )

    [4] => Array
        (
            [0] => i
            [1] => 
        )

)