对于第一个数组，使用array_splice():

$array_1 = array(
  '0' => 'zero',
  '1' => 'one',
  '2' => 'two',
  '3' => 'three',
);

array_splice($array_1, 3, 0, 'more');
print_r($array_1);

输出:

Array(
    [0] => zero
    [1] => one
    [2] => two
    [3] => more
    [4] => three
)

对于第二个，没有顺序，所以你只需要做:

$array_2['more'] = '2.5';
print_r($array_2);

把钥匙按你想要的排序。

我最近写了一个函数来做一些类似于你正在尝试的事情，这与clasvdb的答案类似。

function magic_insert($index,$value,$input_array ) {
  if (isset($input_array[$index])) {
    $output_array = array($index=>$value);
    foreach($input_array as $k=>$v) {
      if ($k<$index) {
        $output_array[$k] = $v;
      } else {
        if (isset($output_array[$k]) ) {
          $output_array[$k+1] = $v;
        } else {
          $output_array[$k] = $v;
        }
      } 
    }

  } else {
    $output_array = $input_array;
    $output_array[$index] = $value;
  }
  ksort($output_array);
  return $output_array;
}

基本上，它在一个特定的点插入，但通过向下移动所有项来避免覆盖。

更简洁的方法(基于使用的流动性和更少的代码)。

/**
 * Insert data at position given the target key.
 *
 * @param array $array
 * @param mixed $target_key
 * @param mixed $insert_key
 * @param mixed $insert_val
 * @param bool $insert_after
 * @param bool $append_on_fail
 * @param array $out
 * @return array
 */
function array_insert(
    array $array, 
    $target_key, 
    $insert_key, 
    $insert_val = null,
    $insert_after = true,
    $append_on_fail = false,
    $out = [])
{
    foreach ($array as $key => $value) {
        if ($insert_after) $out[$key] = $value;
        if ($key == $target_key) $out[$insert_key] = $insert_val;
        if (!$insert_after) $out[$key] = $value;
    }

    if (!isset($array[$target_key]) && $append_on_fail) {
        $out[$insert_key] = $insert_val;
    }

    return $out;
}

用法:

$colors = [
    'blue' => 'Blue',
    'green' => 'Green',
    'orange' => 'Orange',
];

$colors = array_insert($colors, 'blue', 'pink', 'Pink');

die(var_dump($colors));

如果你只是想在数组的某个位置插入一个项(基于@clausvdb的答案):

function array_insert($arr, $insert, $position) {
    $i = 0;
    $ret = array();
    foreach ($arr as $key => $value) {
            if ($i == $position) {
                $ret[] = $insert;
            }
            $ret[] = $value;
            $i++;
    }
    return $ret;
}

该函数支持:

数字键和关联键 在建立键之前或之后插入 如果key未建立，则附加到数组末尾

function insert_into_array( $array, $search_key, $insert_key, $insert_value, $insert_after_founded_key = true, $append_if_not_found = false ) {

        $new_array = array();

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

            // INSERT BEFORE THE CURRENT KEY? 
            // ONLY IF CURRENT KEY IS THE KEY WE ARE SEARCHING FOR, AND WE WANT TO INSERT BEFORE THAT FOUNDED KEY
            if( $key === $search_key && ! $insert_after_founded_key )
                $new_array[ $insert_key ] = $insert_value;

            // COPY THE CURRENT KEY/VALUE FROM OLD ARRAY TO A NEW ARRAY
            $new_array[ $key ] = $value;

            // INSERT AFTER THE CURRENT KEY? 
            // ONLY IF CURRENT KEY IS THE KEY WE ARE SEARCHING FOR, AND WE WANT TO INSERT AFTER THAT FOUNDED KEY
            if( $key === $search_key && $insert_after_founded_key )
                $new_array[ $insert_key ] = $insert_value;

        }

        // APPEND IF KEY ISNT FOUNDED
        if( $append_if_not_found && count( $array ) == count( $new_array ) )
            $new_array[ $insert_key ] = $insert_value;

        return $new_array;

    }

用法:

    $array1 = array(
        0 => 'zero',
        1 => 'one',
        2 => 'two',
        3 => 'three',
        4 => 'four'
    );

    $array2 = array(
        'zero'  => '# 0',
        'one'   => '# 1',
        'two'   => '# 2',
        'three' => '# 3',
        'four'  => '# 4'
    );

    $array3 = array(
        0 => 'zero',
        1 => 'one',
       64 => '64',
        3 => 'three',
        4 => 'four'
    );


    // INSERT AFTER WITH NUMERIC KEYS
    print_r( insert_into_array( $array1, 3, 'three+', 'three+ value') );

    // INSERT AFTER WITH ASSOC KEYS
    print_r( insert_into_array( $array2, 'three', 'three+', 'three+ value') );

    // INSERT BEFORE
    print_r( insert_into_array( $array3, 64, 'before-64', 'before-64 value', false) );

    // APPEND IF SEARCH KEY ISNT FOUNDED
    print_r( insert_into_array( $array3, 'undefined assoc key', 'new key', 'new value', true, true) );

结果:

Array
(
    [0] => zero
    [1] => one
    [2] => two
    [3] => three
    [three+] => three+ value
    [4] => four
)
Array
(
    [zero] => # 0
    [one] => # 1
    [two] => # 2
    [three] => # 3
    [three+] => three+ value
    [four] => # 4
)
Array
(
    [0] => zero
    [1] => one
    [before-64] => before-64 value
    [64] => 64
    [3] => three
    [4] => four
)
Array
(
    [0] => zero
    [1] => one
    [64] => 64
    [3] => three
    [4] => four
    [new key] => new value
)

使用array_splice而不是array_slice可以减少一次函数调用。

$toto =  array(
  'zero'  => '0',
  'one'   => '1',
  'two'   => '2',
  'three' => '3'
);
$ret = array_splice($toto, 3 );
$toto = $toto +  array("my_key" => "my_value") + $ret;
print_r($toto);