array_combine()

(PHP 5, PHP 7)

创建一个数组，用一个数组的值作为其键名，另一个数组的值作为其值

说明

array_combine(array $keys,array $values): array

返回一个array，用来自$keys数组的值作为键名，来自$values数组的值作为相应的值。

参数

$keys: 将被作为新数组的键。非法的值将会被转换为字符串类型（string）。
$values: 将被作为Array的值。

返回值

返回合并的array，如果两个数组的单元数不同则返回FALSE。

错误／异常

如果作为$keys的数组和作为$values的数组的元素个数不一样，将会抛出一个警告错误（E_WARNING）。

更新日志

版本	说明
5.4.0	（修复）早期版本中如果是空数组就报`E_WARNING`的错并且返回`FALSE`。

范例

一个array_combine()简单的例子

<?php
$a = array('green', 'red', 'yellow');
$b = array('avocado', 'apple', 'banana');
$c = array_combine($a, $b);
print_r($c);
?>

以上例程会输出：

Array
(
    [green]  => avocado
    [red]    => apple
    [yellow] => banana
)

参见

array_merge() 合并一个或多个数组
array_walk() 使用用户自定义函数对数组中的每个元素做回调处理
array_values() 返回数组中所有的值

If two keys are the same, the second one prevails. 
Example:
<?php
print_r(array_combine(Array('a','a','b'), Array(1,2,3)));
?>
Returns:
Array
(
  [a] => 2
  [b] => 3
)
But if you need to keep all values, you can use the function below:
<?php
function array_combine_($keys, $values)
{
  $result = array();
  foreach ($keys as $i => $k) {
    $result[$k][] = $values[$i];
  }
  array_walk($result, create_function('&$v', '$v = (count($v) == 1)? array_pop($v): $v;'));
  return  $result;
}
print_r(array_combine_(Array('a','a','b'), Array(1,2,3)));
?>
Returns:
Array
(
  [a] => Array
    (
      [0] => 1
      [1] => 2
    )
  [b] => 3
)

Further to loreiorg's script 
in order to preserve duplicate keys when combining arrays.
I have modified the script to use a closure instead of create_function
Reason: see security issue flagged up in the documentation concerning create_function
<?php
function array_combine_($keys, $values){
  $result = array();
  foreach ($keys as $i => $k) {
   $result[$k][] = $values[$i];
   }
  array_walk($result, function(&$v){
   $v = (count($v) == 1) ? array_pop($v): $v;
   });
  return $result;
}
?>

array_combine() has a strange bug/misfeature (as of PHP 5.3.2): There is no logical reason for <? array_combine(array(), array()) ?> throwing a warning and returning FALSE, instead of returning <? array() ?> (see http://bugs.php.net/bug.php?id=34857). Here is a quick workaround:
<?php
function array_real_combine($a, $b)
{
  return $a===array() && $b===array() ? array() : array_combine($a, $b);
}
?>

<?php
// If they are not of same size, here is solution:
$abbreviations = array("AL", "AK", "AZ", "AR", "TX", "CA");
$states = array("Alabama", "Alaska", "Arizona", "Arkansas");
function combine_arr($a, $b)
{
  $acount = count($a);
  $bcount = count($b);
  $size = ($acount > $bcount) ? $bcount : $acount;
  $a = array_slice($a, 0, $size);
  $b = array_slice($b, 0, $size);
  return array_combine($a, $b);
}
$combined = combine_arr($abbreviations, $states);
print_r($combined); 
// Output
// Array ( [AL] => Alabama [AK] => Alaska [AZ] => Arizona 
// [AR] => Arkansas )
?>

I recently had to flip an array and group the elements by value, this snippet will do that:
<?php
function flipAndGroup($input) {
  $outArr = array();
  array_walk($input, function($value, $key) use (&$outArr) {
    if(!isset($outArr[$value]) || !is_array($outArr[$value])) {
      $outArr[$value] = [];
    }
    $outArr[$value][] = $key;
  });
  return $outArr;
}
?>
Example:
<?php
$users_countries = array(
  'username1' => 'US',
  'user2' => 'US',
  'newuser' => 'GB'
);
print_r(flipAndGroup($users_countries));
?>
Returns:
Array
(
  [US] => Array
    (
      [0] => username1
      [1] => user2
    )
  [GB] => Array
    (
      [0] => newuser
    )
)

I needed to read CSV files into associative arrays with column headers as keys. Then I ran into a problem when you have empty columns at the end of a row because array_combine returns false if both arrays don't have the same number of elements. This function based on quecoder at gmail's combine_arr() below allowed me to pad either array or not when parsing my CSVs to arrays.
$a is the array of header columns and $b is an array of the current row retrieved with fgetcsv()
<?php
function array_combine_special($a, $b, $pad = TRUE) {
  $acount = count($a);
  $bcount = count($b);
  // more elements in $a than $b but we don't want to pad either
  if (!$pad) {
    $size = ($acount > $bcount) ? $bcount : $acount;
    $a = array_slice($a, 0, $size);
    $b = array_slice($b, 0, $size);
  } else {
    // more headers than row fields
    if ($acount > $bcount) {
      $more = $acount - $bcount;
      // how many fields are we missing at the end of the second array?
      // Add empty strings to ensure arrays $a and $b have same number of elements
      $more = $acount - $bcount;
      for($i = 0; $i < $more; $i++) {
        $b[] = "";
      }
    // more fields than headers
    } else if ($acount < $bcount) {
      $more = $bcount - $acount;
      // fewer elements in the first array, add extra keys    
      for($i = 0; $i < $more; $i++) {
        $key = 'extra_field_0' . $i;
        $a[] = $key;
      }
      
    }
  }
  
  return array_combine($a, $b);
}
?>

If two keys are the same, the second one prevails.
Example:
<?php
print_r(array_combine(Array('a','a','b'), Array(1,2,3)));
?>
Returns:
Array
(
  [a] => 2
  [b] => 3
)

This will seem obvious to some, but if you need to preserve a duplicate key, being you have unique vars, you can switch the array_combine around, to where the vars are the keys, and this will output correctly.
This [default] formula auto-removes the duplicate keys.
$i=0;
foreach (array_combine($keys, $vars) as $key => $var)
{
$i=$i;
echo($key);
echo " ";
echo($var);
}
This formula accomplishes the same thing, in the same order, but the duplicate "keys" (which are now vars) are kept.
$i=0;
foreach (array_combine($vars, $keys) as $var => $key)
{
$i=$i;
echo($key);
echo " ";
echo($var);
}
I know, I'm a newbie, but perhaps someone else will need this eventually. I couldn't find another solution anywhere.

I needed a function that truncated extra values, and only went as far as keys without throwing a warning as array_combine does.
<?php
function safeArrayCombine($keys, $values) {
  $combinedArray = array();
    
  for ($i=0, $keyCount = count($keys); $i < $keyCount; $i++) {
     $combinedArray[$keys[$i]] = $values[$i];
  }
    
  return $combinedArray;
}
?>

I needed a function that would take keys from one unequal array and combine them with the values of another. Real life application:
Select 4 product types.
Each product has a serial.
There are 4 sets of products.
  <?php
    function array_combine2($arr1, $arr2) {
      $count1 = count($arr1);
      $count2 = count($arr2);
      $numofloops = $count2/$count1;
        
      $i = 0;
      while($i < $numofloops){
        $arr3 = array_slice($arr2, $count1*$i, $count1);
        $arr4[] = array_combine($arr1,$arr3);
        $i++;
      }
      
      return $arr4;
    }
  ?>
Input:
Array
(
  [0] => SMART Board
  [1] => Projector
  [2] => Speakers
  [3] => Splitter
)
, Array
(
  [0] => serial to smart board1
  [1] => serial to projector 1
  [2] => serial to speakers 1
  [3] => serials to splitter 1
  [4] => serials to smart board 2
  [5] => serials to projector 2
  [6] => serials to speakers 2
  [7] => serials to splitter 2
)
Array
(
  [0] => Array
    (
      [SMART Board] => serial to smart board1
      [Projector] => serial to projector 1
      [Speakers] => serial to speakers 1
      [Splitter] => serials to splitter 1
    )
  [1] => Array
    (
      [SMART Board] => serials to smart board 2
      [Projector] => serials to projector 2
      [Speakers] => serials to speakers 2
      [Splitter] => serials to splitter 2
    )
)

I had an epiphany when try to handle NON-ASSOCIATIVE array forms in my controller. This little one liner can pretty much edit ANY kind of non-associative array. For example this one just returns an array of values inputed by a new user.
The $data value is the the json_decoded() value of a register form.
Here is used str_replace, you could definitely do a number of things like preg matches and other things. 
$readyToProcessForUser = array_combine(str_replace("new_user_", "", array_keys($data)), $data);
You could also do the same for the values.
$readyToProcessForUser = array_combine(array_keys($data), str_replace("-", "", $data));
Or BOTH!
Use full if you don't want to walk an entire array and the keys through the same callback.
$readyToProcessForUser = array_combine(array_walk('trim', array_keys($data)), array_walk('custom_callback', array_values($data)));

$item = array();
array_map(
  function($element) use($column_name,$key,&$item){
    $item[$element[$key]] = $element[$column_name];
  },
  $data
);

This is the function for PHP4 :
<?php
function array_combine($arr1,$arr2) {
  $out = array();
  foreach($arr1 as $key1 => $value1)  {
  $out[$value1] = $arr2[$key1];
  }
  return $out
}
?>

I was looking for a function that could combine an array to multiple one, for my MySQL GROUP_CONCAT() query, so I made this function.
<?php
  function array_combine_array(array $keys)
  {
    $arrays = func_get_args();
    $keys = array_shift($arrays);
    
    /* Checking if arrays are on the same model (array('INDEX'=> array()) or array()) */
    $check = count(array_unique(array_map('is_array',array_map('current',$arrays)))) === 1;
    if (!$check) { trigger_error('Function array_combine_array() expects all parameters to be same type array or array of array',E_USER_NOTICE); return array(); }
    
    /* Checking the model of arrays, array('INDEX' => array()) or Array() */
    $assocArray = is_array(array_shift(array_map('current',$arrays)));
    
    /* If empty $Keys is given, we fill an empty array */
    if (empty($keys)) $keys = array_keys(array_fill(0,max(($assocArray) ? array_map('count',array_map('current',$arrays)) : array_map('count',$arrays)),'foo'));
    /* Init */
    $ret=array();$i=0;
    /* Cycling on each keys values, making an offset for each */
    foreach($keys as $v)
    {
      /* Cycling on arrays */
      foreach ($arrays as $k)
      {
        if ($assocArray)
        {
          /* Getting the index of the element */
          $key = key($k);
          /* If the offset exists, we place it */
          $ret[$v][$key] = isset($k[$key][$i]) ? $k[$key][$i]:false;
        }
        /* Making the array with auto-made index */
        else
          $ret[$v][] = isset($k[$i]) ? $k[$i]: false;
      }
      /* Getting the next offset */
      $i++;
    }
    return $ret;
  }
  /* Examples */
  $r = array(1,2,4,10);
  $a1 = array('one','two','four','ten');
  $a2 = array('un','deux','quatre','dix');
  $a3 = array('uno','dos','quatro','diez');
   
   print_r(array_combine_array($r,array('english' => $a1),array('french' => $a2),array('spanish' => $a3))); /* Associative index, associative subarray indexes */
   print_r(array_combine_array($r,$a1,array('french' => $a2),array('spanish' => $a3))); /* Ouputs Error */
   print_r(array_combine_array($r,$a1,$a2,$a3)); /* Associative index, auto-made subarray indexes */
   print_r(array_combine_array(array(),array('english' => $a1),array('french' => $a2),array('spanish' => $a3))); /* Auto-made index, associative subarray indexes */
?>

Some tips for merging same values in an array
<?php
$array1 = array(1,2,3,4,5,6,7,8,9,10,11,12);
$array2 = array(1,2,3,13);
$merged = array_merge($array1,$array2);
// output normal array_merge
echo '<pre>After array_merge :
';
print_r($merged);
echo '</pre>';
// do double flip for merging values in an array
$merged = array_flip($merged);
$merged = array_flip($merged);
// Output after
echo '<pre>After Double Flip : 
';
print_r($merged);
echo '</pre>';
?>
Output ::
After array_merge :
Array
(
  [0] => 1
  [1] => 2
  [2] => 3
  [3] => 4
  [4] => 5
  [5] => 6
  [6] => 7
  [7] => 8
  [8] => 9
  [9] => 10
  [10] => 11
  [11] => 12
  [12] => 1
  [13] => 2
  [14] => 3
  [15] => 13
)
After Double Flip : 
Array
(
  [12] => 1
  [13] => 2
  [14] => 3
  [3] => 4
  [4] => 5
  [5] => 6
  [6] => 7
  [7] => 8
  [8] => 9
  [9] => 10
  [10] => 11
  [11] => 12
  [15] => 13
)

Khaly's PHP4 code below does not work correctly in all cases. Consider when your array consists of floats:
<?php
$okay = array(0, 10, 20, 30);
$not_okay = array(0, 0.5, 1, 1.5);
$foo = array_combine($okay, $okay);
$bar = array_combine($not_okay, $not_okay);
/* 
Results:
$foo = {
 [0]=> int(0)
 [10]=> int(10)
 [20]=> int(20)
 [30]=> int(30)
}
$bar = {
 [0]=> float(0.5)
 [1]=> float(1.5)
}
*/
?>
What can you do? In my case, I was just zipping up some select-box options, so I converted everything in my floats to strings.

Function eliminates the error Throws E_WARNING if the number of elements in keys and values does not match.
function arrCombine($arr1 = array(),$arr2 = array()){
      if(is_array($arr1) && is_array($arr2)):
        $cntArr1 = count($arr1);
        $cntArr2 = count($arr2);
        $difference = max($cntArr1,$cntArr2) - min($cntArr1,$cntArr2);
        if($cntArr1 > $cntArr2):
          for ($i=1;$i<=$difference;$i++){
            $arr2[$cntArr2+$i] = $cntArr2 + 1;
          }
          return array_combine($arr1,$arr2);
        elseif($cntArr1 < $cntArr2):
          for ($i=1;$i<=$difference;$i++){
            $arr1[$cntArr1+$i] = count($arr1) + 1;
          }
          return array_combine($arr1,$arr2);
        else:
          return array_combine($arr1,$arr2);
        endif;
      endif;
  }
$array = [1,4,5,6,7,8];
$array2 = ['john','smith'];
var_dump( arrCombine($array,$array2 ));
array (size=6)
 1 => string 'john' (length=4)
 4 => string 'smith' (length=5)
 5 => int 3
 6 => int 3
 7 => int 3
 8 => int 3
var_dump( arrCombine($array2,$array) );
array (size=6)
 'john' => int 1
 'smith' => int 4
 3 => int 5
 4 => int 6
 5 => int 7
 6 => int 8

You can create an array hashset from a flat array, storing both keys and values, with array_combine(). This works with duplicate values in the array too.
<?php
$flat_array = array(
    'one',
    'two',
    'three',
    'three',
    'four',
    'one'
);
$set = array_combine($flat_array, $flat_array);
var_dump($set);
?>
This outputs the following:
array(4) {
  ["one"]=>
    string(3) "one"
  ["two"]=>
    string(3) "two"
  ["three"]=>
    string(5) "three"
  ["four"]=>
    string(4) "four"
}

<?php
/**
 * Return alternatives defined by values of each parameters.
 *
 * Exemple :
 *
 * array_alternatives(array('foo','bar'), array('baz', 'qux'));
 * array(
 *   array('foo', 'baz'),
 *   array('bar', 'baz'),
 *   array('foo', 'qux'),
 *   array('bar', 'qux'),
 * );
 * 
 * array_alternatives(array('a'), array('simple-minded'), array('solution'));
 * array(
 *   array('a', 'simple-minded', 'solution')
 * );
 * 
 * array_alternatives(array('a'), array('red', 'blue'), array('car'));
 * array(
 *   array('a', 'red', 'car'),
 *   array('a', 'blue', 'car'),
 * );
 * 
 * @param array $first_element
 * @param array $second_element
 * @return array
 * @author Xavier Barbosa
 */
function array_alternatives(array $first_element, array $second_element)
{
  $lists = func_get_args();
  $total_lists = func_num_args();
  
  for($i=0; $i<$total_lists; $i++)
  {
    $list =& $lists[$i];
    if (is_array($list) === FALSE)
      throw new Exception("Parameter $i is not an array.");
    if (count($list) === 0)
      throw new Exception("Parameter $i has no element.");
    unset($list);
  }
  
  // Initialize our alternatives
  $alternatives = array();
  foreach($lists[0] as &$value)
  {
    array_push($alternatives, array($value));
    unset($value);
  }
  unset($lists[0]);
  
  // Process alternatives
  for($i=1; $i<$total_lists; $i++)
  {
    $list =& $lists[$i];
    
    $new_alternatives = array();
    foreach($list as &$value)
    {
      foreach($alternatives as $_)
      {
        array_push($_, $value);
        array_push($new_alternatives, $_);
      }
    }
    
    // Rotate references, it's cheaper than copy array like `$alternatives = $new_alternatives;`
    $alternatives =& $new_alternatives;
    unset($new_alternatives, $list, $lists[$i]);
  }
  
  return $alternatives;
}
?>

This may be obvious, but I don't see anything about it on the manual page, so a friendly warning... The array you are using as keys must have all unique values. If not, array elements get dropped. 
<?php
$arr_notUnique = array('one' , 'one' , 'two');
$arr_b = array('red' , 'green' , 'blue');
$arr_combo = array_combine($arr_notUnique, $arr_b);
?>
Results: Array ( [one] => green [two] => blue )
NOT: Array ( [one] => red [one] => green [two] => blue )

array_combine() returns NULL instrad of FALSE, when non-array parameters are given (issuing warning).
<?php
 //NULL
 var_dump(array_combine('string',array(42)));
?>