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  • array_keys()

    (PHP 4, PHP 5, PHP 7)

    返回数组中部分的或所有的键名

    说明

    array_keys(array $array[,mixed $search_value= null[,bool $strict= false]]) : array

    array_keys()返回$input数组中的数字或者字符串的键名。

    如果指定了可选参数$search_value,则只返回该值的键名。否则$input数组中的所有键名都会被返回。

    参数

    $input

    一个数组,包含了要返回的键。

    $search_value

    如果指定了这个参数,只有包含这些值的键才会返回。

    $strict

    判断在搜索的时候是否该使用严格的比较(===)。

    返回值

    返回$input里的所有键。

    范例

    Example #1array_keys()例子

    <?php
    $array = array(0 => 100, "color" => "red");
    print_r(array_keys($array));
    $array = array("blue", "red", "green", "blue", "blue");
    print_r(array_keys($array, "blue"));
    $array = array("color" => array("blue", "red", "green"),
                   "size"  => array("small", "medium", "large"));
    print_r(array_keys($array));
    ?>
    

    以上例程会输出:

    Array
    (
        [0] => 0
        [1] => color
    )
    Array
    (
        [0] => 0
        [1] => 3
        [2] => 4
    )
    Array
    (
        [0] => color
        [1] => size
    )
    

    参见

    It's worth noting that if you have keys that are long integer, such as '329462291595', they will be considered as such on a 64bits system, but will be of type string on a 32 bits system.
    for example:
    <?php 
    $importantKeys = array('329462291595' =>null, 'ZZ291595' => null);
    foreach(array_keys($importantKeys) as $key){
      echo gettype($key)."\n";
    }
    ?>
    will return on a 64 bits system:
    <?php 
      integer
      string
    ?>
    but on a 32 bits system:
    <?php 
      string
      string
    ?>
    I hope it will save someone the huge headache I had :)
    Here's how to get the first key, the last key, the first value or the last value of a (hash) array without explicitly copying nor altering the original array:
    <?php
     $array = array('first'=>'111', 'second'=>'222', 'third'=>'333');
     // get the first key: returns 'first'
     print array_shift(array_keys($array));
     // get the last key: returns 'third'
     print array_pop(array_keys($array));
     // get the first value: returns '111'
     print array_shift(array_values($array));
     // get the last value: returns '333'
     print array_pop(array_values($array));
    ?>
    
    Since 5.4 STRICT standards dictate that you cannot wrap array_keys in a function like array_shift that attempts to reference the array. 
    Invalid:
    echo array_shift( array_keys( array('a' => 'apple') ) );
    Valid:
    $keys = array_keys( array('a' => 'apple') );
    echo array_shift( $keys );
    But Wait! Since PHP (currently) allows you to break a reference by wrapping a variable in parentheses, you can currently use:
    echo array_shift( ( array_keys( array('a' => 'apple') ) ) );
    However I would expect in time the PHP team will modify the rules of parentheses.
    It is worth noting that array_keys does not maintain the data-type of the keys when mapping them to a new array. This created an issue with in_array and doing a lookup on characters from a string. NOTE: my lookup $array has a full map of numbers and characters - upper and lower - to do an simple faux encryption with.
    <?php
    $array = array(
       'e' => 'ieio'
      ,'1' => 'one'
      ,'2' => 'two'
      ,'0' => 'zero'
    );
    var_dump($array);
    $keys = array_keys($array);
    var_dump($keys);
    $string = '1e0';
    for ($i = 0; $i < strlen($string); $i++) {
      if (in_array($string[$i],$keys,'strict')) echo 'dude ';
      else echo 'sweet ';
    }
    ?>
    Outputs:
    array (size=4)
     'e' => string 'ieio' (length=4)
     1 => string 'one' (length=3)
     2 => string 'two' (length=3)
     0 => string 'zero' (length=4)
    array (size=4)
     0 => string 'e' (length=1)
     1 => int 1
     2 => int 2
     3 => int 0
    sweet dude sweet 
    ---- 
    expected to see:
    dude dude dude
    There's a lot of multidimensional array_keys function out there, but each of them only merges all the keys in one flat array.
    Here's a way to find all the keys from a multidimensional array while keeping the array structure. An optional MAXIMUM DEPTH parameter can be set for testing purpose in case of very large arrays.
    NOTE: If the sub element isn't an array, it will be ignore.
    <?php
    function array_keys_recursive($myArray, $MAXDEPTH = INF, $depth = 0, $arrayKeys = array()){
        if($depth < $MAXDEPTH){
          $depth++;
          $keys = array_keys($myArray);
          foreach($keys as $key){
            if(is_array($myArray[$key])){
              $arrayKeys[$key] = array_keys_recursive($myArray[$key], $MAXDEPTH, $depth);
            }
          }
        }
        return $arrayKeys;
      }
    ?>
    EXAMPLE:
    input:
    array(
      'Player' => array(
        'id' => '4',
        'state' => 'active',
      ),
      'LevelSimulation' => array(
        'id' => '1',
        'simulation_id' => '1',
        'level_id' => '1',
        'Level' => array(
          'id' => '1',
          'city_id' => '8',
          'City' => array(
            'id' => '8',
            'class' => 'home',
          )
        )
      ),
      'User' => array(
        'id' => '48',
        'gender' => 'M',
        'group' => 'user',
        'username' => 'Hello'
      )
    )
    output:
    array(
      'Player' => array(),
      'LevelSimulation' => array(
        'Level' => array(
          'City' => array()
        )
      ),
      'User' => array()
    )
    If an array is empty (but defined), or the $search_value is not found in the array, an empty array is returned (not false, null, or -1). This may seem intuitive, especially given the documentation says an array is returned, but I needed to sanity test to be sure:
    <?php
    $emptyArray = array();
    var_dump(array_keys($emptyArray,99)); // array (size=0) \ empty
    $filledArray = array(11,22,33,42);
    var_dump(array_keys($filledArray,99)); // array (size=0) \ empty
    ?>
    
    Sorry for my english...
    I wrote a function to get keys of arrays recursivelly...
    <?php
      function recursive_keys($input, $search_value = null){
        $output = ($search_value !== null ? array_keys($input, $search_value) : array_keys($input)) ;
        foreach($input as $sub){
          if(is_array($sub)){
            $output = ($search_value !== null ? array_merge($output, recursive_keys($sub, $search_value)) : array_merge($output, recursive_keys($sub))) ;
          }
        }
        return $output ;
      }
    ?>
    I hope it will be usefull
    Regards
    An alternative to RQuadling at GMail dot com's array_remove() function:
    <?php
    function array_remove(array $array, $value, $strict=false)
    {
      return array_diff_key($array, array_flip(array_keys($array, $value, $strict)));
    }
    ?>
    
    The position of an element.
    One can apply array_keys twice to get the position of an element from its key. (This is the reverse of the function by cristianDOTzuddas.) E.g., the following may output "yes, we have bananas at position 0".
    <?php
    $a = array("banana" => "yellow", "apple" = "red");
    $k = get_some_fruit();
    if (isset($a[$k]))
    {
      list($pos) = array_keys(array_keys($a), $k);
      print "yes, we have {$k}s at position $pos\n";
    }
    ?>
    Not amazingly efficient, but I see no better alternative.
    Here's a function I needed to collapse an array, in my case from a database query. It takes an array that contains key-value pairs and returns an array where they are actually the key and value.
    <?php
    function array_collapse($arr, $x, $y) {
      $carr = array();
      while ($el = current($arr)) {
        $carr[ $el[$x] ] = $el[$y];
        next($arr);
      }
      return $carr;
    }
    ?>
    Example usage (pseudo-database code):
    <?php
    $query = db_query('SELECT name, value FROM properties');
    $result = db_returnAll($query);
    /* This will return an array like so:
    [
      ['name' -> 'color', 'value' -> 'blue'],
      ['name' -> 'style', 'value' -> 'wide-format'],
      ['name' -> 'weight', 'value' -> 3.6],
      ['name' -> 'name', 'value' -> 'Waerdthing']
    ]
    */
    $propArr = array_collapse($result, 'name', 'value');
    /* Now this array looks like:
    [
      ['color' -> 'blue'],
      ['style' -> 'wide-format'],
      ['weight' -> 3.6],
      ['name' -> 'Waerdthing'],
    */
    ?>
    I found this handy for using with json_encode and am using it for my project http://squidby.com
    might be worth noting in the docs that not all associative (string) keys are a like, output of the follow bit of code demonstrates - might be a handy introduction to automatic typecasting in php for some people (and save a few headaches):
    <?php
    $r = array("0"=>"0","1"=>"1","" =>"2"," "=>"3");
    echo 'how php sees this array: array("0"=>"0","1"=>"1","" =>"2"," "=>"3")',"\n-----------\n";
    var_dump($r); print_r($r); var_export($r);
    echo "\n-----------\n",'var_dump("0","1",""," ") = ',"\n-----------\n";
    var_dump("0","1",""," ");
    ?>
    OUTPUTS:
    how php sees this array: array("0"=>"0","1"=>"1","" =>"2"," "=>"3")
    -----------
    array(4) {
     [0]=>
     string(1) "0"
     [1]=>
     string(1) "1"
     [""]=>
     string(1) "2"
     [" "]=>
     string(1) "3"
    }
    Array
    (
      [0] => 0
      [1] => 1
      [] => 2
      [ ] => 3
    )
    array (
     0 => '0',
     1 => '1',
     '' => '2',
     ' ' => '3',
    )
    -----------
    var_dump("0","1",""," ") =
    -----------
    string(1) "0"
    string(1) "1"
    string(0) ""
    string(1) " "
    [Editor's note: For a complete solution to the printing of complex structures or hashes, see the PEAR::Var_Dump package: http://pear.php.net/package-info.php?pacid=103 , use "pear install Var_Dump" to get it]
    This function will print all the keys of a multidimensional array in html tables.
    It will help to debug when you dont have control of depths.
    <?php
    function show_keys($ar){
      echo "<table width='100%' border='1' bordercolor='#6699CC' cellspacing='0' cellpadding='5'><tr valign='top'>";
       foreach ($ar as $k => $v ) {
         echo "<td align='center' bgcolor='#EEEEEE'>
          <table border='2' cellpadding='3'><tr><td bgcolor='#FFFFFF'><font face='verdana' size='1'>
           " . $k . "
          </font></td></tr></table>";
          if (is_array($ar[$k])) {
           show_keys ($ar[$k]);
         }
         echo "</td>";
       }
      echo "</tr></table>";
    }
    // Multidimensional array ->
    $arvore = array();
    $arvore['1'] = array();
    $arvore['1']['1.1'] = array('1.1.1', '1.1.2', '1.1.3');
    $arvore['1']['1.2'] = array('1.2.1', '1.2.2', '1.2.3');
    $arvore['1']['1.3'] = array('1.3.1', '1.3.2', '1.3.3');
    $arvore['2'] = array();
    $arvore['2']['2.1'] = array('2.1.1', '2.1.2', '2.1.3');
    $arvore['2']['2.2'] = array('2.2.1', '2.2.2', '2.2.3');
    $arvore['2']['2.3'] = array('2.3.1', '2.3.2', '2.3.3');
    $arvore['3'] = array();
    $arvore['3']['3.1'] = array('3.1.1', '3.1.2', '3.1.3');
    $arvore['3']['3.2'] = array('3.2.1', '3.2.2', '3.2.3');
    $arvore['3']['3.3'] = array('3.3.1', '3.3.2'=>array('3.3.2.1', '3.3.2.2'), '3.3.3');
    // <-
    show_keys($arvore);
    ?>
    
    Note, that using array_key_exists() is rather inefficient. The overhead associated with calling a function makes it slower, than using isset($array[$key]), instead of array_key_exists($key, $array)
    using isset() is usually about 1.3 times faster, according to my tests.
    I was looking for a function that simply unset a variable amout of values from a one-dimensional array by key. I ended up with this (returns the array itself if no further parameter than the array is given, false with no params - does not change the source array) 
    usage: array_remove(array $input [, mixed key ...])
    <?php
     function array_remove() {
      if ($stack = func_get_args()) {
       $input = array_shift($stack);
       foreach ($stack as $key) {
        unset($input[$key]);
       }
       return $input;
      }
      return false;
     }
    ?>
    Test:
    <?php
     $a = array('a'=>'fun', 'b'=>3.14, 'sub'=> array('1', '2', '3'), 'd'=>'what', 'e' => 'xample', 5 => 'x');
     print_r($a);
     print_r(array_remove($a, 'd', 'b', 5, 'sub'));
    ?>
    Output: 
    Array
    (
      [a] => fun
      [b] => 3.14
      [sub] => Array
        (
          [0] => 1
          [1] => 2
          [2] => 3
        )
      [d] => what
      [e] => xample
      [5] => x
    )
    Array
    (
      [a] => fun
      [e] => xample
    )
    Hope this helps someone.
    <?php
    /* A Function created by myself for checking multiple array keys
    For Example u got an Array like $_SESSION and u wanna know if the keys 'user','pass','email' and 'type' exists.
    */
    function mKeyChecker($arr,$keys=array()) {
      if(count($keys) > 1) {
        $valid_keys = 0;
        foreach($keys as $key) {
          if(array_key_exists($key,$arr)) $valid_keys++;
        }
        if($valid_keys == count($keys)) {
          return true;
        } else {
          return false;
        }
      } else if(count($keys) == 1) {
        if(array_key_exists($key[0],$arr)) {
          return true;
        } else {
          return false;
        }
      } else {
        return false;
      }
    }
    // Execution Example
    if(mKeyChecker($_SESSION,array('id','user','email','type'))) {
      echo "is!";
    } else {
      echo "not!";  
    }
    ?>
    
    This function will extract keys from a multidimensional array
    <?php
    function multiarray_keys($ar) {
          
      foreach($ar as $k => $v) {
        $keys[] = $k;
        if (is_array($ar[$k]))
          $keys = array_merge($keys, multiarray_keys($ar[$k]));
      }
      return $keys;
    }
    ?>
    Example code:
    <?php
    $array = array("color" => array("1stcolor" => "blue", "2ndcolor" => "red", "3rdcolor" => "green"),
            "size" => array("small", "medium", "large"));
    echo "<pre>";
    print_r($array);
    echo "</pre>";
    echo "<pre>";
    print_r(multiarray_keys($array));
    echo "</pre>";
    ?>
    Example output:
    Array
    (
      [color] => Array
        (
          [1stcolor] => blue
          [2ndcolor] => red
          [3rdcolor] => green
        )
      [size] => Array
        (
          [0] => small
          [1] => medium
          [2] => large
        )
    )
    Array
    (
      [0] => color
      [1] => 1stcolor
      [2] => 2ndcolor
      [3] => 3rdcolor
      [4] => size
      [5] => 0
      [6] => 1
      [7] => 2
    )
    All the cool notes are gone from the site. 
    Here's an example of how to get all the variables passed to your program using the method on this page. This prints them out so you can see what you are doing. 
    <?php
    while (list($key, $value) = each
    (${"HTTP_".$REQUEST_METHOD."_VARS"}))
    {
        echo $key." = ".$value." ";
    }
    ?>
    
    It should be noted that the inverse function to keys (which converts keys to values) is array_count_values (which converts values to keys). This is needed to use things like array_intersect_key. Could go in several places. Took me a while to figure it out.
    Simple ways to prefixing arrays;
    <?php
    function array_keys_prefix($arr, $pref = "") {
      $rarr = array();
      foreach ($arr as $key => $val) {
        $rarr[$pref.$key] = $val;
      }
      return $rarr;
    }
    function array_keys_prefix_multi($arr, $pref = "") {
      $rarr = array();
      foreach ($arr as $key => $val) {
        $rarr[] = array_keys_prefix($val, $pref);
      }
      return $rarr;
    }
    // $a = array("foo" => "FOO", "bar" => "BAR", "baz" => "BAZ"); // or
    $a = array("foo" => "FOO", "bar" => "BAR", "baz" => array(1,2,3));
    print_r(array_keys_prefix($a, "my_"));
    // db fetch...
    $products = array(
      array("id" => 1, "name" => "Foo"),
      array("id" => 2, "name" => "Bar")
    );
    print_r(array_keys_prefix_multi($products, "product_"));
    ?>
    Array
    (
      [my_foo] => FOO
      [my_bar] => BAR
      [my_baz] => Array
        (
          [0] => 1
          [1] => 2
          [2] => 3
        )
    )
    Array
    (
      [0] => Array
        (
          [product_id] => 1
          [product_name] => Foo
        )
      [1] => Array
        (
          [product_id] => 2
          [product_name] => Bar
        )
    )
    I was looking for a function that deletes either integer keys or string keys (needed for my caching).
    As I didn't find a function I came up with my own solution.
    I didn't find the propiest function to post to so I will post it here, hope you find it useful.
    <?php
    function array_extract($array, $extract_type = 1)
    {
      foreach ( $array as $key => $value )
      {
        if ( $extract_type == 1 && is_string($key) )
        {
          // delete string keys
          unset($array[$key]);
        }
        elseif ( $extract_type == 2 && is_int($key) )
        {
          // delete integer keys
          unset($array[$key]);
        }
      }
      return $array;
    }
    ?>
    You can of course define constants to have a nicer look, I have chosen these: EXTR_INT = 1; EXTR_STRING = 2
    EXTR_INT will return an array where keys are only integer while
    EXTR_STRING will return an array where keys are only string
    Have fun with it.
    A nice little trick to get all of the keys who have some type of value:
    $keys = array_keys($array, !null);
    Keys from multi dimensional array to simple array
    Want to traverse an multi dimensional array and get the keys back in a single dimensional array? This will do the trick:
    <?php
      public function array_walk_keys($array, $parentKey = null, &$flattened_array = null)
      {
        if(!is_array($array))
          return $array;
        
        foreach( $array as $key => $val ) {
          $flattenedKeysArray[] = $key;
          
          if(is_array($val))
            array_walk_keys($val, $key, $flattenedKeysArray);
        }
        return $flattenedKeysArray;
      }
    Post By Sven (59892) has to be changed
    $array = array('first'=>'111', 'second'=>'222', 'third'=>'333');
    $rarray = array_keys($array);
    print array_shift($rarray); // first
    print array_pop($rarray); //thrid
    print array_shift($rarray); //second
    print array_pop($rarray); // no result
    Code below is not valid from 5.4.0 
    print array_shift(array_keys($array)); Throws Strict Standards Error
    Sven code works fine till 5.3.29. From 5.4.0 the standards have been changed and results too differ.
    Note :
    Strict Standards : Only variables should be passed by reference
    Please have look of the code in different versions
    http://sandbox.onlinephpfunctions.com/code/24b5fddf14b635f1e37db69a7edffc2cbbed55e1
    http://sandbox.onlinephpfunctions.com/code/f695e8f81e906b4f062b66cf9b3b83b6b620464c
    A needed a function to find the keys which contain part of a string, not equalling a string...
    <?php
    function array_keys_contain($input, $search_value, $strict = false)
      {
        $tmpkeys = array();
        $keys = array_keys($input);
        foreach ($keys as $k)
        {
          if ($strict && strpos($k, $search_value) !== FALSE)
            $tmpkeys[] = $k;
          elseif (!$strict && stripos($k, $search_value) !== FALSE)
            $tmpkeys[] = $k;
        }
        return $tmpkeys;
      }
    ?>
    
    <?php
    /*
     * This function will return the keys of elements in the 
     * haystack where the value is found in array needle
     */
    function array_value_intersect_keys( $array_haystack, $array_needle ){
      $intersected = array_intersect( $array_haystack, $array_needle );
      return array_keys( $intersected );
    }
    // usage 
    $array_haystack = array( 1 => 2, 2 => 5, 'red' => 8, 9 => 14 );
    $array_needle = array( 2, 8 );
    $array_keys_of_intersecting_values = array_value_intersect_keys( $array_haystack, $array_needle );
    print_r( $array_keys_of_intersecting_values );
    ?>
    returns
    Array
    (
      [0] => 1
      [1] => red
    )
    I was trying to figure out how to normalize an array with numerical keys. Since I was doing for() for a lot of things, but only replacing it if the conditions were right, I wound up with off ball arrays I couldn't access. That being said, I looked for a method of normalizing the array and couldn't find one, so I built my own. I'm not sure how to go about making it recursive, but I didn't need that feature for my own, so I just went without recursion.
    //This will take array([5] => "test1", [4] => "test2", [9] => "test3") into array([0] => "test1", [1] => "test2", [2] => "test3") so you can access it easier.
        function normalize_array($array){
         $newarray = array();
         $array_keys = array_keys($array);
         $i=0;
         foreach($array_keys as $key){
          $newarray[$i] = $array[$key];
          
         $i++;
         }
         return $newarray;
        }
    <?php
      //It's a way to get keys from values )
      $es = array("is My FullName"=>"nodar chkuaselidze (nodarinodo)", "You Are" => "I don't know", "Is My Friend" => "ruxadze");
      foreach(array_values($es) as $ess){
        echo $ess." =>";
          
      for($i =0; $i < count(array_keys($es, $ess)); $i++){
          echo reset(array_keys($es, $ess))."<BR>";
        } }
    ?>
    

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