(PHP 4, PHP 5)
key — 从关联数组中取得键名
array
该数组。
key() 函数返回数组中内部指针指向的当前单元的键名。
但它不会移动指针。如果内部指针超过了元素列表尾部，或者数组是空的， key() 会返回 NULL。
Example #1 key() 例子
<?php
$array = array(
'fruit1' => 'apple',
'fruit2' => 'orange',
'fruit3' => 'grape',
'fruit4' => 'apple',
'fruit5' => 'apple');
// this cycle echoes all associative array
// key where value equals "apple"
while ($fruit_name = current($array)) {
if ($fruit_name == 'apple') {
echo key($array).'<br />';
}
next($array);
}
?>
以上例程会输出：
fruit1<br /> fruit4<br /> fruit5<br />
B. Keil (2013-05-08 23:19:35)
@FatBat
Your solution is elegant in that it is swift and short - only two commands.
However, performance wise it's not ideal to sort an array to get the key of the highest value. I have written a test case with three examples - yours, another, sophisticated function that allows to pass your own compare function and a third, optimized for performance.
<?php
error_reporting(E_ALL|E_STRICT);
function key_of_max_val(array $array, $cmpFunction = null) {
if ($cmpFunction === null) $cmpFunction = create_function('$a,$b', 'return $a > $b;');
if (!function_exists($cmpFunction)) {
trigger_error(
is_string($cmpFunction) ?
"Did not find function '".mb_substr($cmpFunction, 0, 20)."'" :
"String reference to function expected for \$cmpFunction\n",
E_USER_WARNING
);
return null;
}
$maxKey = key($array);
foreach ($array as $key => $value)
if ($cmpFunction($value, $array[$maxKey]) > 0)
$maxKey = $key;
return $maxKey;
}
function key_of_max_val2(array $array) {
$maxVal = reset($array);
$maxKey = key($array);
foreach ($array as $key => $value) {
if ($value > $maxVal) {
$maxKey = $key;
$maxVal = $value;
}
}
return $maxKey;
}
function key_of_max_val3(array $array) {
arsort($array);
return key($array);
}
$array = array('nadine', 'Natasha', 'Nina', 'nicole');
echo $array[key_of_max_val($array)]."\n";
echo $array[key_of_max_val($array, 'strcasecmp')]."\n";
echo $array[key_of_max_val2($array)]."\n";
echo $array[key_of_max_val3($array)]."\n";
$array = array();
for($i = 0; $i < 1000000; $i++) $array[] = rand(0, 1024*1024);
foreach(array('key_of_max_val', 'key_of_max_val2','key_of_max_val3') as $function) {
$before = microtime(true);
$key = $function($array);
$after = microtime(true);
printf("%s returned key %d referring to %d after %.2f seconds.\n", $function, $key, $array[$key], $after - $before);
}
?>
Results:
$ php example.php
nicole
Nina
nicole
nicole
key_of_max_val returned key 360688 referring to 1048575 after 0.87 seconds.
key_of_max_val2 returned key 360688 referring to 1048575 after 0.16 seconds.
key_of_max_val3 returned key 360688 referring to 1048575 after 1.65 seconds.
However, function 2 has the disadvantage of actually changing the internal array pointer, since it's call-by-reference. If you do that in a foreach loop over $array you're in trouble. Without the reference a typical result is 0.25 seconds.
B. Keil (2013-05-08 12:54:24)
A little warning regarding a trap I fell into:
"foreach()" loops have no effect on the output of this situation. The documentation of "foreach()" says:
"As foreach relies on the internal array pointer changing it within the loop may lead to unexpected behavior. "
Whatever that is supposed to mean, it does not use the internal array pointer in a way that you could read the current position with "key()". The following two loops are NOT equivalent:
<?php
$array = array('a', 'b', 'c');
foreach ($array as $value) {
echo key($array)." => $value\n";
}
echo "\n";
foreach ($array as $key => $value) {
echo "$key => $value\n";
}
?>
Output:
1 => a
1 => b
1 => c
0 => a
1 => b
2 => c
HellFireAE at gmail dot com (2012-03-16 23:37:51)
I've used this as a way of getting $_GET's from the URL. It's actually quite cool, I don't know if this is a hack or what but I like it.
<?php
switch(strToLower(key($_GET))){
case "register":
$page->set("{PAGE_TITLE}", "Register");
break;
default:
$page->set("{PAGE_TITLE}", "Play");
break;
}
?>
So if you put "?register" it outputs the page title to "Register" and if it isn't that, then it's "Play".
Hope this helps people.
goker.cebeci (2012-02-23 19:41:04)
object usage:
<?php
$object = new stdClass();
$object->child->key = 'value';
echo key((array) $object->child);
// key
?>
FatBat (2011-10-17 12:20:49)
Needed to get the index of the max/highest value in an assoc array.
max() only returned the value, no index, so I did this instead.
<?php
reset($x); // optional.
arsort($x);
$key_of_max = key($x); // returns the index.
?>
FokeyJoe (2011-03-10 06:10:50)
Just to illustrate the behaviour of the internal pointer when you add items. Adding to an array does not affect the internal pointer.
<?php
$a = array();
var_dump(key($a)); // null
$a[] = "jump";
var_dump(key($a)); // 0
$a[] = "lazy";
var_dump(key($a)); // 0
end($a);
var_dump(key($a)); // 1
$a[] = "fox";
var_dump(key($a)); // 1
?>
Dallas at ekkysoftware dot com (2010-03-04 21:32:22)
I had a problem when there are nulls in your data, such as:-
<?php
$row = array( 'first'=>'number', 'second'=>'letter', 'third'=>null, 'forth'=>'word');
while($value = current($row)){
echo "\"".key($row)."\"";
next($row);
}
?>
The problem is that current() returns the value 'null', but it isn't the end of the list. To get the correct results I used:-
<?php
foreach($row as $value){
echo "\"".key($row)."\"";
next($row);
}
?>
jamon at clearsightdesign dot com (2009-08-18 22:24:40)
I wrote a simple, yet powerful function for finding a key in an array relative to another key. This is very useful for finding the next key in an associative array if you know the current key, or any other arbitrary key relative to the current key.
This function does not use a foreach loop. I have not tested it for speed compared to a foreach loop. I would assume it's faster since it uses PHP's built in functions, but I could be wrong. I'd appreciate feedback on this.
- Jamon Holmgren
<?php
// array_key_relative - Returns a key in an associative array relative to another key without using foreach. Very useful for finding previous key or finding next key in array, etc
// - Written by Jamon Holmgren (www.jamonholmgren.com). Last revised 8/18/2009. Free for any use.
// function array_key_relative(array $array, string $current_key, int $offset)
function array_key_relative($array, $current_key, $offset = 1) {
// create key map
$keys = array_keys($array);
// find current key
$current_key_index = array_search($current_key, $keys);
// return desired offset, if in array, or false if not
if(isset($keys[$current_key_index + $offset])) {
return $keys[$current_key_index + $offset];
}
return false;
}
?>
Usage example:
<?php
$test_array = array(
"apple" => "Red, shiny fruit",
"orange" => "Orange, dull, juicy fruit",
"pear" => "Usually green and odd-shaped fruit",
"banana" => "Long yellow fruit that monkeys like to eat",
"cantelope" => "Larger than a grapefruit",
"grapefruit" => "Kind of sour"
);
echo array_key_relative($test_array, "apple", 2); // outputs "pear"
echo array_key_relative($test_array, "orange", -1); // outputs "apple" */
$next_key = array_key_relative($test_array, "banana", 1); // Get the key after banana (cantelope)
echo $test_array[$next_key]; // outputs "Larger than a grapefruit"
?>
michael (2008-12-09 11:19:37)
Here is an improved version of the KeyName function below. It is simpler and faster, especially on large arrays as it runs in O(1) instead of O(n).
<?php
function KeyName(array $a, $pos) {
$temp = array_slice($a, $pos, 1, true);
return key($temp);
}
?>
Also, KeyName($a, -1) will return the last key, etc.
Twey (2008-03-15 12:25:21)
As of PHP5, objects are passed by reference by default.
egingell at sisna dot com (2007-12-02 03:12:17)
What's the point of lines 14 and 25? $array is destroyed when the function returns. If you want this to work as written, change line 2 to this: (pass $array by reference instead of by value)
<?
function add_key ($value, &$array) // returns the key of the value added or existing already within the array
?>
> danny at dannymendel dot com
> 12-Apr-2006 09:41
> An auto incremental key value function, returning the key value:
>
> 1 <?
> 2 function add_key ($value, $array) // returns the key of the value added or existing already within the array
> 3 {
> 4 if (is_array ($array))
> 5 {
> 6 if (!in_array ($value, $array))
> 7 {
> 8 ksort ($array);
> 9
>10 end ($array);
>11
>12 $key = key ($array) + 1;
>13
>14 $array[$key] = $value;
>15 }
>16 else
>17 {
>18 $key = array_search ($value, $array);
>19 }
>20 }
>21 else
>22 {
>23 $key = 1;
>24
>25 $array[$key] = $value;
>26 }
>27 return $key;
>28 }
>29 ?>
yarco dot w at gmail dot com (2007-09-13 01:45:42)
Re: br_joris[at]hotmail[doth]com
Do you really mean you want 2 keys point to 1 value?
What you've written seems you want 1 key point to 2 values.
But if you really want 2 keys point to 1 value, you could do the following:
<?php
$buf['key1'] = 'abc';
$buf['key2'] = & $buf['key1'];
?>
danny at dannymendel dot com (2006-04-12 08:41:03)
An auto incremental key value function, returning the key value:
<?
function add_key ($value, $array) // returns the key of the value added or existing already within the array
{
if (is_array ($array))
{
if (!in_array ($value, $array))
{
ksort ($array);
end ($array);
$key = key ($array) + 1;
$array[$key] = $value;
}
else
{
$key = array_search ($value, $array);
}
}
else
{
$key = 1;
$array[$key] = $value;
}
return $key;
}
?>
php_notes at ionws dot com (2005-10-10 16:17:44)
Note that key($array) returns NULL if $array's internal pointer goes past the end of the array. For example, the following code:
<?php
$arr = array(
'one' => '1',
'two' => '2',
'three' => '3',
'four' => '4',
'five' => '5');
for ($i = 0; $i < 10; $i++) {
var_dump(key($arr));
next($arr);
}
?>
results in:
string(3) "one"
string(3) "two"
string(5) "three"
string(4) "four"
string(4) "five"
NULL
NULL
NULL
NULL
NULL
Danniel@t h e - police (d'0't) com (2005-05-22 01:55:36)
To get the key name by position from Array:
<?php
$myArray['name1']=3;
$myArray['name2']=2;
$myArray['name3']=1;
echo($myArray[1]); /* return NULL */
/* isset($myArray[1]) return false; */
/* is_null($myArray[1]) return true; */
function KeyName($myArray,$pos) {
// $pos--;
/* uncomment the above line if you */
/* prefer position to start from 1 */
if ( ($pos < 0) || ( $pos >= count($myArray) ) )
return "NULL"; // set this any way you like
reset($myArray);
for($i = 0;$i < $pos; $i++) next($myArray);
return key($myArray);
}
echo KeyName($myArray,1); // result: name2
echo KeyName($myArray,2); // result: name3
echo KeyName($myArray,3); // result: "NULL"
?>
You can get any existing "key name" from array that is located at position $pos gived as second parameter. If no element is defined at given position the function will return the string "NULL".
Danniel@t h e - police (d'0't) com (2005-05-22 01:55:31)
To get the key name by position from Array:
<?php
$myArray['name1']=3;
$myArray['name2']=2;
$myArray['name3']=1;
echo($myArray[1]); /* return NULL */
/* isset($myArray[1]) return false; */
/* is_null($myArray[1]) return true; */
function KeyName($myArray,$pos) {
// $pos--;
/* uncomment the above line if you */
/* prefer position to start from 1 */
if ( ($pos < 0) || ( $pos >= count($myArray) ) )
return "NULL"; // set this any way you like
reset($myArray);
for($i = 0;$i < $pos; $i++) next($myArray);
return key($myArray);
}
echo KeyName($myArray,1); // result: name2
echo KeyName($myArray,2); // result: name3
echo KeyName($myArray,3); // result: "NULL"
?>
You can get any existing "key name" from array that is located at position $pos gived as second parameter. If no element is defined at given position the function will return the string "NULL".
happy dot machine at skynet dot be (2003-05-06 11:20:04)
<?php
$tab = array();
$tab[0] = 'php';
$tab[1] = '.';
$tab[2] = 'net';
// you will not enter the while
// $key = 0, while will consider $key as false
reset($tab);
while ($key = key($tab) ) {
echo $tab[$key];
next($tab);
}
// this will
reset($tab);
while (!is_null($key = key($tab) ) ) {
echo $tab[$key];
next($tab);
}
// when key() can't return a 'key', it return NULL
echo var_dump($key);
?>
kajetan at kajetan dot nu (2002-07-04 13:20:06)
I'm writing a forum and use an array to hold all the smiles. The keys in the array are the characters to write to get a smiley, and the data is the filename, like this
$Smiles[':-)'] = 'smile.gif'
To output all the smileys in a table with 3 columns, I wrote this code:
<?php
$the_end = false;
$s = reset($Smiles);
$k = key($Smiles);
while(!$the_end){
echo '<tr>';
for($i=0; $i<3; $i++){
echo '<td>';
if($the_end) echo ' ';
else{
echo $k.'< br><img src="'. $s .'">';
$s = next($Smiles);
if ($s==false) $the_end=true;
else
$k = key($Smiles);
}
echo "</td>\n";
}
echo "</tr>\n";
}
?>
I had to write a space in the < br> tag in the code above, because the board did a line brake otherwise.
mkeller at gmx dot de (2001-10-11 12:46:41)
In the case key() does not give you back the key(myarray) but "0", try this:
(Try this example without the line containing "end($myarray)" and you see my reason for this post...)
<?php
for($i = 0; $i <= 10; $i++) {
$myarray[] = 'content '.$i;
end($myarray);
echo ('<br>key()='.key($myarray).' , content='.$myarray[$i]);
}
?>
php at snr-graphics dot com (2001-03-23 11:50:25)
A Method of Multi-Dimensionalizing an Associative Array (This idea was designed with Graphics (image filenames in mind):
(A quick overview):
While working on a rather large web application, I found that I needed a way to obtain "all" the details on images used by the application, these images (by filename) were stored in the configuration file, in the form of associative arrays.
The following represents an example of how I tool those and converted them into multi-dimensional associative arrays.
<?php
do {
$size = getImageSize($path.$myarray[key($myarray)]);
if ($size[2] == '1') { $size[2] = 'gif'; }
else if ($size[2] == '2') { $size[2] = 'jpg'; }
else if ($size[2] == '3') { $size[2] = 'png'; }
else if ($size[2] == '4') { $size[2] = 'swf'; }
else { $size[2] = 'UNKNOWN'; }
$myarray[key($myarray)] = Array($myarray[Key($myarray)],$size[0],$size[1],$size[2],$size[3]);
} while (next($myarray));
?>
The end result is an multi-dim. associative array which contains the values:
<?php
$myarray["this"][0] = # filename.gif
$myarray["this"][1] = # width
$myarray["this"][2] = # height
$myarray["this"][3] = # type (converted to the file extension.)
$myarray["this"][4] = # height=x width=x
?>
This may not be all that impressive to some, but it turned out to be very useful for me, so I thought I'd share, in addition, I think it gives a "very" good example of "a use" for the Key() function.
Frankly, I was quite happy to discover this function, I can't count the number of times I "needed to use the key as a value".
I hope you find this code useful.