Php array key value index
// Before php 5.4
$array = array(1,2,3);
// since php 5.4 , short syntax
$array = [1,2,3];
// I recommend using the short syntax if you have php version >= 5.4
Used to creating arrays like this in Perl?
Looks like we need the range() function in PHP:
$array = array_merge (array( ‘All’ ), range ( ‘A’ , ‘Z’ ));
?>
You don’t need to array_merge if it’s just one range:
There is another kind of array (php>= 5.3.0) produced by
$array = new SplFixedArray(5);
Standard arrays, as documented here, are marvellously flexible and, due to the underlying hashtable, extremely fast for certain kinds of lookup operation.
Supposing a large string-keyed array
$arr=[‘string1’=>$data1, ‘string2’=>$data2 etc. ]
when getting the keyed data with
php does *not* have to search through the array comparing each key string to the given key (‘string1’) one by one, which could take a long time with a large array. Instead the hashtable means that php takes the given key string and computes from it the memory location of the keyed data, and then instantly retrieves the data. Marvellous! And so quick. And no need to know anything about hashtables as it’s all hidden away.
However, there is a lot of overhead in that. It uses lots of memory, as hashtables tend to (also nearly doubling on a 64bit server), and should be significantly slower for integer keyed arrays than old-fashioned (non-hashtable) integer-keyed arrays. For that see more on SplFixedArray :
Unlike a standard php (hashtabled) array, if you lookup by integer then the integer itself denotes the memory location of the data, no hashtable computation on the integer key needed. This is much quicker. It’s also quicker to build the array compared to the complex operations needed for hashtables. And it uses a lot less memory as there is no hashtable data structure. This is really an optimisation decision, but in some cases of large integer keyed arrays it may significantly reduce server memory and increase performance (including the avoiding of expensive memory deallocation of hashtable arrays at the exiting of the script).
When creating arrays , if we have an element with the same value as another element from the same array, we would expect PHP instead of creating new zval container to increase the refcount and point the duplicate symbol to the same zval. This is true except for value type integer.
Example:
$arr = [‘bebe’ => ‘Bob’, ‘age’ => 23, ‘too’ => 23 ];
xdebug_debug_zval( ‘arr’ );
(refcount=2, is_ref=0)
array (size=3)
‘bebe’ => (refcount=1, is_ref=0)string ‘Bob’ (length=3)
‘age’ => (refcount=0, is_ref=0)int 23
‘too’ => (refcount=0, is_ref=0)int 23
but :
$arr = [‘bebe’ => ‘Bob’, ‘age’ => 23, ‘too’ => ’23’ ];
xdebug_debug_zval( ‘arr’ );
(refcount=2, is_ref=0)
array (size=3)
‘bebe’ => (refcount=1, is_ref=0)string ‘Bob’ (length=3)
‘age’ => (refcount=0, is_ref=0)int 23
‘too’ => (refcount=1, is_ref=0)string ’23’ (length=2)
or :
$arr = [‘bebe’ => ‘Bob’, ‘age’ => [1,2], ‘too’ => [1,2] ];
xdebug_debug_zval( ‘arr’ );
(refcount=2, is_ref=0)
array (size=3)
‘bebe’ => (refcount=1, is_ref=0)string ‘Bob’ (length=3)
‘age’ => (refcount=2, is_ref=0)
array (size=2)
0 => (refcount=0, is_ref=0)int 1
1 => (refcount=0, is_ref=0)int 2
‘too’ => (refcount=2, is_ref=0)
array (size=2)
0 => (refcount=0, is_ref=0)int 1
1 => (refcount=0, is_ref=0)int 2
This function makes (assoc.) array creation much easier:
function arr (. $array )< return $array ; >
?>
It allows for short syntax like:
$arr = arr ( x : 1 , y : 2 , z : 3 );
?>
Instead of:
$arr = [ «x» => 1 , «y» => 2 , «z» => 3 ];
// or
$arr2 = array( «x» => 1 , «y» => 2 , «z» => 3 );
?>
Sadly PHP 8.2 doesn’t support this named arguments in the «array» function/language construct.
Php array key value index
key — Fetch a key from an array
Description
key() returns the index element of the current array position.
Parameters
Return Values
The key() function simply returns the key of the array element that’s currently being pointed to by the internal pointer. It does not move the pointer in any way. If the internal pointer points beyond the end of the elements list or the array is empty, key() returns null .
Changelog
| Version | Description |
|---|---|
| 8.1.0 | Calling this function on object s is deprecated. Either convert the object to an array using get_mangled_object_vars() first, or use the methods provided by a class that implements Iterator , such as ArrayIterator , instead. |
| 7.4.0 | Instances of SPL classes are now treated like empty objects that have no properties instead of calling the Iterator method with the same name as this function. |
Examples
Example #1 key() example
$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 ), «\n» ;
>
next ( $array );
>
?>
The above example will output:
See Also
- current() — Return the current element in an array
- next() — Advance the internal pointer of an array
- array_key_first() — Gets the first key of an array
- foreach
User Contributed Notes 5 notes
Note that using key($array) in a foreach loop may have unexpected results.
When requiring the key inside a foreach loop, you should use:
foreach($array as $key => $value)
I was incorrectly using:
foreach( $array as $value )
$mykey = key ( $array );
>
?>
and experiencing errors (the pointer of the array is already moved to the next item, so instead of getting the key for $value, you will get the key to the next value in the array)
CORRECT:
foreach( $array as $key => $value )
$mykey = $key ;
>
A noob error , but felt it might help someone else out there .
Suppose if the array values are in numbers and numbers contains `0` then the loop will be terminated. To overcome this you can user like this
while ( $fruit_name = current ( $array ))
echo key ( $array ). ‘
‘ ;
next ( $array );
>
// the way will be break loop when arra(‘2’=>0) because its value is ‘0’, while(0) will terminate the loop
// correct approach
while ( ( $fruit_name = current ( $array )) !== FALSE )
echo key ( $array ). ‘
‘ ;
next ( $array );
>
//this will work properly
?>
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.
reset ( $x ); // optional.
arsort ( $x );
$key_of_max = key ( $x ); // returns the index.
?>
(Editor note: Or just use the array_keys function)
Make as simple as possible but not simpler like this one 🙂
In addition to FatBat’s response, if you’d like to find out the highest key in an array (assoc or not) but don’t want to arsort() it, take a look at this:
$arr = [ ‘3’ => 14 , ‘1’ => 15 , ‘4’ => 92 , ’15’ => 65 ];
$key_of_max = array_search ( max ( $arr ) , $arr );
- Array Functions
- array_change_key_case
- array_chunk
- array_column
- array_combine
- array_count_values
- array_diff_assoc
- array_diff_key
- array_diff_uassoc
- array_diff_ukey
- array_diff
- array_fill_keys
- array_fill
- array_filter
- array_flip
- array_intersect_assoc
- array_intersect_key
- array_intersect_uassoc
- array_intersect_ukey
- array_intersect
- array_is_list
- array_key_exists
- array_key_first
- array_key_last
- array_keys
- array_map
- array_merge_recursive
- array_merge
- array_multisort
- array_pad
- array_pop
- array_product
- array_push
- array_rand
- array_reduce
- array_replace_recursive
- array_replace
- array_reverse
- array_search
- array_shift
- array_slice
- array_splice
- array_sum
- array_udiff_assoc
- array_udiff_uassoc
- array_udiff
- array_uintersect_assoc
- array_uintersect_uassoc
- array_uintersect
- array_unique
- array_unshift
- array_values
- array_walk_recursive
- array_walk
- array
- arsort
- asort
- compact
- count
- current
- end
- extract
- in_array
- key_exists
- key
- krsort
- ksort
- list
- natcasesort
- natsort
- next
- pos
- prev
- range
- reset
- rsort
- shuffle
- sizeof
- sort
- uasort
- uksort
- usort
- each